Reg. No_________________

Roll. No____________

VINAYAKA MISSIONS UNIVERSITY

SALEM

HEAT TRANSFER LAB

(Final Year B.E./B.Tech. Students)

LAB MANUAL

VINAYAKA MISSIONS KIRUPANANDA VARIYAR

ENGINEERING COLLEGE,

VINAYAKA MISSIONS UNIVERSITY,

SALEM-636 308.

(For Private Circulation only)

2

VINAYAKA MISSIONS UNIVERSITY

V.M.K.V. ENGINEERING COLLEGE

SALEM-636 308

DEPARTMENT OF MECHANICAL ENGINEERING

NAME :

Roll No. :

REG. No. :

YEAR & SEMESTER :

SECTION :

LAB MANUAL

HEAT TRANSFER LAB

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(For Private Circulation Only)

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CONTENTS

EX.No.

DATE EXERCISEPAGE

No.STAFF SIGN.

6

7

HEAT TRANSFER LAB

LIST OF EXPERIMENTS

1. Thermal conductivity by guarded hot plate method

2. Heat exchanger test – parallel and counter flow

3. Heat exchanger test – shell and tube heat exchanger

4. Emissivity measurement

5. COP of a refrigerator

6. Heat transfer from fins-natural and forced convection

7. Thermal conductivity of insulating material

8. Heat transfer through composite walls

9. Heat transfer by free and forced convection

10. Stefan – Boltzman apparatus

11. Boiler trial

8

Tabulation

Sl.

No.

Inner Heater Outer HeaterCooling

PlateThermal

Conductivity

W/mkV

Volts

I

Amp

T1

°C

T2

°C

V2

Volts

I2

Amp

T3

°C

T4

°C

T5

°C

T6

°C

Formula

Thermal Conductivity

Where

W1 = Input to the inner heater in watts = V I

L = Specimen thickness in metre

A = Area = in m2

D = Diameter of the heater plate in metre

X = Width of gap between the heater plates in metre

C =

9

Ex. No: 1 Date:

THERMAL CONDUCTIVITY BY TWO SLAB GUARDED HOT

PLATE METHOD

Aim

To determine the thermal conductivity of the given specimen by using guarded hot

plate method.

Apparatus Required

Thermal conductivity apparatus

Central heater

Guarded heated ring

Description

The heater plate is surrounded by a heating ring for stabilizing the temperature of

the primary heater and prevents heat loss completely around its edges. The primary and

guard heater are made up of mica sheets in which is wound closely with equal space

nichrome wire and packed with upper and lower mica sheets. These heaters together form

a flat which together with upper and lower copper plates and rings form the heater plate

assembly. Two thermo couples are used to measure the hot face temperature at the upper

and lower central heater assembly copper plates two thermocouples are used to check the

balance in both the heater inputs.

Specimens are held between the heater and cooling unit on each side of the

apparatus. Measure the temperature of the upper cooling plate and lower cooling plate

respectively. The heater plate assembly together with the with cooling plates and specimen

held in position by 3 vertical studs and nuts on a base plate are shown in the assembly

drawing. The cooling chamber is a composite assembly of grooced aluminum casting and

aluminum cover with entry and exit adaptors for water inlet and outlet.

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Procedure

The specimen is placed on either side of the heating plate assembly, uniformly

touching the cooling plates. Then the outer container is filled with lose fill insulation such

as glass wool (supplied in small cloth packets). The cooling circuit is opened then

calculated input is given to central and guard heaters through separate single phase supply

lines with a dimmer, stat in each line and it is adjusted to maintain the desired temperature.

The guard heater input is adjusted in such away that there is no radial heat flow which is

checked form thermocouple reading and is adjusted accordingly. The input to the central

heater and the thermocouple readings are reordered in every 10 minutes till a reasonably

steady state condition is reached.

Result:

Thus the thermal conductivity of the specimen is determined.

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Tabulation

Type of

flow

Hot Water Cold Water

LMTD °C

Heat transfer

co-efficient kJ/hr m2

k

Effectiveness (e)

Time taken for 1 liter

water flow in

sec.

Inlet temp T3°C

Outlet

temp T4°C

Time taken for 1 liter

water flow

in sec.

