lab manual heat transfer iii b. tech ii...

HEAT TRANSFER LAB

LAB MANUAL

HEAT TRANSFER

III B. TECH II SEM

HEAT TRANSFER LAB

DEPARTMENT

OF

MECHANICAL ENGINEERING

NAME OF THE LABORATORY : HEAT TRANSFER

YEAR & SEM : IV B.TECH I SEM

LAB CODE : ME604PC

HOD PRINCIPAL

HEAT TRANSFER LAB

INDEX

S. No. Contents Page No.

1 Vision & Mission 4

2 Program Educational Objectives 5

3 Program Outcomes 6

4 Program Specific Outcomes 7

5 Course Objectives & Course Outcomes 8

6 University Syllabus 9

7 Lab Instructions 10

8 Composite Slab Apparatus – Overall heat transfer co-efficient 11

9 Heat Transfer through lagged pipe 15

10 Heat Transfer through a Concentric Sphere 18

11 Thermal Conductivity of given metal rod 21

12 Heat Transfer in pin-fin 25

13 Experiment on Transient Heat Conduction 34

14 Heat Transfer in forced convection apparatus 37

15 Heat Transfer in natural convection 45

16 Parallel and Counter Flow Heat exchanger 51

17 Emissivity apparatus 60

18 Stefan Boltzmann Apparatus 62

19 Study of Heat pipe and its demonstration 68

20 Film and Drop wise condensation apparatus 71

21 Critical Heat flux apparatus 74

HEAT TRANSFER LAB

VISION & MISSION

VISION

Mechanical Engineering Department of KG REDDY College of Engineering & Technology strives to

be recognized globally for imparting outstanding technical education and research leading to well

qualified truly world class leaders and unleashes technological innovations to serve the global society

with an ultimate aim to improve the quality of life.

MISSION

Mechanical Engineering Department of KGRCET strives to create world class Mechanical Engineers

by:

Imparting quality education to its students and enhancing their skills.

Encouraging innovative research and consultancy by establishing the state of the art research

facilities through which the faculty members and engineers from the nearby industries can actively

utilize the established the research laboratories.

Expanding curricula as appropriate to include broader prospective.

Establishing linkages with world class R&D organizations and leading educational institutions in

India and abroad for excelling in teaching, research and consultancy.

Creation of service opportunities for the up-liftment of society at large.

HEAT TRANSFER LAB

PROGRAM EDUCATIONAL OBJECTIVES (PEO’S)

PEOs Description

PEO1 To apply deep working knowledge of technical fundamentals in areas related to thermal,

production, design, materials, system engineering areas of Mechanical Engineering.

PEO2 To develop innovative ideas and fine solutions to various mechanical engineering problems.

PEO3 To communicate effectively as members of multidisciplinary teams.

PEO4 To be sensitive to professional and societal context and committed to ethical action.

PEO5 To lead in the conception, design and implementation of new products, processes, services

and systems.

HEAT TRANSFER LAB

PROGRAM OUTCOMES (PO’S)

PO’s Description

PO1

Engineering knowledge: Apply the knowledge of mathematics, science, engineering

fundamentals, and an engineering specialization to the solution of complex engineering

problems.

PO2

Problem analysis: Identify, formulate, review research literature, and analyze complex

engineering problems reaching substantiated conclusions using first principles of

mathematics, natural sciences, and engineering sciences.

PO3

Design/development of solutions: Design solutions for complex engineering problems

and design system components or processes that meet the specified needs with

appropriate consideration for the public health and safety, and the cultural, societal,

and environmental considerations.

PO4

Conduct investigations of complex problems: Use research-based knowledge and

research methods including design of experiments, analysis and interpretation of data, and synthesis of the information to provide valid conclusions.

PO5

Modern tool usage: Create, select, and apply appropriate techniques, resources, and

modern engineering and IT tools including prediction and modelling to complex

engineering activities with an understanding of the limitations.

PO6

The engineer and society: Apply reasoning informed by the contextual knowledge to

assess societal, health, safety, legal and cultural issues and the consequent

responsibilities relevant to the professional engineering practice.

PO7

Environment and sustainability: Understand the impact of the professional engineering

solutions in societal and environmental contexts, and demonstrate the knowledge of,

and need for sustainable development.

PO8

Ethics: Apply ethical principles and commit to professional ethics and responsibilities

and norms of the engineering practice.

PO9

Individual and team work: Function effectively as an individual, and as a member or

leader in diverse teams, and in multidisciplinary settings.

PO10

Communication: Communicate effectively on complex engineering activities with the engineering community and with society at large, such as, being able to comprehend

and write effective reports and design documentation, make effective presentations,

and give and receive clear instructions.

PO11

Project management and finance: Demonstrate knowledge and understanding of the

engineering and management principles and apply these to one’s own work, as a

member and leader in a team, to manage projects and in multidisciplinary

environments.

