1
HEAT AND MASS TRANSFER
LABORATORY MANUAL
UET
DEPARTMENT OF MECHANICAL
ENGINEERING (NEW CAMPUS)
UNIVERSITY OF ENGINEERING & SCIENCE TECHNOLOGY
LAHORE
ENGR. MUHAMMAD ADEEL MUNIR
(BSc. Mechanical Engineering UET, Lahore)
(MSc. Engineering Management UET, Lahore)
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Submitted by:
Name =
Registration No =
Submitted to:
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Preface
In most of the engineering institutions, the laboratory course forms an integral form of the basic
course in Heat and mass transfer at undergraduate level. The experiments to be performed in a
laboratory should ideally be designed in such a way as to reinforce the understanding of the
basic principles as well as help the students to visualize the various phenomenon
encountered in different applications.
The objective of this manual is to familiarize the students with practical skills, measurement
techniques and interpretation of results. It is intended to make this manual self-contained in all
respects, so that it can be used as a laboratory manual. In all the experiments, the relevant
theory and general guidelines for the procedure to be followed have been given. Tabular sheets
for entering the observations have also been provided in each experiment while graph sheets
have been included wherever necessary.
The students are advised to refer to the relevant text before interpreting the results and writing
a permanent discussion. The questions provided at the end of each experiment will reinforce
the students understanding of the subject and also help them to prepare for viva-voce exams.
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General Instructions To Students
• The purpose of this laboratory is to reinforce and enhance your understanding of the
fundamentals of Heat and mass transfer. The experiments here are designed to demonstrate
the applications of the basic heat transfer principles and to provide a more intuitive and
physical understanding of the theory. The main objective is to introduce a variety of
classical experimental and diagnostic techniques, and the principles behind these
techniques. This laboratory exercise also provides practice in making engineering
judgments, estimates and assessing the reliability of your measurements, skills which are
very important in all engineering disciplines.
• Read the lab manual and any background material needed before you come to the lab. You
must be prepared for your experiments before coming to the lab.
• Actively participate in class and don’t hesitate to ask questions. Utilize the teaching
assistants. You should be well prepared before coming to the laboratory, unannounced
questions may be asked at any time during the lab.
• Carelessness in personal conduct or in handling equipment may result in serious injury to
the individual or the equipment. Do not run near moving machinery. Always be on the
alert for strange sounds. Guard against entangling clothes in moving parts of machinery.
• Students must follow the proper dress code inside the laboratory. To protect clothing from
dirt, wear a lab apron. Long hair should be tied back.
• Calculator, graph sheets and drawing accessories are mandatory.
• In performing the experiments, proceed carefully to minimize any water spills, especially
on the electric circuits and wire.
• Make your workplace clean before leaving the laboratory. Maintain silence, order and
discipline inside the lab.
• Cell phones are not allowed inside the laboratory.
• Any injury no matter how small must be reported to the instructor immediately.
• Wish you a nice experience in this lab
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Table of Contents
Preface .................................................................................................................. 3
General Instructions To Students...................................................................... 4
Table of Contents ................................................................................................ 5
List of Equipment.............................................................................................. 15
List of Experiments ........................................................................................... 16
List of Figures .................................................................................................... 18
List of Tables ..................................................................................................... 19
List of Graphs .................................................................................................... 20
1. LAB SESSION 1 ......................................................................................... 21
1.1 Learning Objectives .................................................................................................. 21
1.2 Apparatus .................................................................................................................. 21
1.3 Main Parts of Linear Heat Transfer Unit .................................................................. 21
1.4 Useful Data ................................................................................................................ 21
1.5 Theory ....................................................................................................................... 22
1.5.1 Conduction Heat Transfer ............................................................................................. 22
1.5.2 Fourier’s law of heat conduction .................................................................................. 22
1.5.3 The Plane walls .............................................................................................................. 22
1.6 Experimental Procedure ............................................................................................ 22
1.7 Observations .............................................................................................................. 23
1.8 Calculated Data ......................................................................................................... 23
1.8.1 Objective:1 .................................................................................................................... 24
1.8.1.1 Specimen Calculations ............................................................................... 24
1.8.1.2 Graph: ......................................................................................................... 25
1.8.1.3 Statistical Analysis ..................................................................................... 25
1.8.1.4 Conclusion .................................................................................................. 25
1.8.2 Objective:2 .................................................................................................................... 26
1.8.2.1 Specimen Calculations ............................................................................... 26
1.8.2.2 Statistical Analysis ..................................................................................... 27
1.8.2.3 Conclusion .................................................................................................. 28
1.9 Questions ................................................................................................................... 28
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1.10 Comments .............................................................................................................. 28
2. LAB SESSION 2 ......................................................................................... 29
2.1 Learning Objective .................................................................................................... 29
2.2 Apparatus .................................................................................................................. 29
2.3 Main Parts of Linear Heat Transfer Unit .................................................................. 29
2.4 Useful Data ................................................................................................................ 29
2.5 Theory ....................................................................................................................... 30
2.5.1 Conduction Heat Transfer ............................................................................................. 30
2.5.2 Fourier’s law of heat conduction .................................................................................. 30
2.5.3 The Composite wall ....................................................................................................... 30
2.6 Experimental Procedure ............................................................................................ 31
2.7 Observations .............................................................................................................. 32
2.7.1.1 Specimen Calculations ............................................................................... 33
2.7.1.2 Graph .......................................................................................................... 34
2.7.1.3 Statistical Analysis ..................................................................................... 35
2.7.1.4 Conclusion .................................................................................................. 35
2.8 Questions ................................................................................................................... 35
2.9 Comments.................................................................................................................. 35
3. LAB SESSION NO 03 ............................................................................... 36
3.1 Learning Objective .................................................................................................... 36
3.2 Apparatus .................................................................................................................. 36
3.3 Main Parts of Radial Heat transfer unit ..................................................................... 36
3.4 Useful Data ................................................................................................................ 36
3.4.1 Radial Heat Conduction ................................................................................................ 36
3.4.2 Heated disc:................................................................................................................... 36
3.5 Theory ....................................................................................................................... 36
3.5.1 Conduction Heat Transfer ............................................................................................. 36
3.5.2 Radial Systems .............................................................................................................. 36
3.5.2.1 Cylinders ..................................................................................................... 36
3.6 Procedure ................................................................................................................... 37
3.7 Observations .............................................................................................................. 38
3.8 Calculated Data ......................................................................................................... 38
3.8.1 Objective ....................................................................................................................... 38
3.8.1.1 Specimen Calculations ............................................................................... 39
3.8.1.2 Conclusion .................................................................................................. 39
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3.8.1.3 Graph .......................................................................................................... 40
3.9 Statistical Analysis .................................................................................................... 40
3.10 Questions ............................................................................................................... 40
3.11 Comments .............................................................................................................. 40
4. LAB SESSION 4 ......................................................................................... 41
4.1 Learning Objectives .................................................................................................. 41
4.2 Apparatus .................................................................................................................. 41
4.3 Main Parts ................................................................................................................. 41
4.4 Useful Data ................................................................................................................ 41
4.5 Theory ....................................................................................................................... 41
4.5.1 Radiation ....................................................................................................................... 41
4.5.2 Radiation Heat Transfer ................................................................................................ 41
4.5.3 Inverse square law ........................................................................................................ 42
4.5.4 Stefan–Boltzmann law .................................................................................................. 42
4.6 Procedure ................................................................................................................... 42
4.7 Observations: ............................................................................................................. 44
4.8 Calculated Data ......................................................................................................... 44
4.8.1 Objective:01 .................................................................................................................. 44
4.8.1.1 Graph .......................................................................................................... 45
4.8.1.2 Conclusion .................................................................................................. 45
4.8.2 Objective:02 .................................................................................................................. 45
4.8.2.1 Specimen Calculation ................................................................................. 45
4.8.2.2 Conclusion .................................................................................................. 46
4.9 Statistical Analysis .................................................................................................... 46
4.10 Questions ............................................................................................................... 46
4.11 Comments .............................................................................................................. 46
5. LAB SESSION 5 ......................................................................................... 47
5.1 Apparatus .................................................................................................................. 47
5.2 Main Parts ................................................................................................................. 47
5.3 Useful Data ................................................................................................................ 47
5.4 Theory ....................................................................................................................... 47
5.4.1 Radiation ....................................................................................................................... 47
5.4.2 Shape Factor ................................................................................................................. 47
5.5 Procedure ................................................................................................................... 48
5.6 Observations: ............................................................................................................. 49
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5.6.1 Calculated Data ............................................................................................................. 50
5.6.1.1 Specimen Calculation ................................................................................. 50
5.6.1.2 Conclusion .................................................................................................. 51
5.7 Statistical Analysis .................................................................................................... 51
5.8 Questions ................................................................................................................... 51
5.9 Comments.................................................................................................................. 51
6. LAB SESSION 6 ......................................................................................... 52
6.1 Learning Objective .................................................................................................... 52
6.2 Apparatus .................................................................................................................. 52
6.3 Main Parts ................................................................................................................. 52
6.4 Useful Data ................................................................................................................ 52
6.5 Theory ....................................................................................................................... 53
6.6 Procedure ................................................................................................................... 53
6.7 Calculated Data ......................................................................................................... 55
6.7.1 Objective:01 .................................................................................................................. 55
6.7.1.1 Observations ............................................................................................... 55
6.7.1.2 Specimen Calculations ............................................................................... 55
6.7.1.3 Graph .......................................................................................................... 56
6.7.1.4 Conclusion .................................................................................................. 56
6.8 Statistical Analysis .................................................................................................... 57
6.9 Questions ................................................................................................................... 57
6.10 Comments .............................................................................................................. 57
7. LAB SESSION 7 ......................................................................................... 58
7.1 Learning Objective .................................................................................................... 58
7.2 Apparatus .................................................................................................................. 58
7.3 Main Parts ................................................................................................................. 58
7.4 Useful Data ................................................................................................................ 58
7.5 Theory ....................................................................................................................... 59
7.5.1 Forced convection ......................................................................................................... 59
7.6 Procedure ................................................................................................................... 59
7.6.1 Objective ....................................................................................................................... 61
7.6.1.1 Observations ............................................................................................... 61
7.6.1.2 Calculated Data ........................................................................................... 61
7.6.1.3 Specimen Calculations ............................................................................... 61
7.6.1.4 Graph: ......................................................................................................... 63
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7.6.1.5 Conclusion .................................................................................................. 63
7.7 Statistical Analysis .................................................................................................... 63
7.8 Questions ................................................................................................................... 63
7.9 Comments.................................................................................................................. 63
8. LAB SESSION 8 ......................................................................................... 67
8.1 Learning Objective .................................................................................................... 67
8.2 Apparatus .................................................................................................................. 67
8.3 Main Parts ................................................................................................................. 67
8.4 Useful Data ................................................................................................................ 67
8.5 Theory: ...................................................................................................................... 67
8.5.1 Fin (extended surface) .................................................................................................. 67
8.6 Procedure:.................................................................................................................. 68
8.7 Observations .............................................................................................................. 69
8.8 Calculated Data ......................................................................................................... 70
8.8.1 Specimen Calculation .................................................................................................... 70
8.8.2 Graph............................................................................................................................. 71
8.8.3 Conclusion ..................................................................................................................... 71
8.9 Questions ................................................................................................................... 71
8.10 Comments .............................................................................................................. 71
9. LAB SESSION 9 ......................................................................................... 72
9.1 Learning Objective .................................................................................................... 72
9.2 Apparatus .................................................................................................................. 72
9.3 Main Parts ................................................................................................................. 72
9.4 Theory ....................................................................................................................... 72
9.5 Procedure:.................................................................................................................. 73
9.6 Observations .............................................................................................................. 73
9.6.1 Objective ....................................................................................................................... 74
9.6.1.1 Graph .......................................................................................................... 75
9.6.1.2 Conclusion .................................................................................................. 75
9.7 Comments.................................................................................................................. 75
10. LAB SESSION 10 ................................................................................... 76
10.1 Learning Objective ................................................................................................ 76
10.2 Apparatus ............................................................................................................... 76
10.3 Main Parts .............................................................................................................. 76
10.4 Theory .................................................................................................................... 76
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10.4.1 Transient Heat-Transfer ................................................................................................ 76
10.4.2 Lumped-Heat-Capacity System ..................................................................................... 76
10.4.3 Biot number (Bi) ............................................................................................................ 76
10.4.4 Fourier number (Fo) ...................................................................................................... 77
10.4.5 Heisler charts ................................................................................................................ 78
10.5 Procedure ............................................................................................................... 78
10.6 Observations .......................................................................................................... 80
10.7 Calculated Data ...................................................................................................... 81
10.7.1 Sample Calculations ...................................................................................................... 81
10.7.2 Graph............................................................................................................................. 83
10.7.3 Conclusion ..................................................................................................................... 83
10.8 Statistical Analysis ................................................................................................ 83
10.9 Questions ............................................................................................................... 83
10.10 Comments .............................................................................................................. 83
11. LAB SESSION 11 ................................................................................... 85
11.1 Learning Objective ................................................................................................ 85
11.2 Apparatus ............................................................................................................... 85
11.3 Main Parts .............................................................................................................. 85
11.4 Useful Data ............................................................................................................ 85
11.5 Theory .................................................................................................................... 86
11.5.1 Introduction of The Equipment .................................................................................... 86
11.5.2 Description of The Equipment ...................................................................................... 87
11.6 Objective: 1............................................................................................................ 87
11.6.1 Procedure ...................................................................................................................... 87
11.6.2 Observations ................................................................................................................. 88
11.6.3 Graph............................................................................................................................. 88
11.6.4 Conclusion ..................................................................................................................... 88
11.7 Objective: 2............................................................................................................ 88
11.7.1 Procedure ...................................................................................................................... 89
11.7.2 Observations: ................................................................................................................ 89
11.7.3 Graph............................................................................................................................. 89
11.7.4 Conclusion ..................................................................................................................... 89
11.8 Specimen Calculation ............................................................................................ 89
11.9 Statistical Analysis ................................................................................................ 89
