heat transfer manual for printing

8/11/2019 Heat Transfer Manual for Printing

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Laboratory Manual

For

HEAT TRANSFER

ME F311

BY

DEPARTMENT OF MECHANICAL ENGINEERING

EDUCATIONAL DEVELOPMENT DIVISIONBirla Institute of Technology & Science, Pilani K.K. Birla Goa Campus

GOA- 403 726

2014-2015


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Laboratory Manual

For

HEAT TRANSFER

ME F311

BY

DEPARTMENT OF MECHANICAL ENGINEERING

EDUCATIONAL DEVELOPMENT DIVISIONBirla Institute of Technology & Science, Pilani K.K. Birla Goa Campus

GOA- 403 726

2014-2015


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LIST OF EXPERIMENTS

S. No. Title of the Experiment Page No.

No. of

Tear off

Sheets

Thermal Science Lab (A110)

1 Heat Transfer through Lagged Pipe 1-4 1

2 Stefan Boltzmann Apparatus 5-7 1

3 Emissivity Measurement Apparatus 8-10 1

4 Heat Transfer in Natural Convection 11-13 1

5 Drop wise and Film Condensation 14-20 2

6 Heat Transfer from a Pin Fin 21-26 1

7 Thermal Conductivity of Liquids 27-30 1

8 Thermal Conductivity of Insulating Powder 31-33 1

9 Heat Transfer in Forced Convection 34-37 1

10 Heat Pump Trainer 38-41 1

11 To Determine the Coefficient of Performance (COP) of a Vapor

Compressor Trainer42-45 1

12 Vapor Absorption Refrigeration Trainer 46-51 1

13 Air Conditioning Trainer 52-61 5

14 Parallel and Counter Flow Heat Exchanger 62-65 2

15 Shell and Tube Heat Exchanger 66-69 2


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DESCRIPTION OF LABORATORY

Transport Phenomena laboratory is a hands-on investigation of momentum and

heat transfer. Friction factor; conductivity, convective and diffusion coefficient

measurements; velocity and temperature determination, engineering instrumentation and

experimental analysis of data are some of the tasks in this laboratory.

The experiments focus on demonstration or verifying transport phenomena

principles. The scope is limited to one- dimensional systems and experiments in

momentum transfer and heat transfer are included.

Objectives of the Laboratory component

To supplement theory by enhancing the understanding of basic concepts of

momentum and heat transfer operations.

To gain insight and appreciation for the inherent link between theory and

practical.

To reinforce concepts and principles of Transport Phenomena established in

lecture course through hands- on experience and experience with order of

magnitude and exploration of range of applicability of transport models and

predicted behavior.

To illustrate to the students by actual measurements based on experimental work,

some of the basic laws and principles of momentum and heat transfer.

To provide intensive experience in conducting experiments in laboratory,

analyzing and interpreting data.

To provide experience in engineering measurement and experimentation.

In addition, students get experience in technical communication in the form of

written laboratory reports


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The brief focus of the experiments to be conducted in two laboratories is

given below

Fluid Mechanics Laboratory

The momentum transfer experiments in this laboratory are based on portion

studied in the Transport Phenomena- I course. The laboratory has two hydraulic benches,

experimental set up for losses in pipes, Impact of Jet, free and forced vortex. All these set

up can be kept on hydraulic bench to perform experiment. Addition to these, this lab has

got Darcys Law apparatus and Drag coefficient apparatus.

These experiments are aimed to expose the complexities involved in

measurements of fluid variables like pressure drop, velocity, flow rate etc. and the

devices used for these measurements. The experiments are based on application of

Bernoulli Equation, Energy Equation and Boundary Layer Phenomena.

Thermal Science Laboratory

Thermal Transport Phenomena play a key role in the development of almost every

emerging technology. For instance, one of the main factors for the development of faster

microchips that exit today is effective removal of the heat generated within the chips. To

gain understanding of heat transfer in different areas, it is important to have a feel for

heat transfer in several basic situations.

The laboratory has got experiment through which one can learn how to measure

thermal conductivity, heat transfer coefficient and emmisivity. It has two heat

exchangers, drop wise and film wise condensation apparatus. These experiments aimed to

understand heat transfer problem and correlations based on experiments, which is the

only source when approaching a heat transfer problem. Addition to these, this lab has got

Heat pump, Refrigeration (vapor absorption and compression) test rig and Air conditioner

test rig to find their coefficient of performances.


