Sample Copy. Not For Distirbution.x REFRIGRATION AND AIR-CONDITIONING S.No Experiments 1. To study...

Sample Copy. Not For Distirbution.

i

Engineering Practical Book-Vol-1

Thermal


ii

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Printed in India


iii

ENGINEERING

PRACTICAL BOOK Vol-1

THERMAL

By

Dr Farrukh Hafeez &

Mohd Arif

EDUCREATION PUBLISHING (Since 2011)

www.educreation.in


iv


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


vi


vii

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.


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.


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.


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.


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


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


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


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.


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%


xvi


HEAT AND MASS TRANSFER

Laboratory-I

Faculty of Engineering and Technology

Aligarh Muslim University

Aligarh

NAME -------------------------------------------------------------------

ROLL NO.---------------------------------------------------------------

BRANCH----------------------------------------------------------------

BATCH-------------------------------------------------------------------


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


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



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



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



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.



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.



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.



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



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



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



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



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.



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.



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.



15

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