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Transcript of Sample Copy. Not For Distirbution.x REFRIGRATION AND AIR-CONDITIONING S.No Experiments 1. To study...
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Engineering Practical Book-Vol-1
Thermal
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iii
ENGINEERING
PRACTICAL BOOK Vol-1
THERMAL
By
Dr Farrukh Hafeez &
Mohd Arif
EDUCREATION PUBLISHING (Since 2011)
www.educreation.in
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iv
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v
PREFACE
The importance of practical training in engineering education, as emphasized by the
AICTE, has motivated the authors to compile the work of various engineering
laboratories into a systematic Practical laboratory book. The manual is written in a
simple language and lucid style. It is hoped that students will understand the manual
without any difficulty and perform the experiments.
The manual incorporates latest experiment used to demonstrate the basic principles of
Refrigeration, Air-conditioning (RAC), Heat and Mass Transfer(HMT). Different
components of each experimental rig have been described in detail. Brief theory and
basic fundamentals have been incorporated to understand the experiments and for the
preparation of lab report independently. Sample calculations have been provided to help
the students in tabulating the experimental and theoretical results, comparing and
interpreting them within technical frame. The book also covers the general aspects for the
preparation of a technical report and precautions to be taken in the laboratories for
accurate and save performance of experiments . In end of each experiment questions
related to each experiment have been provided to test the depth of knowledge gained by
students.
The manual has been prepared as per the general requirements of an RAC and HMT
laboratories in any graduate and Diploma level classes syllabus .Refrigeration Air-
Conditioning and Heat Mass Transfer is an important area and its knowledge is applied
in almost all industries. We hope that manual would be useful for establishing a new
laboratory and for the students of all branches. Any suggestions for further improvement
of the manual will be welcome and incorporated in the next edition.
Farrukh Hafeez
Mohd Arif
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ABOUT THE AUTHOR
Dr Farrukh Hafeez is PhD from Jamia Millia Islamia. He has been in teaching
profession for the last 17 years and has experience of serving some of the prestigious
institutions of India and abroad. In the 17 years he has taught graduate and post graduate
courses of mechanical engineering in universities of India such as; Aligarh Muslim
University (a central Government University), Institute of Technology and Management
Gurgaon, IIT Delhi, Jamia Millia Islamia New Delhi , International University of Shaqra
in Saudi . Presently he is serving as an Associate Professor in Aligarh Muslim University.
His experience in writing this book will be helpful for engineering graduate classes and
for establishing thermal Engineering laboratories.
Mohd Arif is M.Tech in thermal Engineering and has an industrial experience of about
20 years in handling latest refrigeration and air-conditioning equipments within and
outside India. For the last ten years he is working as an Assistant Professor in Aligarh
Muslim University and has been engage in various teaching and practical laboratories of
thermal engineering.
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viii
HEAT AND MASS TRANSFER
S.No Experiments
1 To determine the convective heat transfer coefficient in vertical
cylinder and
surrounding air experimentally and empirically. Also to plot the
temperature profile along the length of the cylinder for one set of
readings.
2
To determine the temperature profile along the axis of a given circular
fin experimentally and theoretically f under free convection and to
compare the two profiles. Also determine the efficiency of the fin.
3 (i)To study the construction of a parallel flow heat exchanger
(ii) To find overall heat transfer coefficient as a function of mass flow
rate of water and to measure the effectiveness of the heat exchanger
4
To determine the coefficient of thermal conductivity of a given
asbestos sheet by Guarded hot plate method at different temperatures
and to draw a plot between conductivity and temperature.
5
To determine the temperature profile along the axis of a given circular
fin ( pin fin) experimentally and empirically under forced convection
and to compare the experimental and theoretical values . Also
determine the efficiency of the fin.
6 To determine the emissivity of a test plate surface and plot a graph
between temperature and emissivity.
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ix
7 (i) To study the construction of a counter flow heat exchanger
(ii) To find overall heat transfer coefficient as a function of mass flow
rate of water and To measure the effectiveness of heat exchanger
8
To determine the convective heat transfer coefficient between hot air
and inner surface of a tube in forced convection and compare these
experimental values of convective heat transfer coefficient with the
predicted values.