Inlet temp T1°C

Outlet temp T2°C

13

Ex. No: 2 Date:

PARALLEL AND COUNTER FLOW HEAT EXCHANGER

Aim

To study and compare the temperature distribution, heat transfer rate and overall

heat transfer coefficient in parallel and counter flow heat exchanger. To calculate the

effectiveness of parallel flow and counter flow heat exchanger.

Apparatus Required

Stop watch

Measuring tape

Thermometers (0-100) °C

Description

The apparatus consist of concentric tube that exchanger. The hot fluid (i.e. hot

water) is obtained form an electric geyser and it flows through the inner tube. The cold

fluid is cold water and can be admitted at any one of the ends enabling the heat exchanger

to run as a parallel flow apparatus or a counter flow apparatus. This can be done by

operating the different values provided. Temperatures of the fluids can be measured using

thermometers. Flow rate can be measured using stop watch and measuring flask. The out

tube is provided with adequate asbestos rope insulation to minimize the heat loss to the

surroundings.

Procedure

Parallel flow

1. Parallel flow means the direction of cold and hot water flow is the same

2. Adjust the valves of pipes and maintain the same desired direction of flow

3. On the heater and slightly open the inlet valves of cold and hot water and

measure the mass flow of cold and hot water at outlet per litre.

4. Take inlet and outlet temperature of cold and hot water

5. Increase the valve opening and measure the above readings in steps of 200

ml/min. to 1 lit/min.

6. The measured values are tabulated and the required results are obtained.

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Formula:

Heat transfer from hot water,

Where,

mh = Mass flow rate of hot water kg/hr

Ch = Specific heat of hot water = 4.187 kJ/kgK

T3 = Inlet temperature of hot water, C

T4 = Outlet temperature of hot water, C

Heat transfer from cold water

Where, mc = Mass flow rate of cold water kg/hr =

c = Density of cold water

Cc = Specific heat of cold water = 4.187 kJ/kgK

T1 = Inlet temperature of hot water, C

T2 = Outlet temperature of hot water, C

Logarithmic Mean Temperature Difference (LMTD),

= Temperature difference at inlet, C

= Temperature difference at outlet, C

Overall Heat Transfer Coefficient,

Where,

A = Area of the tube in m2

D = Outer diameter of the tube = 12.5mm

L = Length of the tube = 1200mm

Effectiveness,

15

Counter flow1. Counter flow means the direction of cold and hot water is in opposite direction

2. Adjust the valves of pipe and maintain the flow of cold and hot water in the

opposite direction to each other

3. Take the readings of the inlet and outlet temperatures of cold and hot water at

various levels.

4. The measured values are tabulated and the required results are obtained.

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Result

Thus the temperature distribution, heat transfer rate, overall heat transfer co

efficient and effectiveness of the parallel flow and counter flow heat exchangers are

calculated.

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Tabulation

Cold

Water

temp °C

Steam

Inlet

Temp

T3°C

Cond

ensat

e

Quali

ty

T4°C

Condensate

Quality

Heat

Transfer

to water

KJ/hr

Cold Water

flow rate

LMTD

°C

Heat

Transfer

Co-

efficient

KJ/hr

m2°C

Effecti

veness

(E)

Inlet

T1

Out

let

T2

ml tC

Sec

ml/sec Kg/hr

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Ex. No: 3 Date:

SHELL AND TUBE HEAT EXCHANGER

Aim

To determine the overall heat transfer coefficient to determine the heat exchanger

effectiveness.

Apparatus Required

Stop watch

Thermometers (0°C-100°C)

50 ml beaker

Description

In the present setup the unit operates as a condenser with steam condensing over

the tubes and cooling water flowing through the tubes. The design of condensers for such

varied applications as steam power plants, chemical processing plants and nuclear power

plants and for space vehicles involved a variety of heat transfer and fluid flow problems

associated with the condensation of vapours.

The banks of smooth horizontal round tubes configurations and with the high

vapour velocities which are normally associated with steam condenser, the overall heat

transfer co-efficient is primarily a function of cooling water velocity for clean, bright, new

horizontal tubes with no contamination wither on the steam side or on the water side. If the

tubes are of a material other than admiralty metal or have a wall thickness other than

18BWG correction factors indicated in table one should be employed.