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GENERAL GUIDELINES AND SAFETY MEASURES

1. Wearing of an apron is compulsory. Dress worn by students should not have

loose clothes.

2. Students must be wearing proper shoes while working in the laboratory.

3. It is expected that before coming to the laboratory, the students has gone through

the instruction sheet for the experiment to be performed.

4. All data/readings must be recorded on the pull out sheets given at the end of this

manual.

5. The students should bring calculators and graph papers with them while coming

to the laboratory so that the results of the experiments may be verified.

6. Each group will be held responsible for loss or breakage of equipment checked

out to it.

7. Many of the experiments involve heavy equipment and machinery. Therefore, it

is very important that the safety measures and precautions must be thoroughly

read and adhered to before starting the equipment.

8. At the end of the experiment, ensure that all the valves in the equipment used areclosed and the electric supplies are switched off.


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Heat Transfer Lab Manual

1

Experiment 1

HEAT TRANSFER THROUGH LAGGED PIPE

Objective:

To determine heat flow rate through the lagged pipe for known value of thermal

conductivity of lagging material and get the combined thermal conductivity of lagging

material. Plot the temperature distribution across the lagging material.

Theory:

Consider a long cylinder of inside radius ri, and lengthL. We expose this cylinder to

a temperature differential Ti -TO and see what the heat flow will be. For a cylinder with

length very large compared to diameter, it may be assumed that the heat flow in a radial

direction, so that the only space coordinate needed to specify the system is r. In cylindrical

system the Fouriers law is written

2

2

r

r

dTQ kA

drA rL

dTQ krL

dr

with the boundary conditions

T = Ti at r = ri

T = To at r = ro

The solution to equation is

2

lni o

o i

kL T T Qr r

and the isothermal resistance in this case is

kL

rrR ioth

2

ln

The thermal-resistance concept may be used for multiple-layer cylindrical walls just

as it was used for plane walls. For the two layer system the solution is


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2

1 3

2 1 3 2

2

ln lnB

kL T T Q

r r k r r k

Description:

The apparatus consist of three concentric pipe mounted on suitable stands. The

inside pipe consists of the heater. Between first two cylinders the insulating material with

which lagging is to be done is asbestos and in second and third pipe is wooden dust.

The Thermocouples are attached to the surface of cylinders appropriately to measure

the temperatures. The input to the heater is varied through a dimmerstat and measured on a

voltmeter, ammeter. The experiments can be conducted at various values of input and

calculations can be made accordingly.

Experimental Procedure:

1. Start the supply of heater & by varying dimmerstat adjusts the input for desired values

by using voltmeter and ammeter.

2. Take readings of all the 6 thermocouples at the interval of 10 minutes until the said

steady state is reached.

3. Note down steady state readings in observation table.

(Assumptions: The pipe is so long as compared with diameter that heat flows in radial

direction only in middle half section.)

Formulae:

1. Heat input, Q V I

Experimental heat flow rate through the composite cylinder (for two insulating layers)

1 0 2

2 ( )[ln( / ) / ] [ln( / ) / ]

i o

Exp

m i m

L T TQr r k r r k

2. From known value of heat flow rate, value of combined thermal conductivity, keffof

lagging material can be calculated:

0

2 ( )

ln( / )

eff i o

Exp

i

Lk T TQ

r r


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3

0ln( / )

2 ( )

Exp i

eff

i o

Q r rk

L T T

3. To plot the temperature distribution use formula:-

1

0

ln( / )

ln( / )

i

o i i

T T r r

T T r r

Thus the plot of T Vs r (thickness) can be made for different values of r.

Mean Readings:

Inside, 1 2

2i

T TT

Middle, 3 4

2m

T TT

Outside, 5 60

2

T TT

Nomenclature:

k = thermal conductivity of material, W/ mK

A = heat transfer area, m2

q = heat transfer rate, W

ri = inside radius of the pipe, m

ro = outside radius of the pipe, m

Ti = inside temperature of the pipe,0C

To = outside temperature of the pipe,0C

L = length of the pipe, m

Exercises:

1. Find the heat flow rate through the lagged pipe.

2. Calculate the combined thermal conductivity of lagging material.

3. Plot temperature profile.


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Precautions & Maintenance Instructions:

1. Use the stabilize A.C. Single Phase supply only.

2. Never switch on mains power supply before ensuring that all the ON/OFF switchesgiven on the panel are at OFF position.