9
To determine the value of Stefan Boltzmann Constant, used in
radiation heat transfer. Draw a graph also between temperature of disc
and time.
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x
REFRIGRATION AND AIR-CONDITIONING
S.No Experiments
1. To study the cut-sectional model of reciprocating refrigerant
compressor.
2
(i) To study the vapor compression refrigerating system and to
draw
temperature -enthalpy (T-S) and pressure-enthalpy (P-H)
diagrams for the cycle.
(ii) Find power consumed in running the unit from energy meter
readings and finding the disc revolutions of the energy meter.
(ii) Calculate multiplying factor.
3. To find Carnot COP, theoretical COP and actual COP of a vapor
compression refrigeration system and efficiency of the cycle.
4. To study a room conditioner. Also draw flow sheet diagrams of the
unit, air circuit and refrigerant circuit
5. To study and label the air-conditioning test rig.
To determine its coefficient of performance COP
i) Theoretically ii) By rotameter readings
iii From mass flow rate of air actually cooled.
6.
(i) To study the psychometric process, heating, cooling,
humidification,
dehumidification and plot them on a psychometric chart
(ii)To determine sensible heat factor of air in winter air conditioning.
7. To study the ice plant and its working cycle and
2. To determine coefficient of performance (COP) and capacity of the
ice plant.
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xi
8. To study the mechanical heat pump and to compute its actual
coefficient of performance, COP.
9.
Study the effect of sub-cooling and superheating in a vapor
compression refrigeration cycle system
10. Introduction to Cryogenics system by visiting Cryogenics lab
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xii
PROPERTY TABLES AND CHARTS (SI UNITS)
TABLE A–1 Molar mass, gas constant, and ideal-gas specific heats of
some substances
TABLE A–2 Boiling and freezing point properties
TABLE A–3 Properties of solid metals
TABLE A–4 Properties of solid nonmetals
TABLE A–5 Properties of building materials
TABLE A–6 Properties of insulating materials
TABLE A–7 Properties of saturated water
TABLE A–8 Properties of saturated water
TABLE A–9 Properties of saturated ammonia
TABLE A–10 Properties of liquid metals
TABLE A–11 Properties of air at 1 atm pressure
TABLE A–12 Properties of gases at 1 atm pressure
TABLE A–13 Properties of gases at 1 atm pressure
TABLE A–14 Emissivity of surfaces
FIGURE A–15 Solar radiactive properties of materials
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xiii
GENERAL INSTRUCTIONS
To make laboratory experiments safe and effective, each student is expected to follow the
given instructions.
SAFETY INSTRUCTIONS
1. High voltage source in the laboratory should be handled properly under the guidance
of lab assistant, as it may cause a serious accident.
2. All students shall wear aprons /avoid loose clothes, shirts should be properly tucked,
skirts with extra flares should be avoided, slippers are not allowed, shoes with rubber
soles are recommended for mechanical work laboratories.
3. There should be no over-crowding and only trained person should operate the
machine
4. Make sure that all power sources are off during set-up of machines.
5. Keep safe distance from moving parts of machines.
6. Follow the instruction given by the instructor
7. In case of operating furnace, don’t touch the inside parts of furnace.
8. Failure to obey instructions may result in being expelled from the lab
9. Be careful not to damage any machine or instrument. Care must be taken in handling
all instrument
10. Do not start any machine or operate it without the permission from instructor.
11. Lubrication and water-cooling should be checked before starting an engine.
12. All the valves must be opened and close slowly.
13. The application or removal of the load should be gradual.
14. Any unusual behavior or noise of the machine must be reported immediately reported
to the instructor and investigated
PREPARATION OF LAB REPORT
1. Before coming to the laboratory, each student must read and review appropriate
experiment to be conducted on the subsequent turn.
2. Record your experiment observations and sample calculations carefully.
3. Each student is required to write a neat and clean report for the experiment
conducted.
4. Every student should bring his own set of drawing instruments logbooks, slide rule
etc
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xiv
5. Student should get the necessary apparatus issued against their names before starting
the experiment should carefully inspect the apparatus and returned it well to the lab in
charge after finishing the work
6. Reports are due one week after the completion of the experiment.
7. Each report shall be submitted with all necessary instructions, sample calculations,
graphs, and discussion over data and graph.