11.10 Questions ............................................................................................................... 90
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11.11 Comments .............................................................................................................. 90
12. LAB SESSION 12 ................................................................................... 91
12.1 Learning Objective ................................................................................................ 91
12.2 Apparatus ............................................................................................................... 91
12.3 Main Parts .............................................................................................................. 91
12.4 Useful Data ............................................................................................................ 92
12.4.1 Interior Tube ................................................................................................................. 92
12.4.2 Exterior Tube ................................................................................................................. 92
12.4.3 Base Unit ....................................................................................................................... 92
12.4.4 Heat Exchanger ............................................................................................................. 92
12.4.5 Physical Properties of The Hot And Cold Water ........................................................... 92
12.4.6 Mass Flow Rates ............................................................................................................ 92
12.5 Theory .................................................................................................................... 93
12.5.1 Heat transference in heat exchangers .......................................................................... 93
12.5.2 Overall Heat-Transfer Coefficient ................................................................................. 94
12.5.3 The Log Mean Temperature Difference (LMTD) ........................................................... 94
12.5.4 Effectiveness-Ntu Method ............................................................................................ 94
12.5.5 Capacity coefficient ....................................................................................................... 94
12.5.6 Reynolds number .......................................................................................................... 95
12.6 Objective 01 ........................................................................................................... 95
12.6.1 Procedure: ..................................................................................................................... 95
12.6.2 Observations ................................................................................................................. 96
12.6.3 Calculated Data ............................................................................................................. 96
12.6.4 Specimen Calculations .................................................................................................. 97
12.6.4.1 Heat transferred by the hot water ............................................................... 97
12.6.4.2 Heat absorbed by the cold water ................................................................. 97
12.6.4.3 Heat Losses ................................................................................................. 97
12.6.4.4 Logarithmic temperatures mean difference between hot water and cold
water 97
12.6.4.5 Global heat transference coefficient= (U) .................................................. 97
12.7 Objective:02........................................................................................................... 97
12.7.1 Procedure ...................................................................................................................... 97
12.7.2 Observations ................................................................................................................. 98
12.7.3 Calculations ................................................................................................................... 99
12.7.4 Specimen Calculations .................................................................................................. 99
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12.7.4.1 Heat transferred by the hot water ............................................................... 99
12.7.4.2 Logarithmic temperatures mean difference between hot water and cold
water 99
12.7.4.3 Number of transmission units ................................................................... 100
12.7.4.4 Capacity coefficient .................................................................................. 100
12.8 Graph ................................................................................................................... 100
12.9 Statistical Analysis .............................................................................................. 100
12.10 Conclusion ........................................................................................................... 100
12.11 Questions ............................................................................................................. 101
12.12 Comments ............................................................................................................ 101
13. LAB SESSION 13 ................................................................................. 102
13.1 Learning Objective .............................................................................................. 102
13.2 Apparatus ............................................................................................................. 102
13.3 Main Parts ............................................................................................................ 102
13.4 Useful Data .......................................................................................................... 103
13.4.1 Interior Tube ............................................................................................................... 103
13.4.2 Exterior Tube ............................................................................................................... 103
13.4.3 Base Unit ..................................................................................................................... 103
13.4.4 Heat Exchanger ........................................................................................................... 103
13.4.5 Physical Properties Of The Hot And Cold Water ......................................................... 103
13.4.6 Mass Flow Rates .......................................................................................................... 104
13.5 Theory .................................................................................................................. 105
13.5.1 Heat transference in heat exchangers ........................................................................ 105
13.5.2 Shell and tube heat exchanger.................................................................................... 105
13.5.3 Overall Heat-Transfer Coefficient ............................................................................... 105
13.5.4 The Log Mean Temperature Difference (LMTD) ......................................................... 106
13.5.5 Effectiveness-Ntu Method .......................................................................................... 106
13.5.6 Capacity coefficient ..................................................................................................... 106
13.5.7 Reynolds number ........................................................................................................ 106
13.6 Objective 1 ........................................................................................................... 107
13.6.1 Procedure: ................................................................................................................... 107
13.6.2 Observations ............................................................................................................... 107
13.6.3 Calculated Data ........................................................................................................... 108
13.6.4 Specimen Calculations ................................................................................................ 108
13.6.4.1 Heat transferred by hot water (q
h
) ............................................................ 108
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13.6.4.2 Heat absorbed by the cold water (q
c
) ........................................................ 108
13.6.4.3 Heat losses (q
l
) .......................................................................................... 108
13.6.4.4 Logarithmic average temperatures difference between hot and cold water
(∆T
lm
) 108
13.6.4.5 Global heat transfer coefficient (U) .......................................................... 108
13.7 Objective 2 ........................................................................................................... 109
13.7.1 Procedure .................................................................................................................... 109
13.7.2 Observations ............................................................................................................... 109
13.7.3 Calculated Data ........................................................................................................... 110
13.7.4 Specimen Calculations ................................................................................................ 110
13.7.4.1 Experimental effectiveness (ϵ) ................................................................. 110
13.7.4.2 Logarithmic average temperatures difference between hot and cold water
(∆T
lm
) 110
13.7.4.3 Global heat transfer coefficient (U) .......................................................... 110
13.7.4.4 Number of transmission units ................................................................... 110
13.7.4.5 Capacity coefficient .................................................................................. 111
13.7.4.6 Temperatures at the exchanger outlet ....................................................... 111
13.8 Statistical Analysis .............................................................................................. 111
13.9 Conclusion ........................................................................................................... 111
13.10 Questions ............................................................................................................. 111
13.11 Comments ............................................................................................................ 111
14. LAB SESSION 14 ................................................................................. 112
14.1 Learning Objective .............................................................................................. 112
14.2 Apparatus ............................................................................................................. 112
14.3 Main Parts ............................................................................................................ 112
14.4 Useful Data .......................................................................................................... 112
14.4.1 BASE UNIT ................................................................................................................... 112
14.4.2 Heat Exchanger ........................................................................................................... 112
14.4.3 Physical Properties of The Hot and Cold Water .......................................................... 113
14.4.4 Mass Flow Rates .......................................................................................................... 113
14.5 Theory .................................................................................................................. 115
14.5.1 Heat transference in heat exchangers ........................................................................ 115
14.5.2 Plate heat exchanger .................................................................................................. 115
14.5.3 Overall Heat-Transfer Coefficient ............................................................................... 115
14.5.4 The Log Mean Temperature Difference (LMTD) ......................................................... 115
14.6 Objective .............................................................................................................. 116
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14.6.1 Procedure .................................................................................................................... 116
14.6.2 Observations ............................................................................................................... 116
14.6.3 Calculated Data ........................................................................................................... 117
14.6.4 Specimen Calculations ................................................................................................ 117
14.6.4.1 Heat transferred by hot water (q
h
) ............................................................ 117
14.6.4.2 Heat absorbed by the cold water (q
c
) ........................................................ 117
14.6.4.3 Heat losses (q
l
) .......................................................................................... 117
14.6.4.4 Logarithmic average temperatures difference between hot and cold water
(∆T
lm
) 117
14.6.4.5 Global heat transfer coefficient (U) .......................................................... 117
14.7 Graph ................................................................................................................... 118
14.8 Statistical Analysis .............................................................................................. 118
14.9 Conclusion ........................................................................................................... 118
14.10 Questions ............................................................................................................. 118
14.11 Comments ............................................................................................................ 118
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List of Equipment
1) Linear Heat Transfer Unit (H111A)
2) Radial Heat Transfer Unit (H111B)
3) Radiation Heat Transfer Unit (H111C)
4) Combined Convection & Radiation Heat Transfer Unit (H111D)
5) Extended Surface Heat Transfer Unit (H111E)
6) Radiation Errors in Temperature Measurements (H111F)
7) Heat Transfer Service Unit with Unsteady State Heat Transfer Unit (H111G)
8) Free and Forced Convection Heat Transfer Unit (TCLFC)
9) Turbulent Flow Heat Exchanger (TIFT)
10) Shell and Tube Heat Exchanger (TICT)
11) Plate Heat Exchanger (TIPL)
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List of Experiments
Experiment No.
Description
Experiment No. 1
To apply Fourier Rate Equation for steady flow of heat through plane solid
materials.
Experiment No. 2
To apply Fourier Rate Equation for steady flow of heat through composite
plate
Experiment No. 3
To apply the Fourier Rate Equation for steady flow of heat through cylindrical
solid materials
Experiment No. 4
To verify laws of radiation by using shape factor
Experiment No. 5
To verify the role of shape factor involved in radiation heat transfer
Experiment No. 6
To calculate the total heat transfer of combined convection and radiation
heat transfer mechanism
Experiment No. 7
To calculate the total heat transfer of combined “forced convection” and
“radiation” heat transfer mechanism
Experiment No. 8
To experimentally verify the heat transfer from an extended surface from
combined modes of free conduction, free convection and radiation heat
transfer by comparing it with the theoretical analysis
Experiment No. 9
To Reduce radiation errors in measurement of temperature by using shield
between sensor and source of radiation
Experiment No. 10
To determine the Convective heat transfer coefficient of a solid cylinder
using analytical transient temperature/heat flow charts
Experiment No. 11
To measure the effect of different exchanger geometry on convection heat
transfer mechanism
Experiment No. 12
To Calculate logarithmic mean temperature difference (LMTD), global heat
transfer coefficient and effectiveness of turbulent flow heat exchanger
Experiment No. 13
To Calculate logarithmic mean temperature difference (LMTD), global heat
transfer coefficient and effectiveness of shell and tube heat exchanger
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Experiment No. 14
To Calculate logarithmic mean temperature difference (LMTD) and global
heat transfer coefficient of plate heat exchanger
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List of Figures
Figure 1.1: Temperature Profile in Fourier heat conduction ................................................... 22
Figure.1.2: Schematic diagram of experiment ........................................................................ 24
Figure.1.3: Schematic diagram of experiment ........................................................................ 25
Figure 1.4: Schematic diagram of experiment ........................................................................ 26
Figure 2.1: Temperature Profile in Fourier heat conduction ................................................... 30
Figure 2.2: Heat through composite wall ................................................................................. 31
Figure 2.3: Schematic diagram of experiment ........................................................................ 32
Figure 2.4: Schematic diagram of experiment ......................................................................... 34
Figure 3.1: Heat transfer through cylinder ............................................................................... 37
Figure 3.2: Temperature distribution in cylinder ..................................................................... 37
Figure 4.1: Schematic diagram of experiment ........................................................................ 43
Figure.5.1: Schematic diagram for shape factor ..................................................................... 47
Figure 5.2: Schematic diagram of experiment ........................................................................ 48
Figure 6.1: Schematic Diagram of Experiment ...................................................................... 54
Figure 7.1: Schematic Diagram of Experiment ...................................................................... 60
Figure 8.1: Schematic Diagram of Experiment ...................................................................... 69
Figure 8.1: Schematic Diagram of Experiment ...................................................................... 86
Figure 12.1: Schematic Diagram of Experiment ..................................................................... 93
Figure 13.1: Schematic Diagram of Experiment ................................................................... 104
Figure 13.2: Parallel and counter parallel flow ...................................................................... 105
Figure 13.3: Shell and tube heat exchanger ........................................................................... 105
Figure 14.1: Schematic Diagram of Experiment ................................................................... 114
Figure 14.2: Parallel and counter parallel flow ...................................................................... 115
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List of Tables
Table 1.1: Temperatures observation at different points of specimen ..................................... 23
Table 1.2: Calculation of thermal conductivity ....................................................................... 24
Table 1.3: Distribution of temperature through uniform plane wall ........................................ 26
Table 2.1: Temperatures observation at different points of specimen ..................................... 32
Table 2.2: Calculation of overall heat transfer coefficient ...................................................... 33
Table 3.1: Distribution of temperature for different voltages .................................................. 38
Table 3.2: Thermal conductivity of given sample ................................................................... 39
Table 4.1: Measurement of temperatures from radiometer ..................................................... 44
Table 4.2: Calculation of intensity of radian ........................................................................... 45
Table 4.3: Calculation of shape factor ..................................................................................... 45
Table 5.1: Measurement of temperatures from radiometer ..................................................... 49
Table 5.2: Radiation incident on the detector .......................................................................... 50
Table 6.1: Table of Physical properties of Air at Atmospheric Pressure ................................. 52
Table 6.2: Measurement of temperature for free convection ................................................... 55
Table 6.3: Heat transfer due to free convection and radiation ................................................. 55
Table 7.1: Table of Physical properties of Air at Atmospheric Pressure ................................. 58
Table 7.2: Measurement of temperature due to forced convection ......................................... 61
Table 7.3: Heat transfer due to forced convection ................................................................... 61
Table 8.1: Temperatures measured at different distances from T1 ......................................... 69
Table 8.2: Heat transfer from extended surface ....................................................................... 70
Table 9.1: Temperatures at different points from radiant source ............................................. 74
Table 10.1: Specimen: 20mm diameter Brass Cylinder. ......................................................... 80
Table 10.2: Specimen: 20mm Stainless Steel Cylinder ........................................................... 80
Table 10.3: Properties of Specimen: 20mm diameter Brass Cylinder .................................... 81
Table 10.4: Properties of Specimen: 20mm diameter stainless steel Cylinder ....................... 81
Table 11.1: Temperatures in free convection .......................................................................... 88
Table 11.2: Temperatures in forced convection ...................................................................... 88
Table 11.3: Temperatures for different geometry of exchangers ............................................ 89
Table 12.1: Temperature at different points of turbulent flow heat exchanger ....................... 96
Table 12.2: Heat transfer calculation in turbulent flow heat exchanger .................................. 96
Table 12.3: Temperature for parallel and cross flow ............................................................... 98
Table 12.4: Effectiveness of turbulent flow exchanger ........................................................... 99
Table 13.1: Valve positions of shell and tube heat exchanger ............................................... 104
Table 13.2: Temperatures at shell and tube heat exchanger .................................................. 107
Table13.3: Heat transfer coefficient of shell and tube heat exchanger .................................. 108
Table 13.4: Temperatures for shell and tube heat exchanger ................................................ 109
Table 13.5: Effectiveness of shell and tube heat exchanger .................................................. 110
Table 14.1: Position of valves in plate heat exchanger .......................................................... 114
Table 14.2: Temperatures of Plate Heat Exchangers ............................................................. 116
Table14.3: Heat transfer in Plate heat exchanger .................................................................. 117
20
List of Graphs
Graph 7.1: Kinematic velocity of air at standard Pressure ...................................................... 64
Graph 7.2: Thermal conductivity of air at standard pressure ................................................... 65
Graph 7.3: Prandtl number of air at standard pressure ........................................................... 66
Graph 10.1: Heisler charts ....................................................... Error! Bookmark not defined.
21
1. LAB SESSION 1
To apply Fourier Rate Equation for steady flow of heat through plane solid materials.
1.1 Learning Objectives
[i] To identify a given sample by determining its thermal conductivity.
[ii] To measure temperature distribution through a uniform plane wall and analyse the
effect of a change in heat flow.
1.2 Apparatus
Linear Heat Transfer unit H111A (Serial no H111A/04417)
1.3 Main Parts of Linear Heat Transfer Unit
1) Hydraulic Bench
2) Specimen of different materials (Brass, Aluminium, Stainless Steel)
3) Main digital Control panel (H111)
4) Temperature Sensors
1.4 Useful Data
Heated Section:
Material: Brass 25 mm diameters, Thermocouples T1, T2, T3 at 15mm spacing. Thermal
Conductivity: Approximately 121 W/mK
Cooled Section:
Material: Brass 25 mm diameters, Thermocouples T6, T7, T8 at 15mm spacing. Thermal
Conductivity: Approximately 121 W/mK
Brass Intermediate Specimen:
Material: Brass 25 mm diameters * 30mm long. Thermocouples T4, T5 at 15mm spacing
centrally spaced along the length. Thermal Conductivity: Approximately 121 W/mK
Hot and Cold Face Temperature:
Due to the need to keep the spacing of the thermocouples constant at 15mm with, or
without the intermediate specimens in position the thermocouples are displaced 7.5 mm
back from the ends faces of the heated and cooled specimens and similarly located for the
Brass Intermediate Specimen.
T
hot face
= T
3
-
T
cold face
=
+
So that the equations are of the above form as the distance between T3 and the hot face
and T6 and the cold face are equal to half the distance between the adjacent pairs of
thermocouples.
22
1.5 Theory
1.5.1 Conduction Heat Transfer
When a temperature gradient exists in a body, there is an energy transfer from the high-
temperature region to the low-temperature region. The energy is transferred by conduction
and that the heat-transfer rate per unit area is proportional to the normal temperature gradient
1.5.2 Fourier’s law of heat conduction
Figure 1.1: Temperature Profile in Fourier heat conduction
q
x
=-KA
Equation I.1: Fourier law heat conduction equation
Where q
x
is the heat-transfer rate and ∂T/∂x is the temperature gradient in the direction of the
heat flow. The positive constant k is called the thermal conductivity of the material, and the
minus sign is inserted so that the second principle of thermodynamics will be satisfied; i.e.,
heat must flow downhill on the temperature scale as shown in figure 1.1. Equation 1.1 is called
Fourier’s law of heat conduction after the French mathematical physicist Joseph Fourier, who
made very significant contributions to the analytical treatment of conduction heat transfer.
(Equation 1.1) is the defining equation for the thermal conductivity and that k has the units of
watts per meter per Cels1ius degree in a typical system of units in which the heat flow is
expressed in watts
1.5.3 The Plane walls
First consider the plane wall where a direct application of Fourier’s law. Integration yields
q=-
(T
2
-T
1
) Equation 1.2: Integration of Fourier law
When the thermal conductivity is considered constant. The wall thickness is x, and T
1
and T
2
are the wall-face temperatures.
1.6 Experimental Procedure
1. Ensure that the main switch is in the off position (the digital displays should not be
illuminated). Ensure that the residual current circuit breaker on the rear panel is in the
ON position.
2. Turn the voltage controller anti-clockwise to set the AC voltage to minimum.
23
3. Ensure the cold-water supply and electrical supply is turned on at the source. Open the
water tap until the flow through the drain hose is approximately 1.5 litters/minute.
4. Release the toggle clamp tensioning screw and clamps. Ensure that the faces of the
exposed ends of the heated and cooled sections are clean.
5. Turn on the main switch and the digital displays should illuminate. Set the temperature
selector switch to T1 to indicate the temperature of the heated end of the bar.
6. Following the above procedure ensure cooling water is flowing and then set the heater
voltage V to approximately 150 volts. This will provide a reasonable temperature
gradient along the length of the bar. If however the local cooling water supply is at a
high temperature (25-35 or more) then it may be necessary to increase the voltage
supplied to the heater. This will increase the temperature difference between the hot
and cold ends of the bar.
7. Monitor temperatures T1, T2, T3, T4, T5, T6, T7, T8 until stable. When the
temperatures are stabilized record T1, T2, T3, T4, T5, T6, T7, T8, V, I
8. Increase the heater voltage by approximately 50 volts and repeat the above procedure
again recording the parameters T1, T2, T3, T4, T5, T6, T7, T8, V, I when temperature
have stabilized.