PO12

Life-long learning: Recognize the need for, and have the preparation and ability to engage in independent and life-long learning in the broadest context of technological

change.

HEAT TRANSFER LAB

PROGRAM SPECIFIC OUTCOMES (PSO’S)

PSO’s Description

PSO 1 Apply the knowledge in the domain of engineering mechanics, thermal and fluid sciences to

solve engineering problems utilizing advanced technology.

PSO 2 Successfully evaluates the principle of design, analysis and implementation of mechanical

systems / processes which have been learned as a part of the curriculum.

PSO 3 Develop and implement new ideas on product design and development with the help of

modern CAD / CAM tools, while ensuring best manufacturing practices.

HEAT TRANSFER LAB

COURSE OBJECTIVES & COURSE OUTCOMES

HEAT TRANSFER LAB

UNIVERSITY SYLLABUS

HEAT TRANSFER LAB

LAB INSTRUCTIONS

1. Laboratory uniform, shoes are compulsory in the lab.

2. Student should wear college ID-card and must carry record and observation.

3. Take signature of lab in charge after completion of observation and record.

4. If any equipment fails in the experiment report it to the supervisor immediately.

5. Students should come to the lab with thorough theoretical knowledge.

6. Don't touch the equipment without instructions from lab supervisor.

7. Don't crowd around the experiment and behave in-disciplinary.

8. Students should carry their own stationary and required things.

9. Using the mobile phone in the laboratory is strictly prohibited.

HEAT TRANSFER LAB

EXPERIMENT - 1

COMPOSITE SLAB APPARATUS – OVERALL HEAT TRANSFER

COEFFICIENT

AIM:

1. To determine total thermal resistance and thermal conductivity of composite wall.

2. To plot temperature gradient along composite wall structure.

DESCRIPTION:

The apparatus consists of a central heater sandwiched between two sheets. Three types of slabs are

provided both sides of heater, which forms a composite structure. A small hand press frame is provided

to ensure the perfect contact between the slabs. A dimmerstat is provided for varying the input to the

heater and measurement of input is carried out by a voltmeter, ammeter.Thermocouples are embedded

between interfaces of the slabs, to read the temperature at the surface.

The experiments can be conducted at various values of input and calculation can be made accordingly.

SPECIFICATIONS:

1. Slab assembly arranged symmetrically on both sides of heater.

2. Heater: Nichrome heater wound on mica former and insulation with control unit capacity 300

W maximum.

3. Heater Control Unit: 0-230V. Ammeter 0-2Amps. Single phase dimmerstat (1No.).

4. Voltmeter 0-100-200V. Ammeter 0-2Amps.

5. Temperature Indicator (digital type): 0-200oC. Service required – A. C. single

phase 230 V. earthed electric supply.

6. Type of Thermocouple: Copper/Constantan wire

HEAT TRANSFER LAB

SCHEMATIC DIAGRAM:

(11) Thermocouple Socket (T1 To T6 Thermocouple Positions)

(1) Hand Wheel (2) Screw

(3) Cabinet (4) Fabricated Frame

(5) Acrylic Sheet (6) Press Wood Plate

(7) Bakelite Plate (8) C.I. Plate

(9) Heater (10) Heater Cable

HEAT TRANSFER LAB

SAMPLE CALCULATIONS:

Determine the unknown thermal conductivity of press wood:

Total amount of heat delivered to the slab = 40 W

Since the heater is positioned at the center and similar slabs are fixed on either side. Therefore, amount

of heat transferred to the RHS portion of the composite slab will be

4020

2Q W= =

1T 126= , 2T 123= , 3T 82= , 4T 80= , 5T 60= , 6T 59=

( )1 5T T T 126 60 66∆ = − = − =

1x 12mm 0.012m= = ; o1k 52W /m C= − (cast iron)

2x 12mm 0.012m= = ; o2k 1.4W /m C= − (bakelite)

3x 12mm 0.012m= = ; o3k ? W /m C= − (press wood)

Heat transfer area (i.e. area of the slab perpendicular to the direction of heat flow)

2 22D 3.17 0.15

A 0.0177m4 4

π ×= = =

Heat flux, 2Q 1

q 1130W/mA 0.0177

= = =

3 1 2

3 1 2

x x xT

K q K K

∆= − +

( )3

0.0125 66 0.0125 0.0125

K 1130 52 4= − +

3K 0.24W / m C= −�

Literature value of thermal conductivity of press wood lies between 0.1 & 0.27 W/m-oC

HEAT TRANSFER LAB

Composite Wall Apparatus

Plate Diameter (m) Thickness (m) Area (m2) Thermal

Conductivity

Cast Iron 0.15 0.0125 0.000127 82

Bakelite 0.15 0.0125 0.000127 1.4

Press Wood 0.15 0.0125 0.000127 0.12

CALCULATION FOR K3 PRESSWOOD VALUE

S. No.

Heat Input

T1 T2 T3 T4 T5 T6 3 1 2

3 1 2

x x xT

K q K K

∆= − +

V I Q = V x I

EXAMPLE 1 220 0.18 40 126 125 93 91 60 58 3K 0.24W / m C= −�

EXAMPLE 2

1

2

HEAT TRANSFER LAB

EXPERIMENT – 2

HEAT TRANSFER THROUGH LAGGED PIPE

AIM:

1. To determine heat flow rate through the lagged pipe and compare it with the heater for known value of

thermal conductivity of lagging material.