3. Voltage to heater starts and increases slowly.

4. Keep all the assembly undisturbed.

5. Never run the apparatus if power supply is less than 180 volts and above than 240 volts.

6. Operate selector switch of temperature indicator gently.

7. Always keep the apparatus free from dust.

There is a possibility of getting abrupt result if the supply voltage is fluctuating or if the

satisfactory steady state condition is not reached.


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Experiment 2

STEFAN BOLTZMANN APPARATUS

Objective:

To study radiation heat transfer by a black body hence finds the Stefan Boltzmann

constant.

Theory:

The most commonly used law of thermal radiation is the Stefan Boltzmann law

which states that emissive power of a black body is proportional to the fourth power of

absolute temperature of the surface and is given by

The constant of proportionally is called the Stefan Boltzmann constant and has the

value of 5.67 x 10-8

W/m2

K4. The Stefan Boltzmann law can be derived by integrating the

Plancks law over the entire spectrum of wavelength from 0 to . The objective of this

experimental set up is to measure the value of this constant fairly closely, by an easyarrangement.

Description:

The apparatus is centered on a flanged copper hemisphere fixed on a flat non-

conducting base plate. The outer surface of hemisphere is enclosed in a metal water jacket

used to heat it to some suitable constant temperature.

One Temperature Sensor is attached to the inner wall of hemisphere to measure its

temperature and to be read by a temperature indicator. The disc, which is mounted in an

insulating bakelite sleeves is fitted in a hole drilled in the centre of the base plate. A

Temperature Sensor is used to measure the temperature of disc i.e. TD. The Temperature

Sensor is mounted on the disc to study the rise of its temperature.

4

bE T


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When the disc is inserted at the temperature TD its temperature increases with timet

since it receives heat by radiation from hemisphere. This timet is used to calculate the

Stefan Boltzmann constant.

The inner surface of hemisphere and base plate forming the enclosure are blacked by

using lamp black to make their absorptivity to be approximately unity. The copper surface of

the disc is also blackened.


1. Heat the water in the tank by the immersion heater up to a temperature of about 70 -

90C.

2. The disc should be removed before pouring the hot water in the jacket.

3. The hot water is to be poured in the water jacket.

4. The hemispherical enclosure and the base plate will come to some uniform

temperature in a short time after filling the hot water in the jacket. The thermal inertia

of hot water is quite adequate to prevent significant cooling in the time required to

conduct the experiment.

5. The enclosure will soon come to thermal equilibrium conditions.

6. The disc is now inserted in the base plate at a time (t = 0) when its temperature is TD.7. Start noting the temperature change for every five second for a minute.

Formulae:

1. = 04 4

( / )

( )

t

D h D

ms dT dt

A T T

2. AD =2

4

Dd

Nomenclature:

AD = Area of disc D, m2

Th = Temperature of hemisphere enclosure,0C

TD = Temperature of disc at time t = 0,0C

m = mass of disc, kg


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s = specific heat of the disc material, kJ/ kg0C

Exercises:

1. Plot a graph temperature of disc Vs time.

2. Determine the value of Stefan Boltzmann constant.

3. Write your comments on the above results.


1. Always use clean water and heater should be completely dipped in the water before

switch ON the heater.

2. Always take the reading for the first min. of the disc while fixing.


4. Never switch on mains power supply before ensuring that all the ON/OFF switches

given on the panel are at OFF position.

5. Voltage to heater should be constant.


7. Never run the apparatus if power supply is less than 180 V and above than 240 V.



10. Dont switch ON the heater before filling the water into the bath.

There is a possibility of getting abrupt result if the supply voltage is fluctuating or if

the satisfactory steady state condition is not reached.


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Experiment 3

EMISSIVITY MEASUREMENT APPARATUS

Objective:

To find out the emissivity of a test plate.

Theory:

An idealized black surface is one, which absorbs all the incident radiation with

reflectivity and transmissivity equal to zero. The radiant energy per unit time per unit area

from the surface of the body is called as the emissive power and is usually denoted by E.