9. When the experimental procedure is completed, it is good practice to turn off the power
to the heater by reducing the voltage to zero and allow the system a short time to cool
before turning off the cooling water supply.
1.7 Observations
Sample
No.
T
1
T
2
T
3
T
4
T
5
T
6
T
7
T
8
V
I
Volts
Amps
1
2
3
4
Distance
from T1
0.000
0.015
0.030
0.045
0.060
0.075
0.090
0.105
Table 1.1: Temperatures observation at different points of specimen
1.8 Calculated Data
24
1.8.1 Objective:1
To identify a given sample by determining its thermal conductivity.
Figure.1.2: Schematic
diagram of experiment
Specimen cross sectional Area A=0.00049m
2
Specimen Length =0.030m
Sample
No.
Material
Name
1
2
3
4
Table 1.2: Calculation of thermal conductivity
1.8.1.1 Specimen Calculations
Intermediate Specimen and hot and cold section cross sectional Area;
Heat transfer rate from the heater;
Note that the thermocouples T3 and T6 do not record the hot face and cold face temperatures,
as are both displaced by 0.0075m from T3 and T6 as shown.
25
Figure.1.3: Schematic diagram of
experiment
If it is assumed that the temperature distribution is linear, then the actual temperature at the hot
face and cold face may be determined from the following equations.
T
hot face
= T
3
-
And
T
cold face
=
+
From the above parameters, the thermal conductivity of the aluminum intermediate section
may be calculated.
1.8.1.2 Graph:
Plot a graph b/w Temperature and Distance from T1 thermocouple. The thermal conductivity
of the intermediate sample may also be calculated from the data it is plotted on a graph. From
the graph the slope of the line is.
X
1.8.1.3 Statistical Analysis
For Thermal conductivity
% Error=
x
avg
=
S
x
=
1.8.1.4 Conclusion
26
1.8.2 Objective:2
To measure the temperature distribution through a uniform plane wall and demonstrate the effect of a
change in heat flow.
Figure 1.4: Schematic diagram of
experiment
Sample
No.
1-3
6-8
1-3
6-8
W
m
M
/m
/m
W/mK
W/mK
1
2
3
4
Table 1.3: Distribution of temperature through uniform plane wall
1.8.2.1 Specimen Calculations
Heat transfer rate from the heater;
Temperature difference in the heated section between T1 and T3;
Similarly the temperature difference in the cooled section between T6 and T8;
27
The distance between the temperatures measuring points, T1 and T3and T6 and T8, are
similar;
=
=
Hence the temperature gradient along the heated and cooled sections may be calculated from
If the constant rate of heat transfer is divided by the temperature gradients, the value obtained
will be similar if the equation is valid.
Hence, substituting the values obtained gives for the heated section and cooled sections
respectively for following values.
As may be seen from the above example and the tabulated data the function does result in a
constant value within the limits of the experimental data.
1.8.2.2 Statistical Analysis
For Constant “C”
% Error=
x
avg
=
S
x
=
28
1.8.2.3 Conclusion
1.9 Questions
1) What is conduction heat transfer?
2) What is Fourier law of heat conduction
3) What is meant by thermal resistance
1.10 Comments
29
2. LAB SESSION 2
To apply Fourier Rate Equation for steady flow of heat through composite plate
2.1 Learning Objective
I. To measure the temperature distribution through a composite plane wall and determine the
overall Heat Transfer Coefficient for the flow of heat through a combination of different
materials
2.2 Apparatus
Linear Heat Transfer unit H111A (Serial no H111A/04417)
2.3 Main Parts of Linear Heat Transfer Unit
5) Hydraulic Bench
6) Specimen of different materials (Brass, Aluminium, Stainless Steel)
7) Main digital Control panel (H111)
8) Temperature Sensors
2.4 Useful Data
Heated Section:
Material: Brass 25 mm diameters, Thermocouples T1, T2, T3 at 15mm spacing. Thermal
Conductivity: Approximately 121 W/mK
Cooled Section:
Material: Brass 25 mm diameters, Thermocouples T6, T7, T8 at 15mm spacing. Thermal
Conductivity: Approximately 121 W/mK
Brass Intermediate Specimen:
Material: Brass 25 mm diameters * 30mm long. Thermocouples T4, T5 at 15mm spacing
centrally spaced along the length. Thermal Conductivity: Approximately 121 W/mK
Stainless Steel Intermediate Specimen:
Material: Stainless Steel, 25 mm diameters * 30mm long. No Thermocouples fitted.
Thermal Conductivity: Approximately 25 W/mK
Aluminum Intermediate Specimen:
Material: Aluminum Alloy, 25 mm diameters * 30mm long. No Thermocouples fitted.
Thermal Conductivity: Approximately 180 W/mK
Hot and Cold Face Temperature:
Due to the need to keep the spacing of the thermocouples constant at 15mm with, or
without the intermediate specimens in position the thermocouples are displaced 7.5 mm
30
back from the ends faces of the heated and cooled specimens and similarly located for the
Brass Intermediate Specimen.
T
hot face
= T
3
-
T
cold face
=
+
So that the equations are of the above form as the distance between T3 and the hot face
and T6 and the cold face are equal to half the distance between the adjacent pairs of
thermocouples.
2.5 Theory
2.5.1 Conduction Heat Transfer
When a temperature gradient exists in a body, there is an energy transfer from the high-
temperature region to the low-temperature region. The energy is transferred by conduction
and that the heat-transfer rate per unit area is proportional to the normal temperature gradient
2.5.2 Fourier’s law of heat conduction
Figure 2.1: Temperature Profile in Fourier heat conduction
q
x
=-KA
Equation 2.1: Fourier law heat conduction equation
Where q
x
is the heat-transfer rate and ∂T/∂x is the temperature gradient in the direction of the
heat flow. The positive constant k is called the thermal conductivity of the material, and the
minus sign is inserted so that the second principle of thermodynamics will be satisfied; i.e.,
heat must flow downhill on the temperature scale as shown in figure 1.1. Equation 1.1 is called
Fourier’s law of heat conduction after the French mathematical physicist Joseph Fourier, who
made very significant contributions to the analytical treatment of conduction heat transfer.
(Equation 1.1) is the defining equation for the thermal conductivity and that k has the units of
watts per meter per Cels1ius degree in a typical system of units in which the heat flow is
expressed in watts
2.5.3 The Composite wall
If more than one material is present, as in the multilayer wall shown in Figure 2, the analysis
would proceed as follows: The temperature gradients in the three materials are shown, and
the heat flow may be written
31
q=−k
A
A
= −k
B
A
= −k
C
A
Equation 2.2: Heat through composite wall
Note that the heat flow must be the same through all sections
Figure 2.2: Heat through composite wall
Solving these three equations simultaneously, the heat flow is written
q=
Equation 2.3: Heat flow equation through composite wall
With composite systems, it is often convenient to work with an overall heat transfer
coefficient U, which is defined by an expression analogous to Newton’s law of cooling.
Accordingly
Q=UA∆T Equation 2.4: Overall heat transfer coefficient
Where ∆T is the overall temperature difference. Readers can read Further detail from book
“heat transfer by J.P Holman” in “chapter 2”
2.6 Experimental Procedure
1. Ensure that the main switch is in the off position (the digital displays should not be
illuminated). Turn the voltage controller anti-clockwise to set the AC voltage to
minimum.
2. Ensure the cold-water supply and electrical supply is turned on at the source. Open the
water tap until the flow through the drain hose is approximately 1.5 litters/minute.
3. Release the toggle clamp tensioning screw and clamps. Ensure that the faces of the
exposed ends of the heated and cooled sections are clean. Similarly, check the faces of
the Intermediate specimen to be placed between the faces of the heated and cooled
section.
4. Turn on the main switch and the digital displays should illuminate. Set the temperature
selector switch to T1 to indicate the temperature of the heated end of the bar.
5. Following the above procedure ensure cooling water is flowing and then set the heater
voltage V to approximately 150 volts. This will provide a reasonable temperature
gradient along the length of the bar. If, however the local cooling water supply is at a
32
high temperature (25-35 or more) then it may be necessary to increase the voltage
supplied to the heater. This will increase the temperature difference between the hot
and cold ends of the bar.
6. Monitor temperatures T1, T2, T3, T4, T5, T6, T7, T8 until stable.
7. Increase the heater voltage by approximately 50 volts and repeat the above procedure
again recording the parameters T1, T2, T3, T4, T5, T6, T7, T8, V, I when temperature
have stabilized.
2.7 Observations
Sample
No.
T
1
T
2
T
3
T
4
T
5
T
6
T
7
T
8
V
I
Volts
Amps
1
2
3
4
Distance
from T1
0.000
0.015
0.030
0.045
0.060
0.075
0.090
0.105
Table 2.1: Temperatures observation at different points of specimen
To measure the temperature distribution through a composite plane wall and determine the overall Heat
Transfer Coefficient for the flow of heat through a combination of different materials in use.
Figure 2.3: Schematic diagram of experiment
33
Specimen cross sectional Area A = 0.00049m
2
Conductivity of Brass heated and cooled section =121
Conductivity of Stainless steel intermediate section =25
Sample
No.
Q
--
W
K
m
M
m
1
2
3
4
Table 2.2: Calculation of overall heat transfer coefficient
2.7.1.1 Specimen Calculations
Brass Intermediate Specimen and hot and cold section cross sectional Area;
The temperature difference across the bar from T1 to T8;
X
Note that
and
are the distances between the thermocouple T1 and the hot face and
the cold face and the thermocouple T8 respectively. Similarly
is the distance between the
hot face and cold face of the intermediate stainless steel section.
Sample No.
--
1
2
3
4
34
Figure 2.4: Schematic diagram of experiment
The distances between surfaces are therefore as follows.
0.0375m
0.030m
0.0375m
Heat transfer rate from the heater;
Hence
Similarly,
Note that the U value resulting from the test data differs from that resulting from assumed
thermal conductivity and material thickness. This is most likely due to un-accounted for heat
losses and thermal resistances between the hot face interface and cold face inter face with the
stainless steel intermediate section.
2.7.1.2 Graph
Plot a graph b/w Temperature and Distance from T
1
thermocouple. The temperature data may
be plotted against position along the bar and straight lines drawn through the temperature points
for the heated and cooled sections. Then a straight line may be drawn through the hot face and
35
cold face temperature to extrapolate the temperature distribution in the stainless steel
intermediate section.
2.7.1.3 Statistical Analysis
For Constant “U”
% Error=
x
avg
=
S
x
=
2.7.1.4 Conclusion
2.8 Questions
1) Define Overall heat transfer coefficient
2) Define thermal conductivity and explain its significance in heat transfer.
2.9 Comments
36
3. LAB SESSION NO 03
To apply the Fourier Rate Equation for steady flow of heat through cylindrical solid materials
3.1 Learning Objective
[i] To identify a given sample (disc material) by determining its thermal conductivity.
3.2 Apparatus
Radial Heat Transfer unit H111B
3.3 Main Parts of Radial Heat transfer unit
1) Hydraulic Bench
2) Specimen of different materials
3) Main digital Control panel (H111)
4) Temperature Sensors
3.4 Useful Data
3.4.1 Radial Heat Conduction
3.4.2 Heated disc:
Material: Outside Diameter: 0.110m
Diameter of Heated Sample Core: 0.014m
Thickness of Disc (x): 0.0032m
Radial Position of Thermocouples:
T1=0.007m
T2=0.010m
T3=0.020m
T4=0.030m
3.5 Theory
3.5.1 Conduction Heat Transfer
When a temperature gradient exists in a body, there is an energy transfer from the high-
temperature region to the low-temperature region. The energy is transferred by conduction and
that the heat-transfer rate per unit area is proportional to the normal temperature gradient.
3.5.2 Radial Systems
3.5.2.1 Cylinders
Consider a long cylinder of inside radius r
i
, outside radius r
o
, and length L, such as the one
shown in Figure 2.1.We expose this cylinder to a temperature differential T
i
−T
o
. For a cylinder
37
with length very large compared to diameter, it may be assumed that the heat flows only in a
radial direction, so that the only space coordinate needed to specify the system is r. Again,
Fourier’s law is used by inserting the proper area relation. The area for heat flow in the
cylindrical system is
A
r
=2πrL
So that Fourier’s law is written
q
r
= −kA
r
q
r
= −2πkrL
Equation 3.1: Fourier Law equation for cylinders
Figure 3.1: Heat transfer
through cylinder
Figure 3.2: Temperature distribution in cylinder
With the boundary conditions
T=T
i
at r=r
i
T=T
0
at r=r
0
The solution to Equation 3.1 is
q=
Equation 3.2: Fourier Law equation for cylinders
3.6 Procedure
1. Ensure that the main switch is in the off position (the digital displays should not be
illuminated).
38
2. Ensure the cold water supply and electrical supply is turned on at the source. Open the
water tap until the flow through the drain hose is approximately 1.5 liters/minute.
3. Turn on the main switch and the digital displays should illuminate. Set the temperature
selector switch to T1 to indicate the temperature of the heated centre of the disc.
4. Following the above procedure ensure cooling water is flowing and then set the heater
voltage V to approximately 50 volts.
5. Monitor temperatures T1, T2, T3, T4, T5, and T6 until stable. When the temperatures
are stabilized record: T1, T2, T3, T4, T5, T6, V, I
6. Reset heater voltage to 100 volts and repeat the above procedure again and Monitor
temperatures T1, T2, T3, T4, T5, and T6 until stable. When the temperatures are
stabilized record: T1, T2, T3, T4, T5, T6 V, I. Repeat procedure with the difference of
50 V voltage
3.7 Observations
Sample
No.
T
1
T
2
T
3
T
4
T
5
T
6
V
I
⁰C
⁰C
⁰C
⁰C
⁰C
⁰C
Volts
Amps
1
2
3
4
Radius
0.007
0.010
0.020
0.030
0.040
0.050
---
---
Table 3.1: Distribution of temperature for different voltages
3.8 Calculated Data
3.8.1 Objective
To identify a given sample (disc material) by determining its thermal conductivity.
39
Sample No.
π
π
π
Watts
W/mK
W/mK
W/mK
1
2
3
4
Table 3.2: Thermal conductivity of given sample
3.8.1.1 Specimen Calculations
X=0.0032 (Thickness or length of disc)
Heat transfer rate from the heater;
From Fourier’s equation (ignoring the negative sign)
°
π
°
Examining the points T1 and T6 and substituting values gives
Similarly, the other pair of points on Radius;
π
π
3.8.1.2 Conclusion
40
3.8.1.3 Graph
Plot a graph b/w Radius from heated disc centre (x-axis) and Temperature (y-axis).
3.9 Statistical Analysis
For Thermal conductivity
% Error=
x
avg
=
S
x
=
3.10 Questions
1) How temperature distribution through the wall of a thick cylinder
2) What is steady-state heat transfer?
3) What is effect of changing the thickness of cylinder on thermal conductivity?
4) Why by increasing input heat Q, overall slope of the temperature gradients increases.
3.11 Comments
41
4. LAB SESSION 4
To verify laws of radiation by using shape factor
4.1 Learning Objectives
1) To verify the inverse square law for thermal radiation
2) To verify the Stefan Boltzmann Law
4.2 Apparatus
Radiation Heat Transfer unit H111C (Serial no H111C/01310)
4.3 Main Parts
1) Heat Source
2) Radiation detector
3) Temperature Sensors
4) Radiometer output unit
5) Main digital Control panel (H111)
4.4 Useful Data
Laws of radiant heat transfer and radiant heat exchange (H111C)
Stefen-Boltzman Constant =
4.5 Theory
4.5.1 Radiation
Radiation is the emission or transmission of energy in the form of waves or particles through
space or through a material medium.
4.5.2 Radiation Heat Transfer
Thermal radiation is electromagnetic radiation generated by the thermal motion of charged
particles in matter. All matter with a temperature greater than absolute zero emits thermal
radiation. When the temperature of the body is greater than absolute zero, interatomic collisions
cause the kinetic energy of the atoms or molecules to change. All bodies radiate energy in the
form of photons moving in a random direction, with random phase and frequency. When
radiated photons reach another surface, they may be absorbed, reflected or transmitted. The
behavior of a surface with radiation incident upon it can be described by the following
quantities:
= absorptance =fraction of incident radiation absorbed
Ρ= reflectance = fraction of incident radiation reflected
= transmittance = fraction of incident radiation transmitted.