The condenser is a horizontal shell and tube heat exchanger with steam condensing

over the tubes. Cooling water flows through tow tube passes. Steam pressure and

temperature at inlet to the exchanger are monitored. The condensate leaves at the bottom

through a valve. The condensate temperature is also monitored. Water inlet and outlet

temperatures are measure by dial thermometers. A manometer is provided for evaluating

the pressure drop in the cooling water circuit. Water flow rate is measured by either

measuring the quantity of water collected in bucket in a known time or by means of rot

meter quantity of steam condensed is measured by collecting the condensate in a

measuring jar.

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Formula

mw = Mass flow rate of water in kg/hr =

Heat transfer to water, in kJ/hr

T1 = Inlet temperature of cold water in C

T2 = Outlet temperature of cold water in C

CPc = Specific heat of cold water = 4.187 kJ/kgK

w = Density of water = 1000 kg/m3

Heat given out by steam =

Where,

L = Latent heat of steam

Qc = Quantity of condensate collected in ml.

tc = Time for collecting condensate in seconds

c = Density of steam at temperature T3 C

Logarithmic Mean Temperature Difference (LMTD) =

Heat transfer =

Where, N = Number of tubes

d0 = Outside diameter of tube in metre

L = Effective length in metre

Overall heat transfer coefficient = kJ/hrm2K

Where, A = Area of tube in m2

D = Outer diameter of tube 12.5mm

L = Length of tube 1200mm

Effectiveness,

Where, T3 = Temperature of steam at inlet, C

T1 = Temperature of water at inlet, C

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Procedure

1. Switch on the boiler heaters

2. In the pump and adjust the mass flow of cold water to 25ml/sec and wait until

the boiler pressure reduces to 0.5kgfcm2.

3. When the boiler pressure is 0.5kgf/cm2

4. Then note the steam inlet temperature and coldwater inlet and outlet temp, and

time taken for 50ml condensate and steam outlet temp.

5. Then varying the mass flow of the cold water to 45, 65,…105 ml/sec.

corresponding readings are tabulated.

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Result

Thus the overall heat transfer co-efficient and effectiveness are determined for the

given shell and tube heat exchanger.

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Tabulation

Sl.No.

Black Plate Test Plate Ambient Temperature°C

Emissivity of test plate

V1

voltsI1

AmpT1

°CV2

voltsI2

AmpT2

°C

25

Ex. No: 4 Date:

EMISSIVITY MEASUREMENT

Aim

To determine the emissivity of the given specimen.

Apparatus Required

Emissivity apparatus

Description

The experimental set up consists of two circular aluminum plates identical in size

and is provided with heating coils sandwiched. The plates are mounted on brackets and are

kept in an enclosure so as to provide undisturbed natural convection surroundings. The

heat input to the heater is varied by separate dimmer stats and is measured by using an

ammeter and a voltmeter with the help of double through switches. The temperature of the

plates is measured by thermocouples. Separate wires are connected to diametrically

opposite points to get the average surface temperature of plates. Another thermocouple is

kept in the enclosure to read the ambient temperature of enclosure. Plate 1 is blackened by

a thick layer of lamp black to form the idealized black surface where as the plate whose

emissivity is to be determined.

The heater inputs to the two plates are dissipated from the plates by conduction,

convection and radiation. The experimental set up is designed in such a way that under

steady state conditions the heat dissipation by conduction and convection is same for both

plates, when the surface temperatures are same and the difference in the heater input

readings is because of the difference in radiation characteristics due to their different

emissivity’s.

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Formula

Where,

W1 = Heater input to black plate = V1I1 Watts

W2 = Heater input to test plate = V2I2 Watts

A = Area of two plates = m2

Diameter of the black and test plate (d) = 160mm

Ts = Surface temperature of discs = T1 + 273K (or) T2 + 273K

T3 = Temperature of enclosure = T3 + 273K

Eb = Emissivity of black plate = 1

= Stefan Boltzmann constant = 5.67 10-8 W/m2K4

By using Stefan Boltzmann Law:

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Procedure

1. Give power supply to T.P. (230 v signal phase) and adjust the reading in it

equal to room temperature by roating the compensation knob (normally this is

pre-adjusted).