The emissivity of the surface is the ratio of the emissive power of the surface to the

emissive power of a black surface at the same temperature. If is noted by .

b

E

E

For black body absorptivity = 1 and by the knowledge of Kirchoff's Law of

emissivity of the black body becomes unity. Emissivity being a property of the surface

depends on the nature of the surface and temperature. The present experimental set up is

designed and fabricated to measure the property of emissivity of the test plate surface at

various temperatures.

Description:

The experimental set up consists of two circular copper plates identical in size and is

provided with heating coils sand witches. The plates are mounted on bracket and are kept in

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

input to the heater is varied by separate dimmerstat and is measured by using an ammeter

and a voltmeter with the help of double pole double throw switches. The temperature of theplates is measured by Pt-100 sensor. Another Pt-100 sensor is kept in the enclosure to read

the ambient temperature of enclosure.

Plate 1 is blackened by a thick layer of lampblack to form the idealized black surface

where as the plate 2 is the test 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


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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 the cases. When the surface

temperatures are same the difference in the heater input readings is because of the difference

in radiation characteristics due to their different emissivities.


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

adjust heater input to test plate slightly less than the black plate.

2. Take readings of all the 3 thermocouples at the interval of 10 minutes until the said

steady state is reached.

3. After attaining the steady state conditions record the Voltmeter and Ammeter reading for

both the plates.

Specification:

1. Test plate dia = 160 mm

2. Black plate = 160 mm

3. Dimmerstat for both plates = 0-2 A, 0-220V.

4. Voltmeter = 0-250V, Ammeter 0-2.5 A5. RTD Temperature sensor = 3 Nos

6. Heater for test plate and black plate Nichrome strip wound on mica sheet and sand-

witched between two mica sheets of 440 Watt.

Formulae:

1. 4 4b b sq A T T

2. 4 4

t t t sq A T T

3. t = Emissivity of the test plate to be determined.

4 4

4 4

0.86

0.86

b sb

t t t s

A T TW

W A T T


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Nomenclature:

qb = heat input to disc coated with lamp black (W)

= Wb x 0.86

Wb = wattage supplied to black plate

qt = heat input to test plate (W)

= Wtx 0.86

Wt = wattage supplied to test plate

= Stefan Boltzmann Constant = 5.67 10-8 W/ m K4

A = area of disc (m2)

Tb = surface temperature of black plate disc, K

Tt = surface temperature of test plate disc, K

Ts = ambient temperature of enclosure, K

t = emissivity of the test plate to be determined.

b = emissivity of black body.

Exercises:

1. Find the emissivity of the test plate


1. Use the stabilize A.C. Single phase supply only.




4. Keep all the assembly undisturbed.5. Never run the apparatus if power supply is less than 180 volts and above than 240

volts.




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Experiment 4

HEAT TRANSFER IN NATURAL CONVECTION

Objective:

To find out the heat transfer co-efficient of vertical cylinder in natural convection.

Theory:

Natural convection phenomenon is due to the temp. Difference between the surface

and the fluid and is not created by any external agency. The Setup is designed and

fabricated to study the natural convection phenomenon from a vertical cylinder in terms of

average heat transfer coefficient.

The heat transfer coefficient is given by.

( )

a

s a

Qh

A T T

W/ m

2K

Description:

The apparatus consists of a brass tube fitted in a rectangular duct in a vertical

fashion. The duct is open at the top and bottom and forms an enclosure and serves the

purpose of undisturbed surrounding. One side of it is made up of glass/acrylic for

visualization. A heating element is kept in the vertical tube, which heats the tube surface.

The heat is lost from the tube to the surrounding air by natural convection. Digital

temperature indicator measures the temperature at the different points with the help of seven

temperature sensors. The heat input to the heater is measured by digital ammeter and digital

voltmeter and can be varied by a dimmerstat.


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1. Clean the apparatus and make it free from dust, first.

2. Ensure that all On/Off switches given on the panel are at OFF position.

3. Ensure that variac knob is at ZERO position, given on the panel.

4. Now switch on the main power supply (220 V AC, 50 Hz).

5. Switch on the panel with the help of mains On/Off switch given on the panel.

6. Fix the power input to the heater with the help of variac, voltmeter and ammeter

provided.