42
4.5.3 Inverse square law
Intensity is inversely proportional to the square of the distance from the source of that
physical quantity. Mathematically formulated:
Intensity∝
4.5.4 Stefan–Boltzmann law
To show that the intensity of radiation varies as the fourth power of the source temperature.
The Stefan-Boltzmann law states that for a black body
-
Equation 4.1: Stefan-Boltzmann law
Where
= The energy emitted per unit area of a black body radiator
= The absolute temperature of the black body K
= The absolute temperature of the surroundings K
σ = Stefan-Boltzmann Constantσ =
This is the energy emitted from the surface.
At a distance x from the surface the energy received (and indicated) by a detector R will be
related to the Stefan-Boltzmann constant by a factor F such that.
4.6 Procedure
1. Ensure that the H111 main switch is in the off position (the three digital displays should
not be illuminated).
2. Turn the voltage controller anti-clock wise to set the AC voltage to minimum.
3. Install the heated plate at the left-hand side of the track and install the radiometer on
the right-hand carriage. No items are installed in the left-hand carriage for the
experiment but one of the black plates should be placed on the bench and connected to
the thermocouple socket T9.
4. Fit the light radiometer to the sensor carriage
5. Ensure that the radiation shield is in position in the radiometer aperture and station the
radiometer in the 900mm position
6. The radiometer should be left for several minutes after handling with the radiation
shield in position to ensure that residual heating has dissipated.
43
7. For radiometer experiments, position the
displays console on top of the H111
console. Connect the power cable between both consoles and plug the radiometer signal
cable into the front panel.
8. Turn on the H111 main switch and three digital displays should illuminate. The
radiometer should also illuminate. The required temperature is displayed on the LED
digital display by turning the rotary sector switch.
9. ‘Auto-Zero’ the radiometer by pressing the right hand * button twice.
Figure 4.1: Schematic diagram of experiment
10. Rotate the voltage controller clockwise to increase the voltage.
11. Monitor the
digital displays and after several minutes, the display should reach a
minimum.
12. Finally, “Auto-Zero” the radiometer by pressing the right hand * button twice.
13. Leave the radiation shield in position and rotate the voltage controller clockwise to
increase the voltage to maximum volts. Select the T
10
position on the temperature
selector switch and monitor the T
10
temperature.
14. When the T
10
temperature has reached a maximum condition, remove the radiation
shield (without touching the radiometer). Immediately the indicated value should start
to rise. Monitor the digital display until the displayed value reaches a maximum and
then record the following.
T
7
, T
10
, X (900mm in this case), R.
15. Again, without touching the radiometer, move the carriage holding the radiometer to a
position 800mm from the heated plate. Again, the radiometer reading will start to rise.
Allow this to reach a maximum and repeat the observations
T
7
, T10, X (800mm in this case), R.
44
16. Repeat the above procedure in reducing steps of 100mm until the radiometer is 200mm
from the heated plate.
4.7 Observations:
Sample test results
For the unit tested C = 0.786
Table 4.1: Measurement of temperatures from radiometer
While
T
7
= Temperature of black body
T
10
= Temperature of heater
X=Distance of radiometer from heater
V= Voltage
I= Current
R= Reading of radiometer in
R
c=
Corrected radiometer reading=
4.8 Calculated Data
4.8.1 Objective:01
To verify the inverse square law for thermal radiation
V
I
T
7
T
10
x
R
900
800
700
600
500
400
300
200
45
Table 4.2: Calculation of intensity of radian
The data may either be converted to
format as shown above and then plotted on a linear
graph or alternatively if log-log graph paper is available, the data may be plotted directly
without taking log values.
4.8.1.1 Graph
Plot a graph b/w log
10
x and log
10
Rc
4.8.1.2 Conclusion
4.8.2 Objective:02
To verify the Stefan Boltzmann Law
Table 4.3: Calculation of shape factor
4.8.2.1 Specimen Calculation
For the first sample the calculations are as follows:
T
a
= T
9
+ 273.15 T
s
= T
10
+273.15 While T
9
= ambient temperature
x
Log
10
x
Log
10
900
800
700
600
500
400
300
200
46
Hence
-
From the radiometer reading:
C x R (
)
Hence
It may be seen from the test results that the factor F remains essentially constant thereby
demonstrating that the Steffen-Boltzmann relationship applies.
4.8.2.2 Conclusion
4.9 Statistical Analysis
For Shape Factor F
x
avg
=
S
x
=
4.10 Questions
1) What is value of Log
10
x corresponding to the value of 550 mm, Calculate from graph
2) How does thermal radiation differ from other types of electromagnetic radiation?
3) What is inverse square law for thermal radiation
4) Define absorptivity, reflectivity and transmissivity
5) What is the Stefan-Boltzmann law?
4.11 Comments
47
5. LAB SESSION 5
To verify the role of shape factor involved in radiation heat transfer
5.1 Apparatus
Radiation Heat Transfer unit H111C (Serial no H111C/01310)
5.2 Main Parts
1) Heat Source
2) Radiation detector
3) Temperature Sensors
4) Radiometer output unit
5) Main digital Control panel (H111)
5.3 Useful Data
Laws of radiant heat transfer and radiant heat exchange (H111C)
Stefen-Boltzman Constant =
5.4 Theory
5.4.1 Radiation
Radiation is the emission or transmission of energy in the form of waves or particles through
space or through a material medium.
5.4.2 Shape Factor
It can be shown that the view factor F is related to the view angle such that
Figure.5.1: Schematic diagram for shape factor
48
Hence
θσ
-
θ
Equation 5.1: Energy received by detector
Test data is shown overleaf to illustrate the relationship.
5.5 Procedure
1. Install the heated plate at the left-hand side of the track and install the radiometer on
the right-hand carriage. No items are installed in the left-hand carriage for the
experiment but one of the black plates should be placed on the bench and connected to
the thermocouple socket T9
2. Fit the light radiometer to the sensor carriage.
3. Ensure that the radiation shield is in position in the radiometer aperture and station the
radiometer in the 900mm position
4. The radiometer should be left for several minutes after handling with the radiation
shield in position to ensure that residual heating has dissipated.
5. For radiometer experiments, position the
displays console on top of the H111
console. Connect the power cable between both consoles and plug the radiometer signal
cable into the front panel.
6. Turn on the H111 main switch and three digital displays should illuminate. The
radiometer should also illuminate. The required temperature is displayed on the LED
digital display by turning the rotary sector switch.
7. ‘Auto-Zero’ the radiometer by pressing the right hand * button twice.
Figure 5.2: Schematic diagram of experiment
8. Rotate the voltage controller clockwise to increase the voltage.
49
9. Monitor the
digital displays and after several minutes, the display should reach a
minimum.
10. Finally, “Auto-Zero” the radiometer by pressing the right hand * button twice.
11. Leave the radiation shield in position and rotate the voltage controller clockwise to
increase the voltage to maximum volts. Select the T
10
position on the temperature
selector switch and monitor the T
10
temperature.
12. When the T
10
temperature has reached a maximum condition, remove the radiation
shield (without touching the radiometer). Immediately the indicated value should start
to rise. Monitor the digital display until the displayed value reaches a maximum and
then record the following.
T
7
, T
10
, X (900mm in this case), R.
13. Again, without touching the radiometer, move the carriage holding the radiometer to a
position 800mm from the heated plate. Again, the radiometer reading will start to rise.
Allow this to reach a maximum and repeat the observations
T
7
, T10, X (800mm in this case), R.
14. Repeat the above procedure in reducing steps of 100mm until the radiometer is 200mm
from the heated plate.
5.6 Observations:
Sample test results
For the unit tested C = 0.786
Table 5.1: Measurement of temperatures from radiometer
While
T
7
= Temperature of black body
V
I
T
7
T
10
x
R
900
800
700
600
500
400
300
200
50
T
10
= Temperature of heater
X=Distance of radiometer from heater
V= Voltage
I= Current
R= Reading of radiometer in
R
c=
Corrected radiometer reading=
5.6.1 Calculated Data
Table 5.2: Radiation incident on the detector
5.6.1.1 Specimen Calculation
For the first data point at x = 900mm
+273.15
+273.15
Hence
σ
From the geometry θ
Hence
θ
From this data R
c
= q
b
. sin
2
θ
The corrected radiation
recorded by the radiometer under these conditions was
Ts
Ta
(Theoretical)
(Experimental)
K
K
Radians
51
= ( )
Comparing the calculated radiation incident on the detector
and the corrected
radiation measured by the detector
it may be seen that the value are similar.
Note that small errors in temperature measurement affect the data to the fourth power i.e.
5.6.1.2 Conclusion
5.7 Statistical Analysis
NA
5.8 Questions
1) What is a gray body
2) What is meant by the radiation shape factor?
3) What is radiation shields and its effect
5.9 Comments
52
6. LAB SESSION 6
To calculate the total heat transfer of combined convection and radiation heat transfer
mechanism
6.1 Learning Objective
[i] Determination of the combined (radiation and convection) heat transfer (
+
) from
a horizontal cylinder.
6.2 Apparatus
Combined Convection and Radiation Heat Transfer unit H111D (Serial No= H111D/01641)
6.3 Main Parts
1) Heater Power
2) T10 Heater surface temperature
3) Air velocity sensor (Hot wire anemometer)
4) T9 Air temperature
5) Throttle butterfly
6) Fan
7) Main Switch
8) Main digital Control panel (H111)
6.4 Useful Data
Combined Convection and Radiation H111D
T
ν
k
Pr
K
/s
w/mK
_
300
1.568E-05
0.02624
0.708
350
2.076 E-05
0.03003
0.697
400
2.590 E-05
0.03365
0.689
450
2.886 E-05
0.03707
0.683
500
3.790 E-05
0.04038
0.680
550
4.434 E-05
0.04360
0.680
600
5.134 E-05
0.05659
0.680
Table 6.1: Table of Physical properties of Air at Atmospheric Pressure
The above data is presented graphically on Graphs D1, D2, and D3.
If spreadsheet is to be utilized for data evaluation, then the values may be determined
with reasonable accuracy from the following equations.
Where T is the air temperature in K
Cylinder diameter D = 0.01m
Cylinder heated length L = 0.07m
53
Cylinder effective heated area A
s
= 0.0022
Effective air velocity local to cylinder due to blockage effect U
e
= U
a
X 1.22
6.5 Theory
When a horizontal cylinder, with its surface at a temperature above that of its surroundings, is
located in stationary air, the heat loss from the cylinder will be a combination of natural
convection to the air (air surrounding the cylinder becomes less dense and rises when it is
heated) and radiation to the surroundings.
Heat loss due to conduction is minimized by the design of the equipment and measurements
mid-way along the heated section of the cylinder can be assumed to be unaffected by
conduction at the ends of the cylinder. Heat loss by conduction would normally be included in
the analysis of a real application.
The following theoretical analysis uses an empirical relationship for the heat transfer due to
natural convection proposed by WH McAdams in the publication "Heat Transmission", third
edition, McGraw-Hill, New York, 1959.
Total heat loss from the cylinder: Q
total
= Q
c
+ Q
r
Equation 6.1
Heat loss due to natural convection: Q
c
= h
c
A
s
(T
s
- T
a
)
Equation 6.2
Heat loss due to radiation: Qr = h
r
A
s
(T
s
- T
a
)
Equation 6.3
Heat transfer area (surface area): A
s
= (π D L)
Equation 6.4
The heat transfer coefficients h
c
and h
r
can be calculated using the following relationships
h
c
=1.32
Equation 6.5
h
r
=ϵϭ
Equation 6.6
ϭ= Stefan Boltzmann constant
Є = Emissivity of surface (dimensionless)
Ts = Surface temperature of cylinder (K)
Ta = Ambient temperature (K)
6.6 Procedure
1. Turn the voltage controller anti-clock wise to set the AC voltage to minimum. Ensure
the Combined Convection and Radiation H111D accessory has been connected to the
Heat Transfer Service Unit H111.
2. Ensure that the heated cylinder is located in its holder at the top of the duct and that the
cylinder is rotated so that the thermocouple location is on the side of the cylinder.
54
3. Turn on the main switch and the digital displays should illuminate. Turn the rotary
selector switch to display T
10
. Rotate the voltage control clockwise to increase the
voltage. Note that for natural convection experiments are to be undertaken it is
recommended that the cylinder surface temperature
is NOT allowed to exceed
500.
4. Rotate the voltage controller to give a 50-volt reading.
5. Select the temperature position T
10
using the rotary selector switch and monitor the
temperature.
6. Open the throttle butterfly on the fan intake but do not turn on the fan switch, as the fan
will not be used for natural convection.
7. When T
10
has reached a steady state, temperature record the following T
9
, T
10
, V, I.
8. Increase the voltage controller to give an 80-volt reading, monitor T
10
for stability and
repeat the readings.
9. Increase the voltage controller to give a 120-volt reading, monitor T
10
for stability and
repeat the readings.
10. Increase the voltage controller to give a 150-volt reading, monitor T
10
for stability and
repeat the readings for different voltages
Figure 6.1: Schematic Diagram of Experiment
55
6.7 Calculated Data
6.7.1 Objective:01
Determination of the combined (radiation and convection) heat transfer (
+
) from a
horizontal cylinder.
6.7.1.1 Observations
Sample test results
Sample
V
I
T
9
T
10
-
Volts
Amps
1
2
3
4
5
Table 6.2: Measurement of temperature for free convection
T
9
= Ambient Temperature
T
10
= Heater temperature
V= Input voltage
I= Input current
Sample
-
W
W
W
W
1
2
3
4
5
Table 6.3: Heat transfer due to free convection and radiation
6.7.1.2 Specimen Calculations
For the first sample the calculation are as follows:
For the radiant component;
56
Hence the heat lost to radiation
(
is obtained from USEFUL DATA on)
For the convective component using the simple formula
Hence the heat lost to convection;
(
Is obtained from USEFUL DATA)
= h
c
A
s
(T
s
-T
a
)
Hence the total heat lost by calculation
= (W)
In addition it may be seen that at low temperatures the convective component of heat transfer
is predominant while at higher temperatures the radiant component becomes predominant.
The temperature, at which the conditions reverse, is also influenced by the emissivity of the
surface, and that of the surroundings.
6.7.1.3 Graph
Draw the Graph of h
c
, h
r
(y-Axis) and surface Temperature T
10
(X- Axis)
6.7.1.4 Conclusion
57
6.8 Statistical Analysis
For total heat transfer in free convection
x
avg
=
S
x
=
6.9 Questions
1) Write about the trend of convective heat transfer coefficient with heater temperature
2) What is value of heater temperature at air velocity of 2.3 m/s, compute it from graph.
3) Write about the trend of Radiant heat transfer coefficient with heater temperature
6.10 Comments
58
7. LAB SESSION 7
To calculate the total heat transfer of combined “forced convection” and “radiation” heat
transfer mechanism
7.1 Learning Objective
[i] Determination of the effect of forced convection on the heat transfer from a cylinder at
varying air velocities.
7.2 Apparatus
Combined Convection and Radiation Heat Transfer unit H111D (Serial No= H111D/01641)
7.3 Main Parts
1) Heater Power
2) T
10
Heater surface temperature
3) Air velocity sensor (Hot wire anemometer)
4) T
9
Air temperature
5) Throttle butterfly
6) Fan
7) Main Switch
8) Main digital Control panel (H111)
7.4 Useful Data
Combined Convection and Radiation H111D
T
ν
k
Pr
K
/s
w/mK
_
300
1.568E-05
0.02624
0.708
350
2.076 E-05
0.03003
0.697
400
2.590 E-05
0.03365
0.689
450
2.886 E-05
0.03707
0.683
500
3.790 E-05
0.04038
0.680
550
4.434 E-05
0.04360
0.680
600
5.134 E-05
0.05659
0.680
Table 7.1: Table of Physical properties of Air at Atmospheric Pressure
The above data is presented graphically on Graphs D1, D2, and D3.
If spreadsheet is to be utilized for data evaluation then the values may be determined
with reasonable accuracy from the following equations.
Where T is the air temperature in K
Cylinder diameter D = 0.01m
Cylinder heated length L = 0.07m
59
Cylinder effective heated area A
s
= 0.0022
Effective air velocity local to cylinder due to blockage effect U
e
= U
a
X 1.22
7.5 Theory
7.5.1 Forced convection
Forced convection is a mechanism, or type of transport in which fluid motion is generated by
an external source (like a pump, fan, suction device, etc.). It should be considered as one of the
main methods of useful heat transfer as significant amounts of heat energy can be transported
very efficiently.