2. To determine the thermal conductivity of lagging material by assuming the heater input to be the heat

flow rate through lagged pipe.

DESCRIPTION:

The apparatus consists of three concentric pipes mounted on suitable stand. The inside pipe consists of

a heater, which is wound with nichrome wire on the insulation. Between first two cylinders the

insulating material with which lagging is to be done is filled compactly. Between second and third

cylinders another material used for lagging is filled. The thermocouples are attached to the surface of

cylinders approximately to measure the temperatures. The input to the heater is varied through a

dimmerstat and measured on voltmeter and ammeter. The experiments can be conducted at various

values of input and calculations can be made accordingly. Similarly, the experiments can be made for

double or single lagging removing appropriate pipes.

SCHEMATIC DIAGRAM:

1 Outer Pipe

2 Middle Pipe

3 Inside Pipe

4 Heater

5 Support

6 Connection Stirrer

7 Thermocouple Socket

8 Board T1 to T6 Thermocouple Position

HEAT TRANSFER LAB

PROCEDURE:

1. Arrange the pipes in proper fashion with heater assembly (arranged normally).

2. Fill the lagging material in pipes uniformly and by gentle pushing, press the lagging material (filled

normally).

3. See that material gets packed uniformly.

4. Close both ends of pipes and keep the assembly on stands.

5. Start the supply of heater and by varying dimmerstat adjusts the input for desired value (Range 60

to 120 watts) by using voltmeter and ammeter.

6. Take readings of all the 6 thermocouples at an interval of 5 minutes until the steady state is

reached.

7. Note down steady readings in observation table.

LIMITS AND PRECAUTIONS:

1. Keep dimmer stat to zero position before start.

2. Increase voltage gradually.

3. Keep the assembly undisturbed while testing.

4. While removing or changing the lagging material, do not disturb the thermocouples.

5. Do not increase power above 100 Watts.

6. Operate selector switch of temperature indicator gently.

OBSERVATIONS:

Di = Inner Diameter of pipe = 0.032 m

Do = Outer Diameter of pipe = 0.080 m

L =Length of Pipe= 0.4 m

OBSERVATION TABLE:

S. No. Voltmeter V Current I Q = V x

I

Thermocouple Readings in oC

T1 T2 T3 T4 T5 T6

1

2

3

4

CALCULATIONS:

Qa = Actual heat Input in Watts

Qact = V x I

Where,

V = Voltage in volts

I = Current in Amperes

Mean temperature readings in 0C

HEAT TRANSFER LAB

1 2 3T T TT(inside)

2

+ +=

4 5 6T T TT(outer)

2

+ +=

K1 = Thermal Conductivity of Inner material in W / m K

( )

oa

i1

i o

rQ ln

rK

2 L T Tπ

×

=−

Where,

ri = Radius of Inner Pipe in meter

ro = Radius of middle pipe in meter

L= Length of Pipe in meter

CONCLUSION:

1. Heat flow rate through the lagged pipe and compare it with the heater for known value of

thermal conductivity of lagging material is found out to be -----

2. Thermal conductivity of lagging material by assuming the heater input to be the heat flow rate

through lagged pipe is found out to be ---------------

HEAT TRANSFER LAB

EXPERIMENT – 3

HEAT TRANSFER THROUGH A CONCENTRIC SPHERE

AIM:To find out the thermal conductivity of concentric sphere (Powder)

DESCRIPTION:

The apparatus consists of two thin walled concentric copper spheres. The inner sphere houses the

heating coil. The insulating powder (Asbestos powder – Lagging Material) is packed between the two

shells. The powder supply to the heating coil is by using a dimmerstat and is measured by Voltmeter

and Ammeter. ChoromelAlumel thermocouples are used to measure the temperatures. Thermocouples

(1) to (4) are embedded on inner sphere and (5) to (10) are as shown in the fig. Temperature readings in

turn enable to find out the Thermal Conductivity of the insulating powder as an isotropic material and

the value of Thermal Conductivity can be determined.

Consider the transfer of heat by conduction through the wall of a hollow sphere formed by the

insulating powdered layer packed between two thin copper spheres (Ref. Fig. 1)

Let, ri = radius of inner sphere in meters.

ro = radius of outer sphere in meters.

Ti = average temperature of inner sphere in oC.

To = average temperature of outer sphere in oC.