8. Observations should be recorded in tabular form and in a proper order
9. Sample calculations should be done on a set of most important data. The calculations
should be complete, leading from observed quantities to final results.
10. Results within the scope of the object should be given, with graphical representation
wherever possible.
11. Sources of error should be reported properly. It provides a limit for admissible
inaccuracy in the results.
12. Discussion over results should be analyzed properly and compared with the
manufacture’s rating.
13. A brief criticism of the test procedure and apparatus used with concrete suggestions,
if any, for improvement should be explained. Any unusual occurrence observed
during the test should be reported.
Discussion should reflect the opinion of the writer. It should not be a collection of
merely the self-evident facts.
Questions give at the end of each experiment have to be answered appropriately
with in the space provided in the manual.
tudents should remain prepare for the viva-voce on any turn.
HOW TO PLOT A GRAPH
1. Before drawing a graph between two observed variables it is necessary to know the nature of
expected theoretical graph.
2. Decide which parameter to be considered on X axis and which one on the Y-axis.( parameter
which is under the control of the student is generally kept over X axis)
3. Selection of appropriate scales for the two variables should be chosen such that it appears as
square graph.
4. The following procedure should be observed in drawing the graphs.
(i) A curve should first be drawn freehand in pencil. It should then be faired,
preferably in black ink, with proper instruments.
(ii) Unless otherwise specified, the independent variables should be plotted on the
abscissa.
(iii) The axes should be well defined and bold.
(iv) The scales should be chosen for easy reading with due regard to the accuracy
of the observed quantities so that variations are neither concealed nor
exaggerated. Too large a scale should not be chosen simply to fill a curve
sheet. Some times the scale of abscissa may be taken larger than ordinate to
make the curves clear.
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xv
(v) The scale for the axes may or may not start from zero; but scale for the curves
of efficiency, economy rate, capacity, etc should always start from zero.
(vi) When several curve are drawn over the same abscissa, care must be taken in
choosing the ordinates of the scales such that the curves do not overlap
confusingly.
5. Different indent points should identify each curve separately.
Points plotted should be joined such that it appears smooth and near to the theoretical
nature of the curve. It is not necessary to join all points on the graph. Average graph
is always advisable, instead of point to point plotting. Students shall be encouraged to
use professional software’s for plotting the curves.
GRADING POLICY:
1. The following is the grading policy shall be adopted for the lab report ;
GRADES.
A+
= 10.0
A = 9.5
A
= 9.0
B+
= 8.5
B = 8.0 B
= 7.5
C+
= 7.5
C = 7.0
C
= 6.5
2. Make up Lab: Make up lab is only allowed in the case of valid excuse
3. The distribution is as follows.
Lab reports: 80%
Lab quiz: 10%
Attendance: 10%
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xvi
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HEAT AND MASS TRANSFER
Laboratory-I
Faculty of Engineering and Technology
Aligarh Muslim University
Aligarh
NAME -------------------------------------------------------------------
ROLL NO.---------------------------------------------------------------
BRANCH----------------------------------------------------------------
BATCH-------------------------------------------------------------------
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Engineering Practical Book -Vol-1 - Thermal
1
Experiment No 1 ______________________________________________________
Object
To determine the convective heat transfer coefficient between vertical cylinder and
surrounding air experimentally and theoretically. Plot the temperature profile along
the length of the cylinder for one set of readings.
Apparatus
Free convection apparatus, scale, thermometer.
Theory
When a hot body is kept in still air, heat is transferred by free convection from the outer
surface of the cylindrical tube to the surrounding ambient air contained in a rectangular
enclosure. Heat transfer is given by the expression:
Where
h = convective heat transfer coefficient, W/m2K
A = surface area of cylindrical tube, m2
ts = mean surface temperature of the cylindrical tube, K
t∞ = temperature of the surrounding air, K
For a vertical cylinder in free convection, relations among Nusselt No.,
Grashof No. and Prandtl No. are given by :
Nu = 0.59 ( Gr Pr )1/4
if Gr Pr ≤ 109
Nu = 0.13 ( Gr Pr )1/4
if Gr Pr > 109
Where
Nu = Nusselt number = h L / K
)( ttAhQ s
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Heat And Mass Transfer
2
Pr= gβLD3t n , dimensionless
Pr = Prandtl No. , μ Cp / K , dimensionless
L = Height of the cylinder, m
g = Acceleration due to gravity m2/s
β = Coefficient of thermal expansion for air, 1/T any ideal gas, 1/K
∆t = Difference between mean surface temperature and surrounding air,
K
ν = Kinematic viscosity, m2/s
μ = Coefficient of dynamic viscosity N s / m2
Cp = Specific heat at constant pressure, KJ/Kg K
All properties of air K, Cp, ν , Pr and μ are read at film temperature , tf, from the air
property chart.