7. After 30 minutes record the temperature of test section at various points in each 5

minutes interval.8. If temperatures readings are same for three times, assume that steady state is

achieved.

9. Record the final temperatures.

Specification:

Dia of the tube = 35 mm

Length of the tube = 500 mm

Size of duct = 25 25 90 cm

Temperature Sensors = RTD PT-100 type

No. of RTD Temperature Sensors = 8 Nos.

Digital Voltmeter = 0 to 250 V

Digital Ammeter = 0 to 2.5 Amps

Dimmerstat = 2 Amps/220 V

Temperature Indicator = Digital temperature indicator 0 to

200oC with multi channel switch.


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Formulae:

1. The heat transfer coefficient,

h =( )

a

s a

Q

A T T W/m

2.K

Where

Qa = heat transfer rate = VI(W)

A = Area of the heat transferring surface = d L (m)

1 2 3 4 5 6 7

7s

T T T T T T T T

Ta = ambient temperature in duct C = T8

Exercises:

1. Find out the heat transfer co-efficient of vertical cylinder in natural convection


1. Use the stabilize A.C. single phase supply only.2. Never switch on mains power supply before ensuring that all the ON/OFF switches




5. Never run the apparatus if power supply is less than 180 V and above than 240 V.






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Experiment 5

DROPWISE AND FILMWISE CONDENSATION

Objective:

To find the heat transfer coefficient for dropwise condensation and filmwise

condensation process.

Theory:

Steam may condense on to a surface in two distinct modes, known as Filmwise &

Dropwise. For the same temperature difference between the steam & the surface,

Dropwise condensation is much more effective than Filmwise & for this reason the former is

desirable although in practical plants it rarely occurs for prolonged periods.

Film Condensation:

Unless specially treated, most materials are wettable & as condensation occurs a film

condensate spreads over the surface. The thickness of the film depends upon a numbers of

factors, e.g. the rate of condensation, the viscosity of the condensate and whether the surfaceis vertical or horizontal, etc.

Fresh vapor condenses on to the outside of the film & heat is transferred by conduction

through the film to the metal surface beneath. As the film thickness it flows downward &

drips from the low points leaving the film intact & at an equilibrium thickness.

The film of liquid is a barrier to the transfer of heat and its resistance accounts for

most of the difference between the effectiveness of Filmwise and drops wise condensation.

Dropwise Condensation:

By specially treating the condensing surface the contact angle can be changed and

the surface becomes non-wettable. As the steam condenses, a large number of generally

spherical beads cover the surface. As condensation proceeds, the beads become larger,

coalesce, and then strike downwards over the surface. The moving bead gathers all the


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static beads along its downward in its trail. The bare surface offers very little resistance to

the transfer of heat and very high heat fluxes are therefore possible.

Unfortunately, due to the nature of the material used in the construction of

condensing heat exchangers, Filmwise condensation is normal. (Although many bare metal

surfaces are non - wettable this is not true of the oxide film which quickly covers the bare

material)

Description:

The equipment consists of a metallic container in which steam generation takes

place. The lower portion houses suitable electric heater for steam generation. A special

arrangement is provided for the container for filling the water. The glass cylinder housestwo water cooled copper condensers, one of which is chromium plated to promote Dropwise

condensation and the other is in its natural state to give Filmwise condensation. A

connection for pressure gauge is provided. Separate connections of two condensers for

passing water are provided. One Rota meter with appropriate piping can be used for

measuring water flow rate in one of the condensers under test.

A digital temperature indicator provided has multipoint connections, which measures

temperatures of steam, two condensers, water inlet & outlet temperature of condenser water

flows.


1. Fill water in steam generator by opening the valve.

2. Start water flow through one of the condensers, which is to be tested and note down

water flow rate in Rota meter. Ensure that during measurement, water is flowing only

through the condenser under test and second valve is closed.

3. Connect supply socket to mains and switch ON the heater switch.

4. Slowly steam generation will start in the steam generator of the unit and the steam rises

to test section, gets condensed on the tubes and falls down in the cylinder.

5. Depending upon type of condenser under test Dropwise or Filmwise can be visualized.


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6. If the water flow rate is low then steam pressure in the chamber will rise and pressure

gauge will read the pressure. If the water flow rate is matched then condensation will

occur at more or less atmospheric pressure or up to 1 kg pressure.