Where,

1 2i

T TT

2

+= and 3 4

o

T TT

2

+=

Note that T1 to T10 denote the temperature of thermocouples (1) to (10).

From the experimental values of q, Ti and To the unknown thermal conductivity K can be determined as

( )( )

o i

i o i o

q r rK

4 r r T Tπ

−=

× +

SPECIFICATIONS:

1. Radius of the inner copper sphere, ri = 50mm

2. Radius of the outer copper sphere, ro = 100mm

3. Voltmeter (0 – 100 – 200 V).

4. Ammeter (0 – 2 Amps.)

5. Temperature Indicator 0 – 300 0C calibrated for chromelalumel.

6. Dimmerstat 0 – 2A, 0 – 230 V.

HEAT TRANSFER LAB

7. Heater coil - Strip Heating Element sandwiched between mica sheets – 200 watts.

8. ChromelAlumel Thermocouples – No. (1) and (2) embedded on inner sphere to measure Ti.

9. ChromelAlumel Thermocouples – No. (3) and (4) embedded on outer sphere to measure To.

10. Insulating Powder – Plaster of Paris commercially available powder and packed between the two spheres.

SCHEMATIC DIAGRAM:

EXPERIMENTAL PROCEDURE: 1. Start main switch of the control panel. 2. Increase slowly the input to the heater by the dimmerstat starting from zero volt position. 3. Adjust input equal to 40 W max by voltmeter and ammeter. Wattage Q = VI 4. See that this input remains constant throughout the experiment. 5. Wait till fairly steady state condition is reached. This can be checked by reading temperatures of

thermocouples (1) to (10)and note changes in their readings with time. 6. Note down the readings in the observation table as given below.

CALCULATION:

W = V x I Watts.

HEAT TRANSFER LAB

Ti = Inner sphere mean temp. 0C

To = Outer sphere mean temp. 0C

ri = Radius of inner copper sphere = 50 mm. or 0.05m

ro = Radius of outer copper sphere = 100 mm. or 0.1m

Using Equation:

q V I W /m K= × −

( )( )

o i

i o i o

q r rK

4 r r T Tπ

−=

× −

CONCLUSION:

Thermal conductivity of powder is found out to be ____

SPECIMEN CALCULATIONS:

1 2i

T T 142 140T 141

2 2

+ += = =

3 4o

T T 47 49T 48

2 2

+ += = =

( )( )

( )( )

o i

i o i o

q r r 30 0.1 0.05K 0.256 W/m K

4 r r T T 4 3.14 0.05 0.1 141 48π

− −= = =

× − × × × × −

Actual value of gypsum plaster of Paris = 0.22 W/m-K

Thermal Conductivity of Powder

Inner Ball Dia 0.1 m

Outer Ball Dia 0.2 m

S. No. q

(W)

Inner Ball Temperature Outer Ball Temperature ( )

( )o i

i o i o

q r rK

4 r r T Tπ

−=

× −

T1 T2 1 2

i

T TT

2

+= T3 T4

3 4o

T TT

2

+=

EXAMPLE 1 30 142 142 141 47 49 48 0.256

EXAMPLE 2

1

2

HEAT TRANSFER LAB

EXPERIMENT – 4

THERMAL CONDUCTIVITY OF GIVEN METAL ROD

AIM:To determine the thermal conductivity of a good conductor material, say brass.

THEORY:

From Fourier’s law of heat conduction

dTq ka

dx= − , k = thermal conductivity of material.

Thermal conductivity is a property of a material and is defined as the amount of heat conducted across a

unit area per unit time when temperature gradient is unity.

DESCRIPTION:

The apparatus consists of a metal bar, one end of which is heated by an electric heating coil while the

other end projects inside the cooling water jacket. The middle portion of the rod is surrounded by an

insulating material like asbestos to minimize lateral heat transfer from the rod and thus ensure a more

nearly constant temperature gradient throughout the length of the rod. The temperature of the bar is

measured at five different locations while the radial temperature distribution is measured by separate

thermocouples at two different sections in the insulating shell. The heater is provided with a dimmerstat

for controlling the heat input water can be circulated through the jacket and it’s flow rate and

temperature rise can be noted down.

The assumption that at steady state, the heat flow is mainly due to axial conduction can be verified by

the readings of temperature sensors fixed in the insulation material around the rod in radial direction.

Less variation in these readings shall confirm the assumption.