2
ttt
sm
f
tsm = Mean surface temperature
t∞ = Ambient temperature of air.
Description of Apparatus
The apparatus consists of a cylindrical tube
enclosed in a rectangular duct open at the top and the
bottom as shown in Fig. 1.
An electrical heating source is embedded in
the cylindrical tube as the heating source. The surface vertical tube
temperature of the tube is measured at different heights
by using thermocouples. The readings of ammeter and air
voltmeter enable us to determine the power dissipated
by the heater and hence the power input to the
cylindrical tube.
Fig. 1 Free Convection Rig
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Engineering Practical Book -Vol-1 - Thermal
3
Procedure
Switch on the mains. Keep the thermocouple selector switch at zero position. Allow the
unit to warm up. Rotate the dimmer knob clockwise and set the power input to any lower
value by looking at the voltmeter and the ammeter. Allow unit to attain steady state.
Ensure that thermocouple readings at positions 1 to 7 do not change with time. Voltmeter
and ammeter readings should be kept constant by rotating and adjusting dimmer knob
slightly for a desired input power. Note down the temperatures as indicated by the
temperature indicator for 1 to 7 positions and ambient temperature. Repeat the
experiment for other input of power to the heating element. About four sets of readings
should be recorded and tabulated as shown in next article.
Observations
S
NO.
V I Q =
V I
in W
Surface Temperature, 0C
Surroundin
g
Temp.0C
t∞
hex
hpre
t1 T2 t3 t4 t5 t6 t7
1 30 0.40 12 31.4 41.
2
51.2 69.
4
77.5 66.2 56.8 17.9
2
3
4
5
Calculations
For one set of readings as shown in the observation table, specimen calculations are as
under mentioned .
Diameter of cylinder, d = 4.5 cm = 0.45 m
Height of the cylinder , L = 50.7 cm = .507m
1. Experimental Value of Convective Heat Transfer Coefficient, hexp.
Q = V I = 30 x .4 = 12 W
7
7654321 tttttttt sm
7
8.562.665.774.697.512.412.31
smt = 56.2 0C
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Heat And Mass Transfer
4
As discussed in theory
Q = h A (tsm - t∞)
12 = h x .0176 x ( 56.2 - 17.9 )
KmWh 2
exp /033.53.380716.
12
2. Predicted Value of Convective Heat Transfer coefficient
Ctt
t sm
f
005.372
9.172.52
2
Tf = 37.05 + 273 = 310.05 K
β = 1 / Tf = 1 / 310.05 = 3.225 x 10-3
/ K
At tf = 37.05 0C , from the enclosed table of properties of air as given in Fig.2.
ν = 16.71 x 10-6
m2/s , Pr = .7108 & K = 0.027 W/mK
So 2
3
tLgGr
26
33
)1071.16(
3.38507.10225.381.9
Gr = 5.635 x 108
Gr Pr = 5.635 x 108 x .7108 = 4.019 x 10
8
So Gr Pr ≤ 109 , so
Nu = 0.59 ( Gr Pr ) ¼
= 0.59 x ( 4.019 x 108 )
1/4
= 83.537
537.83K
Lh
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Engineering Practical Book -Vol-1 - Thermal
5
h = L
K537.83
= 507.0
027.0537.83
hpre. = 4.4487
Results
Compare experimental and predicted values of convective heat transfer coefficient. Find
% deviation between the two values and assign reasons for the deviation.
Precautions
1. Power input to the heating element should be maintained to a constant value by
changing and adjusting the dimmer knob.