2. Select the proper range of voltage on voltmeter

3. Gradually increase the input to the heater to black plate and adjust it to some

value viz., 0,50,75 watts. And adjust the heater input to test plate slightly less

than the black plate 27, 35, 55 watts etc.,

4. Check the temperatures of the two plates with small time intervals and adjust

the input of test plate only, by the dimmer stat so that the two plates will be

maintained at the same temperature.

5. This will require some trial and error and one has to wait sufficiently (more

than one hour or so) to obtain the study state condition.

6. After attaining the steady state condition record the temperatures, and

voltmeter and ammeter readings for both the plates.

7. The same procedure is repeated for various surface temperatures in increasing

order.

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Graph:

Graph is drawn between Surface temperature (X axis) Vs Emissivity (Y axis)

Result

Thus the emissivity of the given specimen is calculated and corresponding graph

has been drawn.

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Em

issi

vity

Surface Temperature in Kelvin

Tabulation

Sl.No.

Compressor work time taken for 30 revolution in second t1

Fan work time taken for 10 revolution in seconds t2

Time taken for one lit water flow in seconds t3

Water Temperature °C

Co-efficient of performance (COP)

Inlet

T1

Outlet

T2

T1-T2

Formula

Heat extracted from water Q = mw CPw (T1 - T2) kJ/hr

Where,

kg/hr

T1 = Inlet temperature of water in C

T2 = Outlet temperature of water in C

CPw = Specific heat of water = 4.186kJ/kgK

= Density of water = 1000kg/m3

Coefficient of Performance,

Where, W = W1+W2

W1 = Compressor work,

W2 = Fan work

31

Ex. No: 5 Date:

PERFORMANCE TEST ON A REFRIGERATOR

Aim

To determine the co-efficient of performance of the refrigerator

Apparatus Required

Refrigerator test rig

Thermometer

Measuring jar

Stop watch

Description

The refrigeration is the process of cooling a space less than the surrounding

temperature. The working substance used in the refrigerator is known as refrigerant. The

refrigerant passes through the compressor to increase the pressure. Then it flows to

condenser where it is condensed at constant pressure. The pressurized liquid refrigerant

expands in the expansion valve. Thus the low pressure and low temperature liquid

evaporates in the evaporator by absorbing the latnt heat of evaporation form the space to

be cooled at constant pressure. Now the vapour again passes through the compressor and

the cycle is repeated again.

Procedure

Before starting the unit, ensure that valves are closed. The water is allowed to flow

at constant rate into the container by opening inlet supply tap. The refrigeration can work

with either solenoid valve or thermostat. First the fan is switched on. Then the following

procedure is followed.

The solenoid valve with thermostat expansion is started, the valve s2, s4 and s5 are

closed and solenoid valve switch is put on. The valves s2, s4 and s5 are closed if the

capillary is put off. then the thermostat is rotated in clockwise direction. The thermostat is

inserted in their respective places. The refrigerator is allowed to run for stabilization. The

no of revolutions of the disc in the energy meter of the compressor and fan are noted down

for a known time.

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Result:

Thus the coefficient of performance of the given refrigerator is calculated

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Tabulation

Experiment Power

supply Fin. Temperature °C

Monometer

Reading

Ambient

Temperatu

re °C

Rate of

Heat

Transfer

Q (J/sec)

Effecti

veness

Amp Volt T1 T2 T3 T4 T5 h1 h2

Natural

Convection

Forced

Convection

35

Ex. No: 6 Date:

HEAT TRANSFER THROUGH PINFIN

Aim

To study the temperature distribution along the length of a pinfin in natural and

forced convection and to determine the heat transfer rate from the fin and the fin

effectiveness.

Description

A brass fin of circular cross section is fitted across a long rectangular duct. The

other end of the duct is connected to the suction side of a bowler and the air flows past the

fin perpendicular to its axis. One end of the fin projects outside the duct and is heated by a

heater. Temperature at five points of the fin measured by chromel alumel thermocouples

embedded on the fine. The air flow rat is measured by an orifice meter fitted on the

delivery side of the bowler.

Procedure

Natural convection

1. Start heating the fin by switching on the meter element and adjust the voltage

on dimmer stat, to 50volts by increasing slowly from 0 onwards

2. Note down the thermocouple reading I to 5

3. When steady state condition is reached record the final reading I to 5 and also

record the ambient temperature reading T6

4. Repeat the same experiment with 100 volts and 120 volts.

Forced Convention

1. Start the heating of fin by switching on the heater and adjust dimmer stat

voltage equal to 100 volts.