The value of dT/dX / X = L is obtained at the slope of the graph between T vs X

ToC

X = 0 X, mm X = L

Temp Sensor No. along with axis Distance from leading edge (hot end) of the rod. X, mm

T1 50

T2 100

HEAT TRANSFER LAB

T3 150

T4 200

SCHEMATIC DIAGRAM:

PROCEDURE:

1. Connect the equipment to the power supply.

2. Give heat input to the heater by slowly rotating the dimmerstat and adjust the voltage to say (S25W,

50W etc)

3. Start the cooling water supply through the jacket and adjust it to some value.

4. Allow sufficient time to reach study state conditions.

5. Note down the temperature from 1 to 6 and also the mass flow rate of water.

6. Repeat the experiment for other heat inputs.

7. Repeat the experiment at different heat inputs (Do not exceed 50w).

HEAT TRANSFER LAB

SPECIFICATIONS:

OBSERVATION:

S. No.

Heat Input

T1 T2 T3 T4

Water

Inlet

Temp

T5

Water

Outlet

Temp

T6

Flow

rate

of

water ( )

pmc TK

DTADx

∆=

Q I Q = V

x I

EXAMPLE

1 220 0.46 101 168 142 98 72 25 27

1 liter

150

sec =

0.0025

kg/sec

436 W/m-K

1

2

3

Graph for (DT/DX)

T1 T2 T3 T4 X1 X2 X3 X4

168 142 98 72 0.05 m 0.1 m 0.15 m 0.2 m


Draw the variation of temperature along the length of the bar from the graph df

294dx

=

Heat flowing out of the bar = Heat carried away by the cooling water

( )pw outlet inletdt

KA mC T Tdx

= −

A = Area of the metal rod

Length of the metal bar 300 mm

Diameter of the metal bar 25 mm

Test length of the bar 200 mm

Temperature sensors in the setup 6 No’s

Temperature sensors mounted on the bar 4 No’s

Temperature sensors mounted on the water jacket 2 No’s

Types of temperature sensors Copper/Constantan wire

Heater coil Nichrome heater

Cooling jacket diameter 125 m

Length of cooling jacket 50 mm

Heater to distance thermocouple T1 50 mm




HEAT TRANSFER LAB

2

2 2d0.025 0.000490m

4 4

π π= = × =

Mass flow rate of cooling water, 3

wkg

m 2.5 10sec

−= ×

Specific heat of water, pwC 4187 J /kg K= −�

( )pw outlet inletdt

KA mC T Tdx

= −

( )3K 0.00049 294 2.5 10 4187 25 27−× × = × × × −

K 145 W /mK=

HEAT TRANSFER LAB

EXPERIMENT – 5

HEAT TRANSFER IN PIN – FIN

AIM:

1. To draw the variation of temperature along the length of pin fin under forced convection.

2. To determine the value of heat transfer coefficient under forced condition and to find:

a) Theoretical value of temperatures along the length of the fin

b) Effectiveness and efficiency of the pin – fin for insulated and boundary condition

THEORY:

The heat transfer from a heated surface to the ambient is given by q hA T= ∆ . In this relation, h is the

heat transfer coefficient. T∆ is the temperature difference and A is the area of heat transfer. To

increase q, h may be increased or surface area may be increased. In some cases, it is not possible to

increase the value of heat transfer coefficient and the temperature difference T∆ and thus the only

alternative is to increase the surface area of heat transfer. The surface area is increased by attaching

extra material in the form of rod (circular or rectangular) on the surface where we have to increase

the heat transfer rate. This extra material attached is called the “extended surface or fins”.

The fins may be attached on a plane surface, known as plane surface fins. If the fins are attached on

the cylindrical surface, they are called circumferential fins. The cross – section of the fin may be

circular, rectangular, triangular or parabolic.

Temperature Distribution along the length of the fin is ( )

o o

cosh m L xT T

T T cosh mL

θθ

∞

∞

−−= =

−

where, T = temperature at any distance x on the fin

To = temperature at x = 0

T∞ = ambient temperature

L = length of the fin

hcP

mKA

=

hc = convection heat transfer coefficient

P = perimeter of the fin

A = area of the fin

K = thermal conductivity of the fin

Heat flow, oq hcPKA tanh mLθ=

Effectiveness of a fin is defined as the ratio of heat transfer with fin to the heat transfer from the

surface without fins.

HEAT TRANSFER LAB

For end insulated condition

oo

hcPKA tanh mL PKtanh mL

hcA hcAε θ

θ= =

The efficiency of a fin is defined as the ratio of the actual heat transferred by the fin to the maximum

heat transferred by the fin if the entire fin area were at base temperature.

tanh mL

mLη =

SPECIFICATIONS:

Length of the fin 150 mm

Diameter of the fin 12 mm

Thermal conductivity of fin material (brass) 110 W/m-K

Diameter of the orifice 0.02 m

Duct length 0.5 m

Diameter of the duct 0.15 m

Area of the duct 0.0177 m2

Coefficient of discharge of the orifice 0.68

Density of manometric fluid ( Water) 13.6 x 103 kg/m3

Type thermocouple Copper/Constantan wire

Heater to Thermocouple T1 distance 25 mm




SCHEMATIC DIAGRAM:

HEAT TRANSFER LAB

PROCEDURE:

1. Connect the equipment to electric power supply.

2. Keep the thermocouple selector switch to zero position.

3. Turn the dimmerstat knob clockwise and adjust the power input to

the heater to the desired value.