2. Steady state should be maintained during the entire period of experimentation. Seven
surface temperatures and ambient temperature should not vary with time.
3. Keep the table neat and clean.
Questions
1. What are the main sources of error?
Ans.
2. Distinguish between free convection and forced convection.
Ans.
3. Is Q = h A ( ts - t∞ ) is a law or statement and why ?
Ans.
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Heat And Mass Transfer
6
4. What is the approximate range of values of convective heat transfer coefficient in free
convection?
Ans.
5. Why is the surface of cylindrical tube polished?
Ans.
6. Why is the cylindrical tube enclosed in a duct?
Ans.
7. Does the movement of air by fan affect the convective heat transfer coefficient?
Ans.
8. Why is the heat transfer by conduction negligible in this experiment?
Ans.
9. Why is the heat transfer by radiation negligible in this experiment?
Ans.
10. What is the value of conductivity of air at room temperature?
Ans.
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Engineering Practical Book -Vol-1 - Thermal
7
Experiment No 2 ______________________________________________________
Objective
To determine the temperature profile along the axis of a given circular fin experimentally
and theoretically f under free convection and to compare the two profiles. Also determine
the efficiency of the fin.
Apparatus
Pin Fin Apparatus as installed in the laboratory.
Theory
Let us consider a pin or fin of circular cross sectional area A as shown in Fig.1 The fin is
attached to a surface whose temperature is to . The fin is transferring heat to the
surrounding fluid at temperature t∞. K is the conductivity of fin material and h convective
heat transfer coefficient between fin periphery and surrounding the air.
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Heat And Mass Transfer
8
Applying energy balance to the differential element, dx we get
Q x = Q x+dx + Qconv.
Which leads to
θ = c1 e-m x
+ c2 e-m x
Where θ = t - t∞
m = Ak
ph where p is the perimeter of the fin.
Putting two boundary conditions:
At x = 0 , θ = θo and
at x = L , KA (d θ / dx )x=L = h A θ x=L
We obtain
mLKmhmL
xLmKmhxLm
sinh)/(cosh
)(sinh)/()(cosh
0
The above equation can be used to predict temperatures anywhere along the length of fin
if convective heat transfer coefficient, h is known.
For the free convection, convective heat transfer coefficient for air can be calculated by
the under mentioned simplified equation.
h = 1.31 (∆ t / d )0.25
∆ t = Temperature difference between fin surface and surrounding air
d = Diameter of the fin
The efficiency η of fin is given by:
η = transferheatpossibleMaximum
transferheatActual=
maxQ
Qa
Qa = AKph LmmKhLm
LmmKhLm
sinh/cosh
cosh/sin
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Engineering Practical Book -Vol-1 - Thermal
9
Qmax = h ( L p ) θo
η = Lm
1
LmmKhLm
LmmKhLm
sinh/cosh
cosh/sin
Description of Apparatus
The apparatus consists of a fin of circular cross-sectional area placed inside an open
duct. One side of the duct is open and other end is connected to the section side of the
blower. Fin is installed near the open end of the duct. The delivery side of the blower is
taken to the atmosphere through a gate valve and an orifice meter. The airflow rate can be
varied by opening the gate valve. The velocity of air can be measured by taking the
difference of two sides of manometer connected to the orifice meter. Mercury is used in
the manometer. A heater is connected to the base of the fin. Five thermocouples are
connected at equal distances along the length and the 6th
thermocouple measures the
temperature of surrounding air.
Specifications
Procedure
Switch on the power. Keep the thermocouple selector switch to zero position. Rotate the
dimmer knob clockwise and set the power input to any desired value by looking at the
voltmeter and the ammeter. Allow the unit to attain steady state. To ensure steady state,
all the six temperatures and input power should not change with time. To maintain
constant input to the unit, rotate and alter the dimmer knob slightly so that voltage and
current do not change with time. Note the readings of voltmeter and ammeter to find the
power input. Turn the thermocouple selector switch clockwise step by step from positions
1 to 6 and note down the six temperatures. Repeat the experiment for other input power
to the heater. At least three sets of readings should be taken.