Actual power supplied to the heated cylinder Qin = V I (Watts) Equation 7.1
Qr = h
r
A
s
(T
s
- T
a
)
So Nusselt number is
]
Equation 7.2
And Reynolds number is
Equation 7.3
Equation 7.4
This results in a convective heat transfer of
Equation 7.5
Hence the total heat transfer from the cylinder
Equation 7.6
7.6 Procedure
1. Ensure that the heated cylinder is located in its holder at the top of the duct and that the
cylinder is rotated so that the thermocouple location is on the side of the cylinder. This
is shown schematically below.
2. Turn on the main switch and the digital displays should illuminate. Turn the rotary
selector switch to display T
10
. Rotate the voltage control clockwise to increase the
voltage.
3. Rotate the voltage controller to give a 50-volt reading.
4. Select the temperature position T
10
using the rotary selector switch and monitor the
temperature.
5. Open the throttle butterfly on the fan intake and turn on the fan switch,
60
6. When T
10
has reached a steady state, temperature record the following T
9
, T
10
, V, I.
7. Increase the voltage controller to give an 80-volt reading, monitor T
10
for stability and
repeat the readings.
8. Increase the voltage controller to give a 120-volt reading, monitor T
10
for stability and
repeat the readings.
9. Increase the voltage controller to give a 150-volt reading, monitor T
10
for stability and
repeat the readings.
10. Finally increase the voltage controller to give approximately a 185-volt reading,
monitor T
10
for stability and repeat the readings. However, the temperature of the
cylinder should not be allowed to exceed 500 and if local conditions result in a higher
temperature the voltage should be reduced accordingly.
Figure 7.1: Schematic Diagram of Experiment
61
7.6.1 Objective
Determination of the effect of forced convection on the heat transfer from a cylinder at
varying air velocities.
7.6.1.1 Observations
Sample test results
Sample
V
I
T9
T10
-
Volts
Amps
1
2
3
4
5
Table 7.2: Measurement of temperature due to forced convection
T
9
= Ambient Temperature
T
10
= Heater temperature
V= Input voltage
I= Input current
7.6.1.2 Calculated Data
Calculation results in the following parameters
Sample
Pr
k
R
e
N
u
-
W
m/s
W
-
-
1
2
3
4
5
Sample
-
W
W
W
1
2
3
4
5
Table 7.3: Heat transfer due to forced convection
7.6.1.3 Specimen Calculations
For the first sample the calculations are as follows
(W)
For the radiant component
62
This results in a radiant heat transfer of
For the above convective component using the formula
First the physical parameters must be determined at the air stream temperature T9
From the graphs D1, D2, D3 for example at T
9
=296K
The measured duct velocity s locally increased around the cylinder to (effective air
velocity) due to the blockage effect of the cylinder itself. This relates to the area ratio between
the duct cross sectional area and the plan area of the cylinder in the duct.
(m/s)
Hence
Hence substituting the values in the equation;
From the Nusselt number ;
This results in a convective heat transfer of
Hence the total heat transfer from the
cylinder
63
7.6.1.4 Graph:
If the surface temperature T
10
is plotted against the effective air velocity Ue it may be seen that
for a constant heat input the surface temperature falls as the velocity increases.
7.6.1.5 Conclusion
7.7 Statistical Analysis
For total heat transfer in forced convection
x
avg
=
S
x
=
7.8 Questions
1) What is free and forced convection
2) What is drag coefficient
7.9 Comments
64
Graph 1
Graph 7.1: Kinematic velocity of air at standard Pressure
65
GRAPH# D2
Graph 7.2: Thermal conductivity of air at standard pressure
66
GRAPH# D3
Graph 7.3: Prandtl number of air at standard pressure
67
8. LAB SESSION 8
To experimentally verify the heat transfer from an extended surface from combined modes of
free conduction, free convection and radiation heat transfer by comparing it with the theoretical
analysis
8.1 Learning Objective
To analyse the increase in heat transfer by using extended surface body
8.2 Apparatus
Extended Surface Heat Transfer unit H111E (Serial no H111E/00832)
8.3 Main Parts
1) Heated cylinder
2) Eight temperature sensors (Thermocouples)
3) Heater
4) Heat transfer service unit (H111)
8.4 Useful Data
1) HEATED ROD Diameter
2) Heated rod length
3) Heated rod effective cross-sectional area
4) Heated rod surface area
5) Thermal conductivity of heated rod material
6) Stefan Boltzmann constant
8.5 Theory:
8.5.1 Fin (extended surface)
In the study of heat transfer, fins are surfaces that extend from an object to increase the rate of
heat transfer to or from the environment by increasing convection. The amount of conduction,
convection, or radiation of an object determines the amount of heat it transfers. Increasing the
temperature gradient between the object and the environment, increasing the convection heat
transfer coefficient, or increasing the surface area of the object increases the heat transfer.
Sometimes it is not feasible or economical to change the first two options. Thus, adding a fin
to an object, increases the surface area and can sometimes be an economical solution to heat
transfer problems.
The heat Transferred can be calculated at a given point x
Equation 8.1: Heat transferred through extended
surface
While
Q
x
=Heat transferred at a given point x
T
x
=Temperature at a given point x
68
T
a=
Ambient temperature
L= Length of rod
h=Overall heat transfer coefficient
P= Perimeter
K= Thermal conductivity
A= Heated rod surface area
8.6 Procedure:
1. Turn the voltage controller anti-clock wise to set the AC voltage to minimum. Ensure the
Extended Surface Heat Transfer Unit H111E accessory has been connected to the Heat
Transfer Service Unit H111.
2. After adjusting the heater voltage ensure that T1 (the thermocouple closest to the heater)
varies in accordance with the sense of adjustment. i.e. if the voltage is increased the
temperature T1 should also increase, if the voltage is reduced the temperature T1 should be
reduce.
3. It is now necessary that to monitor the temperature T1 to T8 until all the temperatures are
stable.
4. When T1 through T8 have reached a steady state, temperatures record the following. T1 to
T9, V and I.
5. If time permits increase the voltage to a 120volts reading, repeat the monitoring of all
temperatures and when stable repeat the above readings.
6. When the experimental procedure is completed, it is good practice to turn off the power to
the heater by reducing the AC voltage to zero and leaving the fan running for a short period
until the heated cylinder has cooled. Then turn off the main switch.
69
Figure 8.1: Schematic Diagram of Experiment
8.7 Observations
Sample No
V
-
-
I
-
-
t
1
0
t
2
0.05
t
3
0.1
t
4
0.15
t
5
0.2
t
6
0.25
t
7
0.3
t
8
0.35
t
9
-
Table 8.1: Temperatures measured at different distances from T1
70
8.8 Calculated Data
W
Calculated
heat
transferred
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
Table 8.2: Heat transfer from extended surface
8.8.1 Specimen Calculation
For the first sample the calculations are as follows
(W)
The value of h will be that due to both convective and radiation heat transfer
For the radiant component;
=
Where Stefan Boltzmann Constant = 5.67 ×
F = Shape factor or view factor (relating to the element geometry and the surroundings)
ε = Emissivity of the rod surface = 0.95
= Absolute ambient temperature t
9
+ 273.15K
= Absolute mean of the measured surface temperature of the rod.
For the convective component;
71
This is a simplified empirical equation for natural convection from a horizontal cylinder. Where
= Absolute mean of the measured surface temperature of the rod.
= Diameter of the rod
Hence the overall estimated heat transfer coefficient
=
Now m can be determined to a reasonable degree of accuracy such that
Where P is the perimeter of the rod = π D
Now the heat Transferred can be calculated at a given point x;
While Tan h (mL) =
And Cos h (mL)=
Note: For insulated fin tip and negligible heat loss from fin tip
Should be equal to
8.8.2 Graph
Draw the graph b/w the distance from T1 thermocouple (X-Axis) and Temperature (Y-Axis).
8.8.3 Conclusion
8.9 Questions
1) How heat transfer is varied by varying heat transfer area
2) What is effect of perimeter on heat transfer
3) At which position, the temperature reaches the maximum value, give reason.
8.10 Comments
72
9. LAB SESSION 9
To Reduce radiation errors in measurement of temperature by using shield between sensor
and source of radiation
9.1 Learning Objective
1) To reduce the errors in temperature measurement due to radiation from a source by
using radiation shield between the sensor and the source of radiation.
9.2 Apparatus
Radiation Errors in temperature Measurements H111F (Serial no H111F/00315)
9.3 Main Parts
1) Radiant Source
2) Temperature Sensors
3) Shields of different grades
4) Main digital Control panel (H111)
9.4 Theory
The objective for the temperature sensors is to accurately measure the temperature of the air
stream. In order to do this the sensors must stabilize at the same temperatures as the air stream.
Under ideal conditions the sensors will gain or lose heat until stabilization occurs and the
sensors are at the same temperature as the air. However, if a source of thermal radiation is
visible to the sensor then depending upon the emissivity of the sensor and the source more or
less energy may be absorbed by the sensor. Hence the sensor may stabilize at a temperature
above or below the temperature of the air depending upon the temperature of the radiant source.
The magnitude of the difference in sensor temperature relative to the air stream will depended
upon several factors.
➢ The difference in temperature between the sensor and the radiating surface.
➢ The velocity of the air passing the sensor.
➢ The size of the sensor.
➢ The emissivity of the sensor, the surroundings and the radiant source.
➢ The thermal conductivity of the sensor material and its connecting lead.
➢ Other material that may be in the air stream such as dust or water vapor.
If a suitable shield can be placed between the radiant source and the thermocouple the errors
in measurement can be reduced. Though the shield will be heated or cooled by the radiant
source the temperature reached by the shield will have less influence on the thermocouple then
73
that of the radiant source. In the apparatus, the shield is a polished stainless steel plate that can
be lowered between the ceramic heater and the three test thermocouples. The shield allows air
to pass through but prevents direct line of sight influence from the radiant source
9.5 Procedure:
1. Turn the voltage controller anti-clock wise to set the AC voltage to minimum. Ensure the
Radiation Errors H111F accessory has been connected to the Heat Transfer Service Unit
H111.
2. Ensure that the radiation shield is not fitted.
3. Turn on the main switch and the digital displays should illuminate. Select the temperature
position T10 using the rotator switch and monitor the temperatures regularly.
4. Set the temperature selector switch to display temperatures T6, T7, T8, T9 and T10 and
record the values.
5. Open the throttle butterfly but do not turn on the centrifugal fan at this point.
6. Rotate the voltage controller clockwise to increase the heater voltage to 80 Volts. Select
the T10 position on the temperature selector switch and monitor the T10 temperature. Also
monitor temperatures T7 to T9 until these reach a stable temperature (Note that the
temperatures may not be equal).
7. When the temperatures are stable record T6, T7, T8, T9, T10, V, and I.
8. Rotate the voltage controller clockwise to increase the heater voltage to 120 Volts. Again
allow the temperatures to stabilize and then record T6, T7, T8, T9, T10, V, and I.
9. Repeat the above procedure at heater voltages of 180 and 230 volts (Note that the heater
temperature T10 should not be allowed to exceed 400).
10. Completely close the throttle butterfly on the fan intake and then turn on the centrifugal
fan.
11. Adjust the throttle until a velocity of approximately 0.5m/s is indicated.
12. Observe the temperature T6 to T10 and when stable record T6, T7, T8, T9, T10, V, and I.
13. Increase the air velocity to 1m/s, allow the temperatures to stabilize and repeat the
observations. Further increase the velocity to 2m/s and 4m/s and again repeat the
observations.
14. Repeat all the procedure for objective 2 by using the radiation shield.
9.6 Observations
74
9.6.1 Objective
To demonstrate how temperature measurements can be affected by radiant heat transfer to a
sensor from its surroundings
Table 9.1: Temperatures at different points from radiant source
While
V= Voltage
WITHOUT FAN ASSISTED AIR FLOW
V
I
T6
T7
T8
T9
T10
1
No Shield
0
Shield
0
2
No Shield
0
Shield
0
3
No Shield
0
Shield
0
4
No Shield
0
Shield
0
5
No Shield
0
Shield
0
WITH FAN ASSISTED AIR FLOW
1
No Shield
Shield
2
No Shield
Shield
3
No Shield
Shield
4
No Shield
Shield
75
I= Current, T6= Temperature of air and T7, T8, T9= Temperature at different points
T
10
= Temperature of heater
= Air velocity
9.6.1.1 Graph
i) Draw the graph b/w heater volts (V) along x-Axis and Temperature T6, T7, T8,
T9 along Y-Axis. (i.e. V vs T6, V vs T7, V vs T8, V vs T9, V vs T10) with shield
and without shield
9.6.1.2 Conclusion
9.7 Comments
76
10. LAB SESSION 10
To determine the Convective heat transfer coefficient of a solid cylinder using analytical
transient temperature/heat flow charts
10.1 Learning Objective
1) Use of heisler charts for lumped heat capacity system
2) Use of properties like biot number and fourier number to calculate convective heat
transfer unit
10.2 Apparatus
Heat Transfer service unit with Unsteady State Heat Transfer Unit H111G
10.3 Main Parts
1) Drain Valve
2) Water supply
3) Pump
4) 20mm diameter Brass cylinder
5) Temperature sensors prob
6) water bath
7) 20 mm diameter stainless steel cylinder
10.4 Theory
10.4.1 Transient Heat-Transfer
If a solid body is suddenly subjected to a change in environment, some time must elapse before
an equilibrium temperature condition will prevail in the body. In the transient heating or
cooling process that takes place in the interim period before equilibrium is established, the
analysis must be modified to take into account the change in internal energy of the body with
time, and the boundary conditions must be adjusted to match the physical situation that is
apparent in the unsteady-state heat-transfer problem. Unsteady-state heat-transfer analysis is
obviously of significant practical interest because of the large number of heating and cooling
processes that must be calculated in industrial applications
10.4.2 Lumped-Heat-Capacity System
Transient heat conduction can be analyzed in systems that may be considered uniform in
temperature. This type of analysis is called the lumped-heat-capacity method. Such systems
are obviously idealized because a temperature gradient must exist in a material if heat is to be
conducted into or out of the material. In general, the smaller the physical size of the body, the
more realistic the assumption of a uniform temperature throughout; in the limit a differential
volume could be employed as in the derivation of the general heat-conduction equation
10.4.3 Biot number (Bi)
The Biot number (Bi) is a dimensionless quantity used in heat transfer calculations. It is named
after the French physicist Jean-Baptiste Biot (1774–1862), and gives a simple index of the ratio
of the heat transfer resistances inside of and at the surface of a body. This ratio determines
77
whether or not the temperatures inside a body will vary significantly in space, while the body
heats or cools over time, from a thermal gradient applied to its surface. In general, problems
involving small Biot numbers (much smaller than 1) are thermally simple, due to uniform
temperature fields inside the body. Biot numbers much larger than 1 signal more difficult
problems due to non-uniformity of temperature fields within the object. It should not be
confused with Nusselt number, which employs the thermal conductivity of the fluid and hence
is a comparative measure of conduction and convection, both in the fluid.The Biot number has
a variety of applications, including transient heat transfer and use in extended surface heat
transfer calculations.
The Biot number is defined as
B
i
=
Equation 10.1: Biot number
h = film coefficient or heat transfer coefficient or convective heat transfer coefficient
L = characteristic length, which is commonly defined as the volume of the body divided
by the surface area of the body, such that L=
k = Thermal conductivity of the body
The physical significance of Biot number can be understood by imagining the heat flow from
a small hot metal sphere suddenly immersed in a pool, to the surrounding fluid. The heat flow
experiences two resistances: the first within the solid metal (which is influenced by both the
size and composition of the sphere), and the second at the surface of the sphere. If the thermal
resistance of the fluid/sphere interface exceeds that thermal resistance offered by the interior
of the metal sphere, the Biot number will be less than one. For systems where it is much less
than one, the interior of the sphere may be presumed always to have the same temperature,
although this temperature may be changing, as heat passes into the sphere from the surface.
The equation to describe this change in (relatively uniform) temperature inside the object is
simple exponential one described in Newton's law of cooling.
In contrast, the metal sphere may be large, causing the characteristic length to increase to the
point that the Biot number is larger than one. Now, thermal gradients within the sphere become
important, even though the sphere material is a good conductor. Equivalently, if the sphere is
made of a thermally insulating (poorly conductive) material, such as wood, the interior
resistance to heat flow will exceed that of the fluid/sphere boundary, even with a much smaller
sphere. In this case, again, the Biot number will be greater than one.