4. Switch on the blower.

5. Set the airf flow rate to any desired value by adjusting the difference in mercury levels in the manometer.

6. Allow the unit to stabilize. 7. Turn the thermocouple selector switch clockwise and note down the

temperature T1 to T6. 8. Note down the difference in level of manometer.

9. Repeat the experiment for different power input to the heater.


Velocity at orifice = ( )m a

o d 4a

2ghV C

1

ρ ρ

ρ β

−=

−

HEAT TRANSFER LAB

HEAT TRANSFER LAB

DESCRIPTION

HEAT TRANSFER LAB

HEAT TRANSFER LAB

SPECIFICATIONS:

HEAT TRANSFER LAB

HEAT TRANSFER LAB

PARALLEL FLOW & COUNTER FLOW HEAT EXCHANGER

INTRODUCTION

Heat Exchangers are devices in which heat is transferred from one fluid to another. The necessity for

doing this arises in a multitude of industrial applications. Common examples of heat exchangers are

the radiator of a car, the condenser at the back of a domestic refrigerator and the steam boiler of a thermal power plant.

Heat Exchangers are classified in three categories:

1. Transfer Type

2. Storage Type

3. Direct Contact Type

A transfer type of heat exchanger is one on which both fluids pass simultaneously through the device

and heat is transferred through separating walls. In practice most of the heat exchangers used are

transfer type one.

The transfer type exchangers are further classified according to flow arrangement as :

3. PARALLEL FLOW in which fluids flow in the same direction.

4. COUNTER FLOW in which they flow in opposite direction, and

5. CROSS FLOW in which they flow at right angles to each other.

A simple sample of transfer type of heat exchanger can be in the form of a tube type arrangement in which one of the fluids is flowing through the inner tube and the other through the annulus

surroundings. The heat transfer takes place across the walls of the inner tube.

The apparatus consists of a tube in tube type concentric tube heat exchanger. The hot fluid is hot water

which is obtained through Running Geezer the inner tube & the cold fluid is cold water flowing

through the Tap.The hot water flows always in one direction and the flow rate of which is controlled

by means of a valve. The cold water can be admitted at one of the end enabling the heat exchanger to

run as a parallel flow apparatus or a counter flow apparatus. This is done by valve operations.

Thermocouple type sensors measure the temperature. For Flow measurement of water are provided at

inlet of cold water and outlet of hot water line. The readings taken time through 1 Litre Beaker.

SPECIFICATIONS

i) Inner Tube Material : I.D. 15mm

ii) Outer tube Material : I.D. 28 mm

iii) Length of the Heater Exchanger: L = 1.2 m

HEAT TRANSFER LAB

iv) Temperature Controller : Digital 0-200oC

v) Temperature Indicator : Digital 0-199.9oC and least count

0.1oC with multichannel switch.

vi) Temperature Sensors : Thermocouple (5 Nos.)

EXERIMENTAL PROCEDURE

1. Put water in bath and switch on the heaters.

2. Adjust the required temperature of hot water using DTC.

3. Adjust the valve. Allow hot water to recycle in bath through by-pass by switching on the

Geezer.

4. Start the flow through annulus and run the exchanger either as parallel flow unit.

5. Adjust the flow rate on cold water side taken time through 1 Liter Biker.

6. Adjust the flow rate on hot water side taken time through 1 Liter Biker.

7. Keeping the flow rates same, wait till the steady state conditions are reached.

8. Taken the temperature on hot water and cold water side and also the flow rates accurately.

9. Repeat the experiment with a counter flow under identified flow conditions.

HEAT TRANSFER LAB

Note that in a special case of Counter Flow Exchanger exists when the heatcapacity rates Cc & Ch are

equal, then Thi – Tco = Tho – Tci thereby making DTi =

HEAT TRANSFER LAB

HEAT TRANSFER LAB

EXPERIMENT – 10

EMISSIVITY MEASUREMENT APPARATUS

AIM

To find the emissivity of given surface plate

APPARATUS

The experimental setup consists of two aluminum plates, one of them is used as black surface and the other as

test plate. Both the plates are heated by separate heating elements and kept in a closed box, which establishes

undisturbed natural convection surroundings. Power supply to each plate is varied using dimmerstats and

measured by a voltmeter and ammeter. Temperature of plates is measured by means of two thermocouples and

temperature of ambient is measured by a third thermocouple.

SPECIFICATIONS

Diameter of plates = 150 mm

Area of plates = 0.0177 m2

Dimmerstat = 200 W

Digital Voltmeter = 500 V

Digital Ammeter = 5 A

Thermocouple material = Copper Constantan

Digital temperature indicator (capable of measuring upto 999o C)

PROCEDURE

1. Gradually increase the heater input to the black plate and adjust it to some value viz. 30 – 40 W and adjust the heater input to test plate slightly less than the black plate viz. 27 – 35 W.