Diameter of fin, d = 1.2 cm
Length of fin, L = 15 cm
Distance between heater and 1st thermocouple = 1.5 cm
Distance between any two thermocouples = 3.0 cm
Diameter of the orifice = 2.0 cm
Width of the duct = 15 cm
Breadth of the duct = 10 cm
Conductivity of brass = 111 W/mK
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Heat And Mass Transfer
10
Observations
S.NO.
t1
t2
t3
t4
t5
t6
Voltage
in volts
V
Current in
amperes
I
1.
51.6
47.4
43.4
40.5
38.6
16.5
23
0.23
2.
3.
Calculations
One set of observation is shown in the table of observation. Specimen calculations are
shown for these observations.
5
6.385.404.434.476.51 st
= 44.3 0C
∆t = ts - t∞ = 44.3 - 16.5 = 27.8 0C
h = 1.31 (∆t / d )0.25
= 1.31 ( 27.8 / 0.012 )0.25
= 1.31 ( 2308.3 )0.25
= 1.31 x 6.93 = 9.080 W/m2K
AK
phm =
24/ dk
dh
dK
h
4
012.0111
408.9
222.5 /m
h / k m = 9.08 / 111 x 5.222 = 0.015665
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Engineering Practical Book -Vol-1 - Thermal
11
To Predict to
At x = 0.015 m , t = 51.6 0C , t∞ = 16.5
0C
So from 0
mLKmhmL
xLmKmhxLm
sinh/cosh
)(sinh/)(cosh
tt
tt
0
1
mLKmhmL
xLmKmhxLm
sinh/cosh
)(sinh/)(cosh 11
or 5.16
5.166.51
0
t
15.0222.5sinh01566.015.0222.5cosh
)015.015.0(222.5sinh01566.0)015.015.0(222.5cosh
5.16
1.35
0 t
8659.001566.0323.1
76483.001566.02589.1
33656.1
27088.1
9508.0
9508.0
5.169508.1.350
t C042.53
To Calculate t2
At x = 0 .045 m , t = t2 =?
So 5.1642.53
5.162
t
15.0222.5sinh01566.015.0222.5cosh
)045.015.0(22.5sinh01566.0)045.015.0(22.5cosh
33656.1
54831.0sinh01566.054831.0cosh
92.36
5.162
t
33656.1
5762.01566.154.1
33656.1
163.1 = 0 .870
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Heat And Mass Transfer
12
t2 = 48.630CSimilarly t3 , t4 and t5 can be calculated
Now we shall calculate the value of efficiency
mLKmhmL
mLKmhmL
Lm sinh/cosh
cosh/sinh1
7833.0sinh01566.07833.0cosh
7833.0cosh01566.07833.0sinh
15.222.5
1
33650.1
323.101566.08659.0
15.222.5
1
3365.115.022.5
8866.0
= 84.67%
Results
Tabulate the experimental and predicted values of temperatures as shown below :
Temperature,0 C t1 t2 t3 t4 t5
Experimental value 51.6 47.4 43.4 40.5 38.6
Predicted value 48.63
1st set 2
nd set 3
rd set
Value of efficiency 84.67
Plot a graph depicting experimental and predicted values of temperature along the length
of the fin.
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Engineering Practical Book -Vol-1 - Thermal
13
Precautions
1. To obtain correct results, steady state must be maintained.
2. For given power,all the six temperatures must be kept constant with time.
3. For the particular set, power input should not vary with time. The input power should
be maintained constant by rotating and adjusting dimmer knob slightly so that
readings of voltage and ammeter do not change with time.
4. Temperatures as indicated by thermocouples should be calibrated
Questions
1. What are the sources of error?
Ans.
2. What do you understand by the efficiency of a fin?
Ans.
3. What do you understand by fin effectiveness?
Ans.
4. How the concept of effectiveness can be used in industries?
Ans.
5. Does fin always increase rate of heat dissipation to the surroundings?
Ans.
6. State conditions when fin increases heat transfer to the surroundings.
Ans.
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Heat And Mass Transfer
14
7. What type of fins are used in aircrafts and why?
Ans.
8. Why fins are used sometime in forced convection?
Ans.
9. Which type of fins are used for most economical benefit?
Ans.
10. Where annular fins are used?
Ans.
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Engineering Practical Book -Vol-1 - Thermal
15
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