10.4.4 Fourier number (Fo)
Fourier number (Fo) or Fourier modulus, named after Joseph Fourier, is a dimensionless
number that characterizes transient heat conduction. Conceptually, it is the ratio of diffusive or
conductive transport rate to the quantity storage rate, where the quantity may be either heat
(thermal energy) or matter (particles). The number derives from non-dimensionalization of the
heat equation (also known as Fourier's Law) or Fick's second law and is used along with the
Biot number to analyze time dependent transport phenomena.
The general Fourier number is defined as
78
F
o
=
Equation 10.2: Fourier
number
Equation 10.3:
Thermal diffusivity
α is the thermal diffusivity (SI units: m
2
/s)
t is the characteristic time (s)
L is the length through which conduction occurs (m)
K is thermal conductivity (W/(m·K))
ρ is density (kg/m³)
c is specific heat capacity (J/(kg·K))
10.4.5 Heisler charts
Heisler charts are a graphical analysis tool for the evaluation of heat transfer in thermal
engineering. They are a set of two charts per included geometry introduced in 1947 by M. P.
Heisler
.
which were supplemented by a third chart per geometry in 1961 by H. Gröber. Heisler
charts permit evaluation of the central temperature for transient heat conduction through an
infinitely long plane wall of thickness 2L, an infinitely long cylinder of radius r
o
, and a sphere
of radius r
o
.
Although Heisler-Gröber charts are a faster and simpler alternative to the exact solutions of
these problems, there are some limitations. First, the body must be at uniform temperature
initially. Additionally, the temperature of the surroundings and the convective heat transfer
coefficient must remain constant and uniform. Also, there must be no heat generation from the
body itself.
10.5 Procedure
1. Ensure that the residual current circuit breaker (RCCB) is open-circuit. Ensure that the
drain valve adjacent to the circulating pump is in the closed position and half-fill the
water bath with clean water.
2. Pump bleeding- Switch on the RCCB/MCB to cause the pump to run. Incline the pump
by lifting the baseboard from the front to allow the air to escape. Noise from the pump
is the sign of trapped air. A bleed screw is fitted to the head of the pump.
3. Continue the filling of bath until the water level is at mid height of the holes in the flow
duct. If the local water contains of a large amount of dissolved solids that normally
result in scale build up then it is recommended that the bath id fitted with de-ionized or
79
mineralized water. Ensue that the thermostat has been turned fully anti-clockwise and
is in the off position.
4. Ensure that the H111 unit main switch is in the off position (None of three digital
displays should be illustrated). Ensure that the residual current circuit breaker on the
H111 rear panel is in the ON position. Ensure that the residual current circuit breaker
on the H111G baseboard is in the on position. Not that the residual current circuit
breaker on the both units (H111 and H111G) should be tested for normal operation at
intervals specified by local regulations.
5. Turn on the power supply to the Unsteady State Heat Transfer unit and turn on the 16A
Heater miniature circuit breaker (MCB). Ensure that the red power indicator adjacent
to the thermostat is illustrated. Turn the thermostat to position 6 for faster heating. The
water will take approximately 30 minutes to heat from cold. At this setting the water
will boil, if left unattended. While the water bath is heating the following may be
auctioned.
6. Install the 20mm diameter brass cylinder in the shape carrier.
7. Insert the T3 probe to engage fully into the center of the shape.
8. Insert the T2 probe to sense water temperature adjacent to the shape.
9. Avoid touching the shape by hand to reduce thermal effects and place the shape on the
bench to reach ambient temperature.
10. The water bath temperature T1 should be stabilized at approximately 80 to 90˚C
11. Set the circulating pump to 3 and therefore the water flow velocity in the flow duct.
12. Turn on the power supply to the Heat Transfer Service Unit H111 and main switch and
three digital displays illustrate. Set the temperature selector switch to the T1to indicate
the temperature of the bath. Observe the T1 to confirm that it is slowly increasing as
the bath is heated.
13. Record the start conditions temperatures and then plunge the shapes in the flow duct.
Then record temperatures and time.
14. Observe the T1. If the bath temperature exceeds that is required, reduce the thermostat
setting to OFF and wait for the water to cool. The water bath temperature T1 should not
be allowed to exceed 85-90 as the pump will cavitate.
15. Once the 20mm diameter brass has reached the water bath temperature, remove it from
the tank install the 20mm stainless steel cylinder in the shape carrier.
16. Record the starting condition temperatures and then plunge the shape in the flow duct.
Then record temperatures and time.
17. Having achieved the desired temperature, say85, reduces the thermometer setting to
position 2. It will cycle ON/OFF to maintain the existing temperature.
18. If time permits the procedures may be repeated for the brass and stainless-steel sphere
and/or the Brass and Stainless Slab.
19. In addition, by varying the circulating pump speed, the effect of variation of water
velocity on local heat transfer coefficient may be investigated.
80
20. When the experimental procedure is completed, it is good habit to turn off the power to
the heater by reducing the AC voltage to zero. And fan leaving the fan running for a
short period until the heater has cooled. Then turn off the main switch.
10.6 Observations
Recorded Time
T1
Bath Temp.
T2
Air/ Water Temp.
T3
Geometric Centre Temp.
Seconds
ºC
ºC
ºC
0
5
10
15
20
25
30
35
40
Table 10.1: Specimen: 20mm diameter Brass Cylinder.
Recorded Time
T1
Bath Temp.
T2
Air/ Water Temp.
T3
Geometric Centre Temp.
Seconds
ºC
ºC
ºC
0
5
10
15
20
25
30
35
40
Table 10.2: Specimen: 20mm Stainless Steel Cylinder
81
10.7 Calculated Data
Recorded
Time
T1
Bath
Temperature
T3
Geometric
Centre
Temperature
θ
Non-
dimensional
Temperature
F
o
Fourier
Number
1/Bi
Inverse Biot
Number
(h)
Convective
heat
transfer
coefficient
Seconds
0
5
10
15
20
25
30
35
40
Table 10.3: Properties of Specimen: 20mm diameter Brass Cylinder
Recorded
Time
T1
Bath
Temperature
T3
Geometric
Centre
Temperature
θ
Non-
dimensional
Temperature
F
o
Fourier
Number
1/Bi
Inverse Biot
Number
(h)
Convective
heat
transfer
coefficient
Seconds
0
5
10
15
20
25
30
35
40
Table 10.4: Properties of Specimen: 20mm diameter stainless steel Cylinder
10.7.1 Sample Calculations
The calculation procedure for system with finite internal and surface heat transfer resistance is
as follows.
For each sample after intermission the non-dimensional temperature is calculated.
82
=
Similarly, the Fourier Number For non-dimensional time
Thermal diffusivity =
For brass from USEFUL DATA
=
=3.7
T =5 second
For cylinder the characteristics length=
Hence
=1.85
From the Heisler chart for a semi-infinite cylinder.
The co-ordinates for F
o
= and give
= the radius =
Hence for the brass cylinder where
This is the heat transfer coefficient around the cylinder due to the velocity of the hot water in
the flow duct. This velocity depends only upon the pump speed.
For the stainless-steel cylinder
Repeat same calculations for stainless steel cylinder
83
10.7.2 Graph
Draw graph between time (x-axis) and temperatures (y-axis)
10.7.3 Conclusion
10.8 Statistical Analysis
NIL
10.9 Questions
1) How the temperature is distributed at different interval of time
2) What is Fourier Number
3) What is Biot number
4) What is Transient Heat-Transfer
5) What is Lumped-Heat-Capacity System
6) How Geometric Centre Temp is distributed at different intervals of time
7) How Fourier number and Biot number vary with time. Give reason
10.10 Comments
84
85
11. LAB SESSION 11
To measure the effect of different exchanger geometry on convection heat transfer
mechanism
11.1 Learning Objective
1) Measure temperatures of different points in Free and forced convection in flat surfaces
2) Measure the dependence of the heat transmission on exchanger geometry.
11.2 Apparatus
Free and forced convection heat transfer unit TCLFC (Serial No= TCLFC 0009/07)
11.3 Main Parts
1) Stainless steel tunnel of rectangular section
2) Flat exchanger, tenon exchanger and fins exchanger
3) Thermocouple
4) fan supply
5) A branded computer attached to unit
6) Interface
11.4 Useful Data
• Structure of anodized aluminium that guarantees a good stability and resistance to the
environment.
• Stainless steel tunnel 700 mm long, painted and resistant to corrosion.
• Methacrylate viewer that allows a good visualization of the exchanger that is in use.
• Grey PVC stabilizers to guarantee a uniform air flux.
• Thermocouples type J.
• Maximum working temperature: 100ºC.
• Flow sensor with digital output.
• Aluminium exchangers of flat, spiked and bladed surfaces.
• Heating resistances of 150W.
Dimensions and weights
• Approximate dimensions of the equipment: 37x61x92
• Approx. shipment volume: 0.2m
3
• Approx. weight: 10 Kg
86
11.5 Theory
Convection is the term used for the process of energy transmission, which takes place in the
fluid mainly due to the energy transported by the movement of the fluid. The conduction
energy process by molecular exchange is, as logical, always present. However, big quantities
of energy (or heat) of the fluids are in contact with regions of inferior energy (colder regions)
due to the existence of big displacements of the fluid particles. If external forces in form of
difference of pressures produce the movement of the fluid, this mechanism is called forced
convection. An example of forced convection is the pumping of a fluid, in contact with solid
surfaces at different temperatures to that of the fluid. If no external forces are applied to a
fluid, it can move due to density differences that could be produced by a solid body
submerged in a fluid whose temperature is different to that of the fluid. This type of heat
exchange is called free
Convection and it can be observed in a recipient with boiling water, in the air that surrounds
radiators in rooms, etc. The following theoretical analysis uses an empirical relationship for
the heat transfer due to natural convection proposed by WH McAdams in the publication
"Heat Transmission", third edition, McGraw-Hill, New York, 1959
Heat loss due to natural convection: Q
c
= h
c
A
s
(T
s
- T
a
)
Equation 8.1
Heat transfer area (surface area): A
s
= (π D L)
Equation 8.2
The heat transfer coefficient h
c
can be calculated using the following relationships
h
c
=1.32
Equation 8.3
Ts = Surface temperature of cylinder (K)
Ta = Ambient temperature (K)
11.5.1 Introduction of The Equipment
Figure 8.1: Schematic Diagram of Experiment
Simultaneous heat transference by conduction and convection (free or forced) is the base of
several industrial heat exchangers, as well as the several devices related to them. This
87
equipment of EDIBON allows studying the efficiency of different exchangers, analyzing the
heat transmission coefficients of each of the exchangers exposed to different airflows. A fan
placed in the upper part of the tunnel allows
controlling the airflow that goes through the tunnel. An interface connectable to a PC contains
the control circuits to measure temperatures, electrical control, electrical supply and speed
control of the fan.
The interface provides an output to a PC where the values and graphics of all the variables
involved in the practices are shown. The airflow is measured with a flowmeter set on the
inferior part of the tunnel. This EDIBON equipment allows making a study of the heat
transmission in three different types of exchangers
1. Flat exchanger
2. Tenon exchanger
3. Fins exchanger
11.5.2 Description of The Equipment
The equipment consists of a stainless-steel tunnel of rectangular section supported by a
structure in anodized aluminium that allows to be set on the worktable. In the tunnel, three
types of different heat exchangers can be set: flat exchanger, tenon exchanger and fins
exchanger. Each exchanger has an electric
resistance for its heating. In the three bases of the exchangers we set a thermocouple that serves
to control the temperature that the exchangers reach. The heat exchanger that is used in each
moment can be observed by a methacrylate window placed in the opposite side of the tunnel
The rising air flux through the tunnel can be generated by a variable speed fan set on the
superior part. The airflow generated in the tunnel is measured by a flow meter placed in the
inferior part of the tunnel. By some air flux concentrators a correct distribution of the airflow
is guaranteed by the area of heat exchange. Two thermocouples measure the air temperature at
the inlet and outlet of the area of heat exchange. Temperature measurements, at different
distances of the base of the tenon and fins exchangers, are made by other five thermocouples
that are introduced by one side of the tunnel. These measurements allow observing the
gradients of temperature
in the longitudinal direction of the exchangers and in the direction of the air flux. An interface
receives the signal of all the thermocouples and the flow meter, providing a computerized outlet
of all the measurements. By the interface we make a control of temperature at the bases of the
exchangers. Besides, the fan supply and the electrical resistance are provided by the interface.
The electric supply of all the equipment is made by the connection of the interface to the net.
11.6 Objective: 1
To demonstrate the relationship between power input and surface temperature in free
convection
11.6.1 Procedure
1. We will start taking the measure of the surface that exchanges heat.
2. Next, we place the flat exchanger in the tower
3. We insert the thermocouples. A thermocouple will be placed in the exchanger, and the
other three in the three orifices placed in the middle of the tunnel.
4. The equipment is connected. The power of the resistance is regulated in fixed values.
88
5. When the temperatures are established we will proceed to its measurement, as well as
that of the air speed.
6. Once all the measures are taken the equipment is unplugged. When some time has gone
by, the thermocouples and the exchanger are removed
7. Repeat the experiment by turning the fan in “ON” position
11.6.2 Observations
Table 11.1: Temperatures in free convection
Table 11.2: Temperatures in forced convection
11.6.3 Graph
Draw the Graph of temperatures (y-Axis) and AR-1 (X- Axis) for free as well as in forced
convection
11.6.4 Conclusion
11.7 Objective: 2
No
AR-1
(Ohm)
SC-1
(l/s)
ST-1
(°C)
ST-2
(°C)
ST-3
(°C)
ST-4
(°C)
ST-5
(°C)
ST-6
(°C)
ST-7
(°C)
No
AR-1
(Ohm)
SC-1
(l/s)
ST-1
(°C)
ST-2
(°C)
ST-3
(°C)
ST-4
(°C)
ST-5
(°C)
ST-6
(°C)
ST-7
(°C)
89
Measure dependence of the heat transmission on exchanger geometry
11.7.1 Procedure
1. You will begin placing the blade exchanger in the tower. Next, the thermocouples are
introduced to measure the temperature in the base of the exchanger, that of the inlet air
and that of outlet.
2. Fix the electric power of the resistance and the speed of the fan at fixed values
3. Once the measures are taken, repeat the experiment with the spike exchanger.
11.7.2 Observations:
Table 11.3: Temperatures for different geometry of exchangers
11.7.3 Graph
Draw the Graph of temperatures (y-Axis) and AR-1 (X- Axis)
11.7.4 Conclusion
11.8 Specimen Calculation
NIL
11.9 Statistical Analysis
NIL
No
AR-1
(Ohm)
SC-1
(l/s)
ST-1
(°C)
ST-2
(°C)
ST-3
(°C)
ST-4
(°C)
ST-5
(°C)
ST-6
(°C)
ST-7
(°C)
Blade
Heat
exchanger
spike
exchanger
90
11.10 Questions
1) Write is difference on temperatures in free and forced convection. Explain
2) What is free and forced convection
3) What is effect on heat transfer by changing the geometry of exchanger
11.11 Comments
91
12. LAB SESSION 12
To calculate logarithmic mean temperature difference (LMTD), global heat transfer
coefficient and effectiveness of turbulent flow heat exchanger
12.1 Learning Objective
1) Balance the energy in the Turbulent Flow exchanger.
2) Calculate the heat exchanger effectiveness by NTU method.
12.2 Apparatus
Turbulent Flow Heat Exchanger (TIFTC) (Serial no TIFT 0003/06)
12.3 Main Parts
IDENTIFICATION
DESCRIPTION
ST-1
Temperature sensor in the water tank.
ST-2
Cold water temperature sensor at the exchanger inlet or outlet
ST-3
Hot water sensor at the exchanger inlet
ST-4
Cold water sensor between the first and second stretch of the
exchanger
ST-5
Hot water sensor between the first and second stretch of the
exchanger
ST-6
Cold water sensor between the second and third stretch of the
exchanger
ST-7
Hot water sensor between the second and third stretch of the
exchanger
ST-8
Cold water temperature sensor at the exchanger inlet or outlet
ST-9
Hot water sensor at the exchanger outlet
ST-10
Temperature sensor of the exterior surface of the interior tube at
the exchanger
Inlet.
ST-11
Temperature sensor of the exterior surface of the interior tube at
the exchanger
Outlet
SC-1
Hot water flow sensor
SC-2
Cold water flow sensor
AVR-1
Hot water flow regulation valve.