2. Check the temperature of the two plates with small time intervals and adjust the input of the test plate

only, using the dimmerstat so that the two plates will be maintained at the same temperature.

3. This will require some trial and error and one has to wait sufficiently to obtain the steady state

condition.

4. After attaining the steady state condition record the temperatures, voltmeter and ammeter readings for

both the plates.

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

PRECAUTIONS

1. Always keep dimmerstat at zero before starting.

2. Increase power input slowly.

3. Do not touch black plate.

4. Use stabilized electric supply.

OBSERVATION

S. No. BLACK PLATE TEST PLATE ENCLOSURE TEMP

V1 I1 Tb V2 I2 TT Tao C

1

2

3

CALCULATIONS 4 4

1 2( ) ( ) ( )b T T bQ Q E E A T Tσ− = − −

In SI units, 8 2 45.67 10 /W m Kσ −= ×

E = emissivity of specimen to be determined (absorption)

Given that:

HEAT TRANSFER LAB

Q1 = black plate = 40 W

Q2 = test plate = 38 W

Test plate temp. ( ) 143 273 416TT C K= + =�

Surrounding temp. ( ) 40 273 313sT C K= + =�

4 4

1 2( ) ( ) ( )b T T bQ Q E E A T Tσ− = − −

8 4 4(40 38) (1 ) 5.67 10 0.0154 (416 313 )TE −− = − × × × × −

2 (1 ) 17.76TE= − ×

0.88TE =

RESULT

Hence the emissivity of the test plate is determined.

HEAT TRANSFER LAB

Experiment – 11

Stefan Boltzmann Apparatus

HEAT TRANSFER LAB

HEAT TRANSFER LAB

SAMPLE CALCULATIONS:

= 5.55 x 10-8 w/m2.K4

HEAT TRANSFER LAB

HEAT TRANSFER LAB

Experiment – 12

STUDY OF HEAT PIPE AND ITS DEMONSTRATION

HEAT TRANSFER LAB

HEAT TRANSFER LAB

Experiment – 13

FILM AND DROPWISE CONDENSATION APPARATUS

AIM: To determine dryness friction of steam by drop wise and film wise condensation.

DESCRIPTION:

SPECIFICATIONS:

PROCEDURE:

HEAT TRANSFER LAB

CALCULATIONS:

The total heat before dropwise condensation = The total heat after dropwise condensation.

p1 + x = p2 + Cp (t1 – t2)

x = p2 + Cp (t1 – t2) - p1

EXAMPLE:

x = p2 + Cp (t1 – t2) - p1

p1 = 1.241

p2 = 2.5

Cp = 0.24

t1 = 88

HEAT TRANSFER LAB

t2 = 68

x = 1.241 + 0.24 (88 – 68) - 2.5

x = 3.54

HEAT TRANSFER LAB

Experiment – 14

CRITICAL HEAT FLUX

AIM: To visualize the pool boiling over the heater wire in different regions upto the critical heat flux point at

which the wire melts.

INTRODUCTION:

When heat is added to a liquid from a submerged solid surface, which is at a temperature higher than the

temperature of the liquid, it is usual for a part of the liquid to change phase. This change of phase is called

boiling.

Boiling is of various types, the type depends upon the temperature difference of the surface and the liquid. The

different types are indicated in which a typical experimental boiling curve obtained in a saturated pool of liquid

is down.

DESCRIPTION:

The apparatus consists of a cylindrical glass container housing and test heater (Nichrome wire). Test heater is

connected also to mains via a dimmer. An ammeter is connected in series while a voltmeter across it to the read

the current and voltage. The glass container is kept on a stand, which is fixed on a metallic platform. There is

provision of illuminating the test heater wire with the help of a lamp projecting light from back and the heater

wire can be viewed through a lens.

This experimental setup is designed to study the pool – boiling phenomenon upto critical heat flux point. The pool boiling over the heater wire can be visualized in the different regions upto the critical heat flux point at

which the wire melts. The heat flux from the wire is slowly increased by gradually increasing the applied

voltage across the test wire and the change over from natural convection to nucleate boiling can be seen.

The formation of bubbles and their growth in size and number can be visualized followed by the vigorous

bubble formation and their immediate carrying over to surface and ending this in the braking of wire indicating

the occurrence of critical heat flux point.