7. Observations like temperatures, water flow rates, pressure are noted down in the

observations table at the end of each set.

Specification:

Condensers = One gold plated for Dropwise condensation & one

natural finish for Filmwise condensation otherwise identical

in construction.

Dimensions = 20 mm outer dia. 160 mm length, Fabricated from copper with

reverse flow in concentric tubes. Fitted with temperature

sensor for surface temperature measurement.

Main Unit = M.S. Fabricated construction comprising test section & steam

generation section. Test section provided with glass cylinder

for visualization of the process.

Heating Elements = Suitable water heater.

Instrumentation = 1) Temperature Indicator: Digital 0-199.9

o

C & least count0.1

oC with multi-channel switch.

2) Temperature Sensors: RTD PT-100 Type.

3) Rota meter: for measuring water flow rate.

4) Pressure Gauge: Dial type 0 - 2 Kg/cm2

Formulae:

1. Heat losses from steams s

Q M

2. Heat taken by cold water w w P

Q M C T

3. Average hear transfer 2

QwQsQ


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4. Inside heat transfer coefficienti

i

Qh

T

5. Outside heat transfer coefficient oo

QhT

6. Experimental overall heat transfer coefficient 1 1 1i

EX i o o

D

U h D h

7. Reynolds Number 1 1

4Re w

d

i

m

D

8. Prandtl Number Pr

CP

K

9. Nusselt Number Nu1 = 0.023 (Red)0.8

(Pr)0.4

10. Inside heat transfer coefficient Km/WL

KNuh

21i

11. Out side heat transfer coefficient 25.0

WS

3

2

2

2o

L)TT(

gk943.0h

12. Theoretical overall heat transfer coefficient 1 1 1i

TH i o o

DU h D h

Nomenclature:

Di = Inner Dia of condenser, m

hi = Inside Heat Transfer Coefficient, W/m2K

TS = Temperature of steam, C.

TW = Temperature of condenser wall, CMs = Rate of steam condensation, Kg/s

Mw = Cold water flow rate, Kg/s

Cp = Specific heat of water, kJ/kgK

g = Acceleration due to gravity, m/s2

L = Length of condenser, m


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= Density of water, kg/m3

= Kinematics Viscosity, m2/sec.

k = Thermal conductivity, W/mK

Pr = Prandtl number

T1 = Surface Temperature of Plated Condenser,oC

T2 = Surface Temperature of Plain Condenser,oC

T3 = Temperature of steam in column,oC

T4 = Water inlet temperature,oC

T5 = Water outlet temperature,oC

Data:

Outer diameter of heat transfer surface,Do = 20 mm

Inner diameter of heat transfer surface,Di = 17 mm

Length of heat transfer surface,L = 160 mm

Inside heat transfer area,Ai = 0.008549 m2

Outside heat transfer area,Ao = 0.010057 m2

Calculation:

1. Heat transfer coefficient at inner surface

Properties of water at bulk mean temperature of water i.e. (T5 +T6)/2 Where T5 and T6 are

water inlet and outlet temperatures.

Following properties are required. :

CP = Specific heat of water, kJ/kgK

1 = Density of water kg/m3

1 = Kinematics Viscosity m2/sec

= Viscosity of water, N.s/m2

k1 = Thermal conductivity, W /m K

Now calculate

Reynoldss number 11i

wd

D

m4Re


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Prandtl Number K

CP Pr

Nusselt Number Nul = 0.023 (Red)0.8

(Pr)0.4

Calculated heat transfer coefficient at inside surface2

1 W/m Ki

Nu Khcal

L

Experimental heat transfer coefficient at inside surface hiexp =)65( TTAi

mS

2W/m K

2. Heat transfer coefficient at outer surface

Calculated value

Now calculate heat transfer coefficient on outer surface of the condenser (ho). For this

properties of water are taken at bulk mean temperature of condensate i.e.

2

43 TT C = Tc C

Properties needed at Tc C are

i) 2 = Density of water, Kg/m3

ii) K 2 = Thermal Conductivity, W/ m K

iii) = Viscosity of condensate, N.s/m2

iv) = Heat of evaporation kJ/Kg. (2257 kJ/kg)

0.252 3

2 2

3 4

0.943( )

o

gkh cal

T T L

2

W/m K

From these values overall Heat Transfer coefficient (U) can be calculated.