AVR-2
Cold water flow regulation valve
AN-1
Water level switch of the tank
AR-1
Electric resistance
AB-1
Centrifugal pump for hot water circulation
AP-1
Cold water circuit purge
AP-2
Hot water circuit purge
AV-2,AV-3, AV-4
and AV-5
Ball valves of the cold water circuit to fix parallel or crosscurrent
flow
AV-1,AV-6, AV-7
and AV-8
Ball valves to drain the pipes
92
12.4 Useful Data
Exchange Length: L = 3 × 0.5 = 1.5 m.
12.4.1 Interior Tube
Internal Diameter: D
int
= 8×10
- 3
m
External Diameter: D
ext
= 10×10
- 3
m
Thickness = 10
- 3
m
Internal heat transference area: A
h
= 0.0377 m
2
External heat transference area: A
c
= 0.0471 m
2
12.4.2 Exterior Tube
Internal Diameter: D
int,c
=13×10
- 3
m
External Diameter: D
ext,c
=15×10
- 3
m
Thickness = 10- 3 m
12.4.3 Base Unit
Net weight: 30 kg.
Height: 400 mm
Width: 1000 mm
Depth: 500 mm
12.4.4 Heat Exchanger
Net weight: 20 kg.
Height: 200 mm
Width: 1000 mm
Depth: 500 mm
12.4.5 Physical Properties of The Hot And Cold Water
To determine their physical properties, the average temperature of each fluid has to be
calculated.
Hot water average temperature: Tm
h
=
Cold Water Average Temperature: Tm
c
=
From the table of the appendix A, the physical properties based on the average temperature can
be obtained
12.4.6 Mass Flow Rates
The mass flows of both fluids, are going to be obtained from the measurements taken in
the flow sensors (SC1 for hot water and SC2 for cold water)
m (kg/s) = .SC=
Cp=Specific
heat(J/kgK)
= Dynamic
viscosity (kg/ms)
Hot water at Tm
h
°C
h
=
Cp
h
h
Cold water at Tm
c
°C
c
=
Cp
h
c
93
Mass flow for hot water= m
h
(kg/s) = .SC=
Mass flow for cold water= m
c
(kg/s) = .SC=
Figure 12.1: Schematic Diagram of Experiment
12.5 Theory
12.5.1 Heat transference in heat exchangers
A heat exchanger is a device developed by humans for the heat transference between two fluids
at different temperatures separated by a solid wall. They have many engineering applications
and, as a consequence, there are many models adapted to each application. The simplest one is
the one built with two concentric tubes, where fluids can move in the same sense or in the
opposite one. In parallel flow, the hot and the cold water go in and out through the same end.
In crosscurrent flow, the fluids go in and out through opposite ends and they circulate in
opposite senses.
94
12.5.2 Overall Heat-Transfer Coefficient
The overall heat-transfer coefficient U is defined by the relation
q=UA∆T
overall
Equation 12.1 Overall heat transfer coefficient
Although final heat-exchanger designs will be made on the basis of careful calculations of U,
it is helpful to have a tabulation of values of the overall heat-transfer coefficient for various
situations that may be encountered in practice
12.5.3 The Log Mean Temperature Difference (LMTD)
Being ∆T
1
= T
h,i
- T
c,i
and ∆T
2
= T
h,o
- T
c,o
in parallel flow
And
∆T
1
= T
h,i
- T
c,o
and ∆T
2
= T
h,o
- T
c,i
in counter current flow.
T
lm
=
Equation 12.2: The Log Mean Temperature Difference
12.5.4 Effectiveness-Ntu Method
Effectiveness=
Equation 12.3
12.5.5 Capacity coefficient
Capacity coefficient will be defined as (CR)
C
r
=
=……….
Equation 12.4
Mass flow rate multiplied by specific heat) C
h
and C
c
for the hot and cold fluids respectively,
and denoting the smaller one as C
min
95
12.5.6 Reynolds number
Reynolds number (Re) is a dimensionless quantity that is used to help predict similar flow
patterns in different fluid flow situations. The Reynolds number is defined as the ratio of
momentum forces to viscous forces and consequently quantifies the relative importance of
these two types of forces for given flow conditions. They are also used to characterize different
flow regimes within a similar fluid, such as laminar or turbulent flow
1) Laminar flow occurs at low Reynolds numbers, where viscous forces are dominant, and
is characterized by smooth, constant fluid motion;
2) Turbulent flow occurs at high Reynolds numbers and is dominated by inertial forces,
which tend to produce chaotic eddies, vortices and other flow instabilities.
Readers can read further detail from book “heat transfer by J.P Holman” in “chapter 10”
12.6 Objective 01
Balance the energy in the Turbulent Flow exchanger.
12.6.1 Procedure:
1. Check that the valves are opened and that we have crosscurrent flow configuration.
2. Check that the heating tank is full of water, above the level switch
3. Switch on the pump and the resistor (Equipment supply)
4. Fix the tank temperature at 50 °C (STI)
5. Fix the hot water flow in 3 l/min (SCI) and adjust the cold-water flow until reaching
stationary operation conditions maintaining constant the temperature fixed in the tank.
6. Note down the temperature and flow measures in the experimental sheet
7. Repeat steps 5 and 6 for different water temperatures in the deposit 55 °C, 60°C and 65 °C.
8. Once the measures are made, Calculate the heat transferred by the hot water, the heat
absorbed by the cool water, the heat loses, the logarithmic mean temperature and global
heat transference coefficient
96
12.6.2 Observations
Table 12.1: Temperature at different points of turbulent flow heat exchanger
12.6.3 Calculated Data
Table 12.2: Heat transfer calculation in turbulent flow heat exchanger
TEST 1
TEST 2
TEST 3
TEST 4
ST1 (°C)
ST2 (°C)
ST3 (°C)
ST4 (°C)
ST5 (°C)
ST6 (°C)
ST7 (°C)
ST8 (°C)
ST9 (°C)
ST10 (°C)
ST11 (°C)
SC1 (l/min)
3
3
3
3
SC2 (l/min)
TEST 1
TEST 2
TEST 3
TEST 4
q
h (w)
q
c (w)
q
l (w)
∆T
lm
(K)
U (w/m
2
k)
97
12.6.4 Specimen Calculations
12.6.4.1 Heat transferred by the hot water
q
h
=m
h
Cp
h
(Th
i
-Th
o
)=………………..watt
12.6.4.2 Heat absorbed by the cold water
q
c
=m
c
Cp
c
(Tc
o
-Tc
i
)=………………..watt
12.6.4.3 Heat Losses
q
l=
q
h-
q
c
=……………………watt
12.6.4.4 Logarithmic temperatures mean difference between hot water and cold water
Being ∆T
1
= T
h,i
- T
c,i
and ∆T
2
= T
h,o
- T
c,o
in parallel flow
∆T
1
= T
h,i
- T
c,o
and ∆T
2
= T
h,o
- T
c,i
in counter current flow.
T
lm
=
12.6.4.5 Global heat transference coefficient= (U)
From the heat transfer rate Q=UA∆T
lm
U.A=q/∆T
lm
= q
h
/∆T
lm
=……………..w/k
If we take an average heat transfererence area
A
m
=π.L
= π.1.5.
=0.04241m
2
Where
D
int
=8.10
-3
m and D
ext
=10.10
-3
m are interior and exterior diameters of the interior tube and
L=1.5 m is the exchanger length. Finally, global heat transference coefficient will be
12.7 Objective:02
Calculate the heat exchanger effectiveness by NTU method.
12.7.1 Procedure
1. Check that the valves are opened and that we have crosscurrent flow configuration.
2. Check that the heating tank is full of water, above the level switch
3. Switch on the pump and the resistor (feeding of the equipment)
4. Fix the tank temperature at 65 °C (STI)
98
5. Fix the hot water flow in 2.5 l/min (SCI) and adjust the cold-water flow until reaching
stationary operation conditions maintaining constant the temperature fixed in the tank.
6. Note down the temperature and flow measures in the experimental sheet
7. Place conveniently the valves to invert the cold-water flow sense obtaining a parallel flow
8. Make sure that the 65 °C are maintained in the tank and that the same hot and cold-water
flows fixed in step 5 are also maintained.
9. Once the system is stabilized, note down the measures and flows in the experimental sheet.
10. Once the measures are taken, calculate the experimental effectiveness, the theoretical
effectiveness with the NTU method and theoretical temperatures at the exchanger outlet.
12.7.2 Observations
Table 12.3: Temperature for parallel and cross flow
TEST 1
Crosscurrent Flow
TEST 2
Parallel Flow
ST1 (°C)
ST2 (°C)
ST3 (°C)
ST4 (°C)
ST5 (°C)
ST6 (°C)
ST7 (°C)
ST8 (°C)
ST9 (°C)
ST10 (°C)
ST11 (°C)
SC1 (l/min)
SC2 (l/min)
99
12.7.3 Calculations
From these measures, calculate the following thermodynamic variables
Experimental effectiveness (ϵ)
Heat transferred by the hot water (q
h
)
Logarithmic temperatures mean difference between hot and cold water (∆T
lm
)
Parameters: U.A, NTU and C
R
Effectiveness obtained by NTU method (ϵ
NTU
)
Hot and cold water temperatures at the exchanger outlet obtained from the experimental
effectiveness (T
h
,˳y,T
c,o
)
Table 12.4: Effectiveness of turbulent flow exchanger
12.7.4 Specimen Calculations
The effectiveness is the quotient between the heat really exchanged and the maximum heat
that could be transferred in an infinite area exchanger in a crosscurrent flow.
If m
h
Cp
h
˂m
c
Cp
c
ϵ=
m
h
Cp
h
˃m
c
Cp
c
ϵ=
12.7.4.1 Heat transferred by the hot water
q
h
=m
h
Cp
h
(Th
i
-Th
o
)=………………..watt
12.7.4.2 Logarithmic temperatures mean difference between hot water and cold water
Being ∆T
1
= T
h,i
- T
c,i
and ∆T
2
= T
h,o
- T
c,o
in parallel flow
∆T
1
= T
h,i
- T
c,o
and ∆T
2
= T
h,o
- T
c,i
in counter current flow.
TEST 1
Crosscurrent Flow
TEST 2
Parallel flow
ϵ
q
h (w)
∆T
lm
(K)
U.A (w/k)
NTU
C
R
ϵ
NTU
100
T
lm
=
From the heat transfer rate Q=UA∆T
lm
U.A=q/∆T
lm
= q
h
/∆T
lm
=……………..w/k
12.7.4.3 Number of transmission units
Calculating NTU
NTU= ϵ=
12.7.4.4 Capacity coefficient
Capacity coefficient is determined by
C
r
=
=……….
Once the NTU and C
r
are obtained, we can calculate the effectiveness, but depending if the
flow is in crosscurrent or in parallel flow, we will have to use different expressions
=
For Parallel flow
=
For Crosscurrent flow
Comparing the value of ϵ
with ϵ
NTU
we will have to observe if both values are similar or, if
on the other hand, they are very different one from each other
12.8 Graph
Draw the graph between the temperature distribution for parallel and crosscurrent flow. To do
this, place temperature values on the vertical (y-) axis for the hot water, cold water and of the
interior tube surface in ºC (T); and in the x-axis place the position along the exchanger in meters
(x). Take into account that the exchange length is 1.5m and that there are four points to measure
the temperature
12.9 Statistical Analysis
1) x
avg
=
2) S
x
=
12.10 Conclusion
101
12.11 Questions
1) What is the difference between the temperature distribution for parallel and crosscurrent
flow?
2) What is Global heat transference coefficient
3) What is Logarithmic temperatures mean difference
12.12 Comments
102
13. LAB SESSION 13
To calculate logarithmic mean temperature difference (LMTD), global heat transfer coefficient
and effectiveness of shell and tube heat exchanger
13.1 Learning Objective
[i] Balance the energy in the Shell and Tube exchanger
[ii] Calculate the heat exchanger effectiveness by NTU method.
13.2 Apparatus
EDIBON TICT's Shell and Tube exchanger (Serial No= TICT ɸɸ 67/11)
13.3 Main Parts
IDENTIFICATION
DESCRIPTION
ST-16
Water Tank Temperature Sensor
ST-1
Hot Water Temperature sensor at the inlet/outlet of the exchanger
ST-2
Hot Water Temperature Sensor at the outlet of the exchanger
ST-3
Cold Water Temperature Sensor at the inlet/outlet of the exchanger
ST-4
Cold Water Temperature Sensor in the first section of the
exchanger
ST-5
Cold Water Temperature Sensor in the second section of the
exchanger
ST-6
Cold Water Temperature Sensor in the third section of the
exchanger
ST-7
Cold Water Temperature Sensor at the inlet/outlet of the exchanger
SC-1
Hot water flow sensor
SC-2
Cold water flow sensor
AVR-1
Hot water flow regulation valve.
AVR-2
Cold water flow regulation valve
AN-1
Water level switch of the tank
AR-1
Electric resistance
AB-1
Hot Water Flow Centrifugal Pump
AP-1
Cold Water Circuit Purge Valve
AP-2
Hot Water Circuit Purge Valve
AV-2,AV-3, AV-4 Y
AV-5
Ball valves of the cold water circuit to fix parallel or crosscurrent
flow
103
13.4 Useful Data
Exchange Length: L = 0.5 m.
13.4.1 Interior Tube
Internal Diameter: D
int
= 8×10
- 3
m
External Diameter: D
ext
= 10×10
- 3
m
Thickness = 10
- 3
m
Internal heat transference area: A
h
= 0.0126 m
2
External heat transference area: A
c
= 0.0157 m
2
13.4.2 Exterior Tube
Internal Diameter: D
int,c
=0.148 m
External Diameter: D
ext,c
=0.160 m
Thickness =6 ×10
- 3
m
13.4.3 Base Unit
Net weight: 30 kg.
Height: 400 mm
Width: 1000 mm
Depth: 500 mm
13.4.4 Heat Exchanger
Net weight: 20 kg.
Height: 300 mm
Width: 1000 mm
Depth: 500 mm
13.4.5 Physical Properties Of The Hot And Cold Water
To determine their physical properties, the average temperature of each fluid has to be
calculated.
Hot water average temperature: Tm
h
=
Cold Water Average Temperature: Tm
c
=
From the table of the appendix A, the physical properties based on the average temperature can
be obtained
AV-1, AV-6, AV-7 Y
AV-8
Ball valves to drain the pipes
AVS-1
Safety Valve
AVS-2
Safety Valve
Cp=Specific
heat(J/kgK)
= Dynamic
viscosity (kg/ms)
Hot water at Tm
h
°C
h
=
Cp
h
h
Cold water at Tm
c
°C
c
=
Cp
h
c
104
13.4.6 Mass Flow Rates
The mass flows of both fluids, are going to be obtained from the measurements taken in
the flow sensors (SC1 for hot water and SC2 for cold water)
m (kg/s) = .SC=
Mass flow for hot water= m
h
(kg/s) = .SC=
Mass flow for cold water= m
c
(kg/s) = .SC=
Figure 13.1: Schematic Diagram of Experiment
Table 13.1: Valve positions of shell and tube heat exchanger
COUNTERCURRENT FLOW
AV-2 Valve
CLOSED
AV-3 Valve
OPEN
AV-4 Valve
OPEN
AV-5 Valve
CLOSED
PARRALLEL FLOW
AV-2 Valve
OPEN
AV-3 Valve
CLOSED
AV-4 Valve
CLOSED
AV-5 Valve
OPEN
105
13.5 Theory
13.5.1 Heat transference in heat exchangers
A heat exchanger is a device developed by humans for the heat transference between two fluids
at different temperatures separated by a solid wall. They have many engineering applications
and, as a consequence, there are many models adapted to each application. The simplest one is
the one built with two concentric tubes, where fluids can move in the same sense or in the
opposite one. In parallel flow, the hot and the cold water go in and out through the same end.
In crosscurrent flow, the fluids go in and out through opposite ends and they circulate in
opposite senses.
Figure 13.2: Parallel and counter parallel flow
13.5.2 Shell and tube heat exchanger
A shell and tube heat exchanger is a class of heat exchanger designs. It is the most common
type of heat exchanger in oil refineries and other large chemical processes, and is suited for
higher-pressure applications. As its name implies, this type of heat exchanger consists of a shell
(a large pressure vessel) with a bundle of tubes inside it. One fluid runs through the tubes, and
another fluid flows over the tubes (through the shell) to transfer heat between the two fluids.
The set of tubes is called a tube bundle, and may be composed of several types of tubes: plain,
longitudinally finned, etc.