2. Start the blowe rand adjust the difference of level in the monmieter H=….cm

with the help of value.

3. Note down the thermocouple reading I to 5 at the time interval of 5 minutes

4. When the steady state steady is reached, note the ambined temp reading 6.

5. Repeat the same experiment with different value of 4 volts.

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Formula

Natural Convection

1. T average = C

2. Tmf = mean film temperature =

3. Grash Number Gr =

where g = acceleration due to gravity = 9.81 m/sec2

β = , ΔT = Taverage- T6

T6 = Temperature of direct fluid

= kinematic viscosity m2/sec (From Data book in table for Tmf oC)

d = diameter of the fin 1.27 x 10-2 m

4. Heat transfer coefficient h =

where Nu = Nusselt Number

= 1.10 x (Gr x Pr)1/6 for 10-1 < Gr x Pr < 104

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= 0.53 x (Gr x Pr)1/4 for 104 < Gr x Pr < 109

= 0.13 x (Gr x Pr)1/3 for 109 < Gr x Pr < 1012

Ka = Thermal conductivity of air W/mK ( From Data book in table for Tmf oC)

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5. m = m-1

Where h = Heat transfer coefficient W/m2K

P = Circumference of the fin = d in metre

K = Thermal conductivity of the material (given specimen), W/mK

kbrass = 110.5 W/mK,

ksteel = 46.5 W/mK

kAl = 232.6 W/mK

A = Cross sectional area of the fin, A= m2

6. The rate of heat transfer from the fin (Q) =

Where, K = thermal conductivity of air (at mean film temperature)

7. Efficiency of the fin =

Where, L = Length of fin = 1.5 cm

8. Predicted temperature at each point

At starting point T1, T1 (Pr)=

T2 (Pr) = + T6

T3 (Pr) = + T6

T4 (Pr) = + T6

T5 (Pr) = + T6

40

Where, X2 = 2.5 cm, X3 = 5 cm, X4 = 7.5 cm, X5 = 10 cm, L = 15cm

41

Length of the fin cm

Temperature in oC

Predicted

Observed

Length of the fin cm

Tem

pera

ture

in o C

Predicted

Observed

42

Forced Convection

1. T average = oC

2. Tmf = mean film temperature = oC

3. Discharge of air, m3/sec

Where, Cd = Co-efficient of discharge of air = 0.64

A = Cross sectional area of the orifice = in m2

g = Acceleration due to gravity = 9.81m/s2

hm = Difference in manometer reading in metre

w = Density of water = 1000kg/m3

a = Diameter of the orifice = 1.810-2 metre

4. Velocity of air in duct (VD) at T6 oC

m/sec

Q = Discharge of air in m3/sec

A = Duct area = 0.15 0.10 m2

5. Velocity of air (Vmf) at mean film temperature Tmf oC

m/sec

6. Heat transfer coefficient, h =

Where, d = Diameter of the fin, 1.27 10-2 m

Nu = 0.615 (Re)0.466 when 40<Re<4000

7. m-1

Where, h = heat transfer coefficient, W/m2K

P = Circumference of the fin = d, m

K = Thermal conductivity of the material (Given specimen)

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A = Cross sectional area of the fin = in m2

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8. The rate of heat transfer from the fin,

Nu = 0.174(Rc)0.618 when 40 < Rc >40000

Re = Reynold’s number =

d = Diameter of the orifice= 1.8 x 10-2 m

= Kinematic viscosity (m2 /sec) at Tmf

9. Efficiency of the fin =

Where, L=Length of = 1.5 cm

10. Predicted temperature at each point

At starting point T1, T1=15

T2 (Pr) = + T6

T3 (Pr) = + T6

T4 (Pr) = + T6

T5 (Pr) = + T6

Where, X2 = 2.5 cm, X3 = 5 cm, X4 = 7.5 cm, X5 = 10 cm, L = 15cm

46

Length of the fin cm

Tem

pera

ture

in o C

Predicted

Observed

47

Temperature Distribution

Result

Thus the temperature distribution along the length of a pinfin in natural and forced

convention is determined and effectiveness is also determined.

48