1 1 1

i

i o o

D

Ucal hcal D h

2

1

W/m K

and

Experimental heat transfer coefficient at outer surface

3 4

3 4

Heat Flux ( - )

Condensation flux for a length L ( 3 - 4)/

exp( - )

o

s

o

o o

h T T

h T T

Q h AT

Q mh

A T A T T


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Observed heat transfer coefficient = expo

h 2

W/m K

Condensation Flux =exp( )

o Sh T T

1 1 1

exp exp expi

i o o

D

U h D h

Compare the observed heat transfer coefficient with that calculated.

Exercises:

1. Calculate transfer coefficient at inner surface.

2. Calculate transfer coefficient at outer surface.

3. Find out the overall heat transfer coefficient

4. Same procedure can be repeated for other condenser. Except for some exceptional

cases overall heat transfer coefficient for Dropwise condensation will be higher than

that of Filmwise condensation. Results may vary from theory in some degree due to

unavoidable heat losses.

Precautions and Maintenance instructions:






5. Never run the apparatus if power supply is less than 180 volts and above than 240

volts.


7. Do not start heater supply unless water is filled in the test unit.





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Experiment 6

HEAT TRANSFER FROM A PIN FIN

Objective:

To study the temperature distribution along the length of a pin fin under free and

forced convection heat transfer and find the fin efficiency.

Theory:

It is obvious that a fin surface stick out from primary heat transfer surface. The

temperature difference with surrounding fluid will steadily diminish as one moves out along

the fin. The design of the fins therefore requires knowledge of the temperature distribution

in the fin. The main object of this experimental set up is to study the temperature

distribution in a simple pin fin.

Fin efficiency =tanhwith fin

without fin

C

f

C

mLq

q mL

The temperature profile within a pin fin is given by:

0

[ ] [cosh ( - ) sinh ( - ) ][ ] [cosh sinh ]

f

b f

T T m L x H m L x

T T mL H mL

Where Tf is the free stream temperature of air; Tb is the temperature of fin at its base;

Tis the temperature within the fin at any x;L is the length of the fin, D is the fin diameter

and m is the fin parameter.

Fin parameter m = /b

h P k A

The volume coefficient of expansion, 1/ 273.15mfT , 1/K

Velocity of air = V= Q / cross-sectional area of duct

2

4

24

1

o oC d g H

Q

m

3/s (at temperature = Tf)


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where o

p

d

d

Velocity of air at Tmf may be calculated from: V = V[Tmf+ 273.15] / [Tf + 273.15]

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 blower and the air flows past the

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

heater. RTD PT-100 type temperature sensors measure temperatures at five points along the

length of the fin. An orifice meter, fitted on the delivery side of the blower, measures the

flow rate of air.


Natural Convection:

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

dimmerstat to say 80 volts (Increase slowly from 0 onwards).

Note down the temperature sensors readings no.1 to 5.

2. When steady state is reached, record the final readings of temperature sensor no.1 to

5 and also the ambient temperature reading temperature sensor No 6.

3. Repeat the same experiment with voltage. = 100 volts and 120 volts.

Forced Convection:

1. Start heating the fin by switching on the heater and adjust dimmerstat voltage equal

to 100 volts.

2. Start the blower and adjust the difference of level in the manometer H = cm with the

help of fly valve provided on the pipe.

3. Note down the Temperature Sensor readings (1) to (5) at a time interval of 5

minutes.

4. When the steady state is reached, record the final readings (1) to (5) and also record

the ambient temperature readings by (6)


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5. Repeat the same experiment with another H = cm etc.

Specification:

Duct size = 150 mm 100 mm 1000 mmDiameter of the fin (D) = 12.7 mm

Length of the fin (L) = 125 mm

Diameter of the Orifice (do) = 39 mm

Inner diameter of the delivery pipe (dP) = 52 mm

Coefficient of discharge (Orifice meter) Co = 0.64

Temperature Indicator = 0-200oC, RTD PT-100 type

RTD PT-100 type Sensors = 6 Nos.

Temperature Sensor no.6 reads ambient temperature in the inside of the duct.