SPECIFICATION:

• Glass container : Dia 150 mm & Height 200 mm

• Nichrome wire size : 0.135 F mm

• Dimmer stat : 10 Amp, 230 volts

• Voltmeter : 0 to 250 V

• Ammeter : 0 to 10 AMP

• Thermometer : 0 to 100o

• Nichrome wire resistance : 6.4 ohms

HEAT TRANSFER LAB

SCHEMATIC DIAGRAM:

THEORY:

The heat flux supplied to the surface is plotted against (Tw - Ts), the difference between the temperature of the surface and the saturation temperature of the liquid. It is seen that the boiling curve can be divided into three

regions:

• Natural convection region

• Nucleate boiling region

• Film boiling region

The region of natural convection occurs at low temperature differences (of the order of 10oC or less). Heat

transfer from the heated surface to a liquid in its vicinity causes the liquid to be superheated. The superheated

liquid rises to the free liquid surface by natural convection, where vapour is produced by evaporation. As the

temperature difference (Tw - Ts) is increased, nucleate boiing starts. In this region, it is observed that the

bubbles start to form at certain locations on the heated surface.

Region II consists of two parts. In the first part, II – a, the bubbles formed are very few in number. They

condense in the liquid and do not reach the free surface. In the second part, II – b, the rate of bubbles formation

and the number of locations where they are formed increase. Some of the bubbles now rise all the way to the

free surface. With increasing temperature difference, a stage is finally reached when the rate of formation of

bubbles Is so high, that they start to coalesce and blanket the surface with a vapor film. This is the beginning of

the region III viz film boiling.

In the first part of this region III – a, the vapour film is unstable, so that the film boiling may be occurring on a

apportion of the heated surface area, while nucleate boiling may be occurring on the remaining area. In the

second part, III – b, a stable film covers the entire surface. The temperature difference in this region is of the

order of 1000o C and consequently radiative heat transfer across the vapor film is also significant.

HEAT TRANSFER LAB

It will be observed that the heat flux does not increase in a regular manner with the temperature difference. In

region I, the heat flux is proportional to (Tw - Ts)n, where ‘n’ is slightly greater than unity. When the transition

from natural convection to nucleate boiling occurs the heat flux starts to increase more rapidly with temperature

difference, the value of n increasing to about 3. At the end of region II, the boiling curve reaches a peak.

Beyond this, in the region II – A, inspite of increasing temperature difference, the heat flow increases with the

formation of a vapor film. The heat flux passes through a minimum at the end of region III – a. it starts to

increase again with(Tw - Ts) only when stable film boiling begins and radiation becomes increasingly

important.

It is of interest to note how the temperature of the heating surface changes as the heat flux is steadily increased

from zero. Upto point A, natural convection boiling and nucleate boiling occur and the temperature of the

heating surface is obtained by reading off the value of (Tw - Ts) from the boiling curve and adding to it the

value of Ts.

If the heat flux is increased even a little beyond the value of A, the temperature of the surface will shoot up to

the value corresponding to the point C. It is apparent from figure 1 that surface temperature corresponding to

point C is high.

For most surfaces, it is high enough to cause the material to melt. Thus in most practical situations, it is

undesirable to exceed the value of heat flux corresponding to point A. This value is therefore of considerable

engineering significance and is called the critical or peak heat flux. The pool boiling curve as described above is

known as Nukiyam pool boiling curve. The discussions so far has been concerned with the various type of

boiling which occur in saturated pool boiling. If the liquid is below the saturation temperature we say that sub-

cooled pool boiling is taking place. Also in many practical situations, e.g. steam generators; one is interested in boiling in a liquid flowing through tubes. This is called forced convection boiling, may also be saturated or sub

– cooled and of the nucleate or film type.

Thus in order to completely specify boiling occurring in any process, one must state

Whether it is forced convection boiling or pool boiling,

Whether the liquid is saturated or sub – cooled, and

Whether it is in the natural convection nucleate or film boiling region.

PROCEDURE:

• Fill the tank with water.

• Dip the nichrome wire into the water and make the electrical connections.

• Note the current reading in steps of 1 Amp till a maximum current of 10 Amp.

• Between each reading the time interval of two min is allowed for steady state to establish.

• Water temperature is noted with a thermometer at the beginning and at the end of the experiment. The

average of these two is taken as the bulk liquid average temperature.

OBSERVATIONS:

d = Diameter of test wire = 0.135 x 10-3 m

L = Length of the test heater = 0.088 m

A = Surface area = PdL = 3.7322 x 10-5 m2

HEAT TRANSFER LAB

OBSERVATIONS TABLE:

S.No. Water/Bulk Temp To C Voltage (V) Ampere (I)

1

2

3

CALCULATION:

• Q = heater power in Watts

Q = V x I Watts

• q = critical heat flux in w/m2

q = Q/A W/m2 PRECAUTIONS:

• Keep the variac to zero voltage postion before starting the experiment.

• Take sufficient amount of distilled water in the container so that both the heaters are completely

immersed.

• Connect the test heater wire across the studs tightly.

• Do not touch the water or terminal points after putting the switch in on position.

• Very gently operate the variac in steps and allow sufficient time in between.

• After the attainment of critical heat flux condition, slowly decrease the voltage and bring it to zero.

CONCLUSION:

Heater wire in different regions upto the critical heat flux point at which the wire melts is found out to be _____

lab manual heat transfer iii b. tech ii...

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