Figure 13.3: Shell and tube heat exchanger
13.5.3 Overall Heat-Transfer Coefficient
The overall heat-transfer coefficient U is defined by the relation
106
q=UA∆T
overall
Overall heat transfer coefficient
Although final heat-exchanger designs will be made on the basis of careful calculations of U,
it is helpful to have a tabulation of values of the overall heat-transfer coefficient for various
situations that may be encountered in practice
13.5.4 The Log Mean Temperature Difference (LMTD)
Being ∆T
1
= T
h,i
- T
c,i
and ∆T
2
= T
h,o
- T
c,o
in parallel flow
∆T
1
= T
h,i
- T
c,o
and ∆T
2
= T
h,o
- T
c,i
in countercurrent flow.
T
lm
=
13.5.5 Effectiveness-Ntu Method
Effectiveness=
13.5.6 Capacity coefficient
Capacity coefficient will be defined as (CR)
C
r
=
=……….
Mass flow rate multiplied by specific heat) C
h
and C
c
for the hot and cold fluids respectively,
and denoting the smaller one as C
min
13.5.7 Reynolds number
In fluid mechanics, the Reynolds number (Re) is a dimensionless quantity that is used to help
predict similar flow patterns in different fluid flow situations. The Reynolds number is defined
as the ratio of momentum forces to viscous forces and consequently quantifies the relative
importance of these two types of forces for given flow conditions. They are also used to
characterize different flow regimes within a similar fluid, such as laminar or turbulent flow
3) Laminar flow occurs at low Reynolds numbers, where viscous forces are dominant,
and is characterized by smooth, constant fluid motion;
4) Turbulent flow occurs at high Reynolds numbers and is dominated by inertial forces,
which tend to produce chaotic eddies, vortices and other flow instabilities.
107
13.6 Objective 1
Balance the energy in the Shell and Tube exchanger
13.6.1 Procedure:
1. Check that the valves are opened and that we have parallel flow configuration.
2. Check that the heating tank is full of water, above the level switch.
5) Switch on the pump and the resistor (equipment supply).
6) Set the tank temperature at 45 ºC (ST16).
7) .Fix the hot water flow in about 3 l/min (SC1) and adjust cold water flow until reaching
stationary operating conditions keeping the temperature set in the tank constant.
8) Write down temperature and flow measurements on the experimental sheet.
9) Repeat steps 5 and 6 for different water temperatures in the tank: 50ºC, 55ºC and 60
ºC.
10) Once the measurements may have been taken, you may calculate the heat transferred
by the hot water, the heat absorbed by the cool water, heat losses, the logarithmic mean
temperature and the global heat transfer coefficient
13.6.2 Observations
Table 13.2: Temperatures at shell and tube heat exchanger
TEST 1
TEST 2
TEST 3
TEST 4
ST
16
45
50
55
60
ST
1
(°C)
ST
2
(°C)
ST
3
(°C)
ST
4
(°C)
ST
5
(°C)
ST
6
(°C)
ST
7
(°C)
SC1 (l/min)
3
3
3
3
SC2 (l/min)
108
13.6.3 Calculated Data
Table13.3: Heat transfer coefficient of shell and tube heat exchanger
13.6.4 Specimen Calculations
13.6.4.1 Heat transferred by hot water (q
h
)
q
h
= m
h
Cp
h
( T
h,i
- T
h,o
)
13.6.4.2 Heat absorbed by the cold water (q
c
)
q
c
= m
c
Cp
c
( T
c,o
- T
c,i
)
Where m
h
and m
c
are the mass expenses, and Cp
h
and Cp
c
are the specific heats of the hot and
cold fluids
Note: Theoretically q
h
should equal q
c
but due to environmental energy losses and to
instrumental and observation measurement errors, they are not always equal
13.6.4.3 Heat losses (q
l
)
q
l=
q
h-
q
c
13.6.4.4 Logarithmic average temperatures difference between hot and cold water
(∆T
lm
)
Being ∆T
1
= T
h,i
- T
c,i
and ∆T
2
= T
h,o
- T
c,o
in parallel flo
∆T
1
= T
h,i
- T
c,o
and ∆T
2
= T
h,o
- T
c,i
in countercurrent flow.
T
lm
=
13.6.4.5 Global heat transfer coefficient (U)
q = U A ∆T
lm
Global Heat Transfer Coefficient multiplied by the Transfer Area will be
U. A=
Note: U can be calculated obtaining an average value of the heat transfer area: A
m
= 0.00192
TEST 1
TEST 2
TEST 3
TEST 4
q
h (w)
q
c (w)
q
l (w)
∆T
lm
(K)
U (w/m
2
k)
109
13.7 Objective 2
Calculate the heat exchanger effectiveness by NTU method.
13.7.1 Procedure
1. Check that the valves are opened and that we have countercurrent flow configuration.
2. Check that the heating tank is filled with water above the level switch.
3. Switch on the pump and the resistor (equipment supply).
4. Set the tank temperature in 60 ºC (ST16).
5. Fix the hot water flow in 3 l/min approx. (SC1) and adjust cold water flow to reach stationary
operating conditions, keeping constant temperatures set for the tank.
6. Write down the temperature and flow measurements on the experimental sheet.
7. Set the valves appropriately in order to invert cold water flow direction to produce a parallel
flow configuration.
8. Make sure that 60ºC temperatures are kept in the tank and that the same hot and cold water
flows set in step 5 are also maintained.
9. Once the system is stabilized, write down the temperature measurements and flow values on
the experimental sheet.
10. Once the measurements have been taken, calculate the experimental effectiveness, the
theoretical effectiveness by the NTU method and the theoretical temperatures at the exchanger
outlet.
13.7.2 Observations
Table 13.4: Temperatures for shell and tube heat exchanger
TEST 1
TEST 2
ST16
45
50
ST1 (°C)
ST2 (°C)
ST3 (°C)
ST4 (°C)
ST5 (°C)
ST6 (°C)
ST7 (°C)
SC1 (l/min)
3
3
SC2 (l/min)
110
13.7.3 Calculated Data
Table 13.5: Effectiveness of shell and tube heat exchanger
13.7.4 Specimen Calculations
13.7.4.1 Experimental effectiveness (ϵ)
The effectiveness is the quotient between the heat really exchanged and the maximum heat
that could be transferred in an infinite area exchanger in a crosscurrent flow.
If m
h
Cp
h
˂m
c
Cp
c
ϵ=
m
h
Cp
h
˃m
c
Cp
c
ϵ=
13.7.4.2 Logarithmic average temperatures difference between hot and cold water
(∆T
lm
)
Being ∆T
1
= T
h,i
- T
c,i
and ∆T
2
= T
h,o
- T
c,o
in parallel flow
∆T
1
= T
h,i
- T
c,o
and ∆T
2
= T
h,o
- T
c,i
in countercurrent flow.
T
lm
=
13.7.4.3 Global heat transfer coefficient (U)
q = U A ∆T
lm
Global Heat Transfer Coefficient multiplied by the Transfer Area will be
U. A=
13.7.4.4 Number of transmission units
NTU=
TEST 1
Crosscurrent Flow
TEST 2
Parallel flow
ϵ
q
h (
w
)
∆T
lm
(K)
U.A (w/k)
NTU
C
R
ϵ
NTU
111
13.7.4.5 Capacity coefficient
Capacity coefficient is determined by
C
r
=
=……….
Once the NTU and C
r
are obtained, we can calculate the effectiveness, but depending if the
flow is in crosscurrent or in parallel flow, we will have to use different expressions
13.7.4.6 Temperatures at the exchanger outlet
=
For Parallel flow
=
For Crosscurrent flow
13.8 Statistical Analysis
For overall heat transfer coefficient “U”
1) x
avg
=
2) S
x
=
13.9 Conclusion
13.10 Questions
1) What is the difference between the temperature distribution for parallel and crosscurrent
flow in shell and tube heat exchanger
2) What is Global heat transference coefficient
3) What is Logarithmic temperatures mean difference
4) What is difference of shell and tube heat exchanger from other heat exchangers
13.11 Comments
112
14. LAB SESSION 14
To calculate logarithmic mean temperature difference (LMTD) and global heat transfer
coefficient of plate heat exchanger
14.1 Learning Objective
Balance the energy in the Shell and Tube exchanger
14.2 Apparatus
EDIBON’s TIPL Plate Heat Exchanger (Serial No= TIPL 0047/11)
14.3 Main Parts
14.4 Useful Data
14.4.1 BASE UNIT
Net weight: 30 kg.
Height: 400 mm
Width: 1000 mm
Depth: 500 mm
14.4.2 Heat Exchanger
Net weight: 20 kg.
Height: 300 mm
Width: 1000 mm
Depth: 500 mm
Maximum Flow 12m
3
/h
Max. Work Pressure 10bar
Max. Work Temperature 100ºC
IDENTIFICATION
DESCRIPTION
ST-16
Water Tank Temperature Sensor
ST-1
Cold Water Temperature Sensor at the inlet/Outlet of the
exchanger
ST-2
Hot Water Temperature sensor at the inlet of the exchanger
ST-3
Cold Water Temperature sensor at the inlet/outlet of the exchanger
ST-4
Hot Water Temperature sensor at the outlet of the exchanger
SC-1
Hot water flow sensor
SC-2
Cold water flow sensor
AVR-1
Hot water flow regulation valve.
AVR-2
Cold water flow regulation valve
AN-1
Water level switch of the tank
AR-1
Electric resistance
AB-1
Hot Water Flow Centrifugal Pump
AV-2,AV-3, AV-4 Y
AV-5
Ball valves of the cold water circuit for setting parallel or counter
current flow
AV-1,AV-6, AV-
7 and AV-8
Ball valves for draining the pipes
113
Minimum. Work Temperature 0ºC
Maximum number of plates 10
Internal Circuit Capacity 0.176 liters
External Circuit Capacity 0.22 liters
Surface 0.32m
2
Pressures drop 1.4 m.c.a.
14.4.3 Physical Properties of The Hot and Cold Water
To determine their physical properties, the average temperature of each fluid has to be
calculated.
Hot water average temperature: Tm
h
=
Cold Water Average Temperature: Tm
c
=
From the table of the appendix A, the physical properties based on the average temperature can
be obtained
14.4.4 Mass Flow Rates
The mass flows of both fluids, are going to be obtained from the measurements taken in
the flow sensors (SC1 for hot water and SC2 for cold water)
m (kg/s) = .SC=
Mass flow for hot water= m
h
(kg/s) = .SC=
Mass flow for cold water= m
c
(kg/s) = .SC=
Cp=Specific
heat(J/kgK)
= Dynamic
viscosity (kg/ms)
Hot water at Tm
h
°C
h
=
Cp
h
h
Cold water at Tm
c
°C
c
=
Cp
h
c
114
Figure 14.1: Schematic Diagram of Experiment
Table 14.1: Position of valves in plate heat exchanger
COUNTERCURRENT FLOW
AV-2 Valve
CLOSED
AV-3 Valve
OPEN
AV-4 Valve
OPEN
AV-5 Valve
CLOSED
PARRALLEL FLOW
AV-2 Valve
OPEN
AV-3 Valve
CLOSED
AV-4 Valve
CLOSED
AV-5 Valve
OPEN
115
14.5 Theory
14.5.1 Heat transference in heat exchangers
A heat exchanger is a device developed by humans for the heat transference between two fluids
at different temperatures separated by a solid wall. They have many engineering applications
and, as a consequence, there are many models adapted to each application. The simplest one is
the one built with two concentric tubes, where fluids can move in the same sense or in the
opposite one. In parallel flow, the hot and the cold water go in and out through the same end.
In crosscurrent flow, the fluids go in and out through opposite ends and they circulate in
opposite senses.
Figure 14.2: Parallel and counter parallel flow
14.5.2 Plate heat exchanger
Plate heat exchanger is a type of heat exchanger that uses metal plates to transfer heat between
two fluids. This has a major advantage over a conventional heat exchanger in that the fluids
are exposed to a much larger surface area because the fluids spread out over the plates. This
facilitates the transfer of heat, and greatly increases the speed of the temperature change. Plate
heat exchangers are now common and very small brazed versions are used in the hot-water
sections of millions of combination boilers. The high heat transfer efficiency for such a small
physical size has increased the domestic hot water (DHW) flow rate of combination boilers.
The small plate heat exchanger has made a great impact in domestic heating and hot-water.
Larger commercial versions use gaskets between the plates, whereas smaller versions tend to
be brazed.
14.5.3 Overall Heat-Transfer Coefficient
The overall heat-transfer coefficient U is defined by the relation
q=UA∆T
overall
Overall heat transfer coefficient
Although final heat-exchanger designs will be made on the basis of careful calculations of U,
it is helpful to have a tabulation of values of the overall heat-transfer coefficient for various
situations that may be encountered in practice
14.5.4 The Log Mean Temperature Difference (LMTD)
Being ∆T
1
= T
h,i
- T
c,i
and ∆T
2
= T
h,o
- T
c,o
in parallel flow
∆T
1
= T
h,i
- T
c,o
and ∆T
2
= T
h,o
- T
c,i
in countercurrent flow.
116
T
lm
=
The Log Mean Temperature Difference
14.6 Objective
Balance the energy in the Shell and Tube exchanger
14.6.1 Procedure
1. Verify that valves are opened and that parallel flow configuration has been set.
2. Verify that the heating tank is filled with water over the level switch.
3. Turn on the pump and the resistance (the equipment power supply).
4. Set the tank temperature in 50ºC (ST16).
5. Set the hot water flow in 3 l/min approx. (SC1) and adjust the cold water flow so stationary
operating conditions may be reached keeping the temperature in the tank constant
6. Write down temperature and flow measurements on the experimental sheet.
7. Repeat steps 5 and 6 for different temperatures of the water tank: 55ºC, 60ºC and 65ºC.
8. Once the measurements have been taken you may calculate the heat transferred by the hot
water, the heat absorbed by the cold water, heat losses, the logarithmic average temperatures
difference and the heat transfer global coefficient
14.6.2 Observations
Table 14.2: Temperatures of Plate Heat Exchangers
TEST 1
TEST 2
TEST 3
TEST 4
ST16
50
55
60
65
ST1 (°C)
ST2 (°C)
ST3 (°C)
ST4 (°C)
SC1 (l/min)
3
3
3
3
SC2 (l/min)
117
14.6.3 Calculated Data
Table14.3: Heat transfer in Plate heat exchanger
14.6.4 Specimen Calculations
14.6.4.1 Heat transferred by hot water (q
h
)
q
h
= m
h
Cp
h
( T
h,i
- T
h,o
)
14.6.4.2 Heat absorbed by the cold water (q
c
)
q
c
= m
c
Cp
c
( T
c,o
- T
c,i
)
Where m
h
and m
c
are the mass expenses, and Cp
h
and Cp
c
are the specific heats of the hot and
cold fluids
Note: Theoretically q
h
should equal q
c
but due to environmental energy losses and to
instrumental and observation measurement errors, they are not always equal
14.6.4.3 Heat losses (q
l
)
q
l=
q
h-
q
c
14.6.4.4 Logarithmic average temperatures difference between hot and cold water
(∆T
lm
)
Being ∆T
1
= T
h,i
- T
c,i
and ∆T
2
= T
h,o
- T
c,o
in parallel flow
∆T
1
= T
h,i
- T
c,o
and ∆T
2
= T
h,o
- T
c,i
in countercurrent flow.
T
lm
=
14.6.4.5 Global heat transfer coefficient (U)
q = U A DT
lm
Global Heat Transfer Coefficient multiplied by the Transfer Area will be
U. A=
TEST 1
TEST 2
TEST 3
TEST 4
q
h (w)
q
c (w)
q
l (w)
∆T
lm
(K)
U (w/m
2
k)
118
Note: U can be calculated obtaining an average value of the heat transfer area: A
m
= 0.192
14.7 Graph
Represent the temperature distribution in counter-current and parallel flow configurations. For
that purpose, represent hot and cold water temperature values in ºC (T) on the vertical axis; and
the position along the exchanger in meters on the horizontal axis. You should consider the
length of the exchanger to be 0.5m and that we have three measure points.
14.8 Statistical Analysis
For overall heat transfer coefficient “U”
1) x
avg
=
2) S
x
=
14.9 Conclusion
14.10 Questions
1) What is the difference between the temperature distribution for parallel and crosscurrent
flow in Plate heat exchanger
2) What is Global heat transference coefficient
3) What is Logarithmic temperatures mean difference
4) What is difference of Plate heat exchanger from other heat exchangers
14.11 Comments
119
120