Thermal conductivity of fin material (Brass) = 110 W/ m K

Centrifugal blower with Single-phase motor.

Dimmerstat for heat input control 230 V, 2 Amps.

Heater suitable for mounting at the fin end outside the duct.

Voltmeter 0- 250 V.

Ammeter 0- 2 A.

Free Convection:

Mean temperature of the fin , Tm = 1 2 3 4 5( ) /5T T T T T

Tmf (Mean film temperature) = ( ) / 2m fT T

The volume coefficient of expansion, = 1/( 273.15)mf

T

Grashof number, Gr =3 2( ) /g D T

Using the correlation for free convection:

Nusselt number,Nu = 1/ 40.53( Pr) /air

Gr h D k

Free convective heat transfer coefficient, h = /air

Nu k D

Fin parameter, m = /f

h P k A

Perimeter,P = D


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Cross-sectional area of fin,A = D2 / 4

Fin diameter,D = 12.7 10-3 m

Fin length,L = 125 10-3 m

Fin efficiency,tanh

C

f

C

mL

mL

Fin effectiveness =with fin

tanhwithout fin

f

c

c

k PqmL

q hA

Corrective length,LC = ( / 4)L D

Parameter,H = /f

h k m

Theoretical temperature profile within the fin =

0

[ ] [cosh ( - ) sinh ( - ) ][ ] [cosh sinh ]

f

b f

T T m L x H m L x

T T mL H mL

Taking base temperature, Tb = T1

Forced convection:

Orifice coefficient, Co = 0.64

Volumetric flow rate of air, Q =

2

4

24

1

o oC d g H

H = [ ( / -1)] /100w a

h

Velocity of air, V = Q / a (at ambient fluid temp.)

Velocity of air at mean film temperature,1

( 273.15 ) /( +273.15)mf f

V V T T

Reynolds number,Re = 1 /D V Using the correlation for force convection:

Nusselt Number,Nu = 0.615 (Re )0.466

= / airh D k

Heat transfer coefficient, h = /airu k D


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Fin parameter, m = /f

hC k A

Nomenclature:

Kf = thermal conductivity of brass fin, W/ m K

C = perimeter, m

Tm = fin mean temperature,oC

Tf = surrounding fluid temperature,oC

x = distance of the sensor at base of the fin, cm

g = acceleration due to gravity, m/s2

D = fin diameter, m

Gr = Grashoffs number

Pr = Prandtl number

Nu = Nusselt number

Kair = air conductivity at mean temperature, W/ m Kh = heat transfer coefficient, W/ m

2K

m = fin parameter, m

A = x-sectional area of fin, m2

L = fin length, m

f = fin efficiency

= the density of air, kg/m3

= the dynamic viscosity of air, kg/m.s

= the kinematic viscosity of air, m2/s

Cp = the specific heat of air, kJ/kg.K

k = the thermal conductivity of air, W/ m.K

Q = volumetric flow rate of air through the duct, m3/s

Co = the orifice coefficient = 0.64

D = the orifice diameter, m

w = the density of water (manometer fluid = 1000 kg/m3)

H = the orifice manometer reading, m

V = velocity of air at Tmf, m/s

Tmf = fluid mean temperature,oC


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Exercises:

1. Find the fin efficiency

2. Calculate the fin effectiveness

3. Plot the temperature profile within the fin T Vsx






provided.



volts.






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Experiment 7

THERMAL CONDUCTIVITY OF LIQUIDS

Objective:

To determine the thermal conductivity of a liquid

Theory:

For thermal conductivity of liquids using Fouriers law, the heat flow through the

liquid from hot fluid to cold fluid is the heat transfer through conductive fluid medium.

Fouriers equation:

2 1T TQ kAX

Fouriers law for the case of liquid

At steady state, the average face temperatures are recorded (Th and Tc) along with

the rate of heat transfer (Q). Knowing, the heat transfer area (Ah) and the thickness of the

sample (X) across which the heat transfer takes place, the thermal conductivity of the

sample can be calculated using Fouriers Law of heat conduction.

X

TTkA

X

TkAQ Chhh

heat transfer area = Ah (area to direction of heat flow)

Description:

The apparatus is based on well-established Guarded Hot Plate method. It is a

steady state absolute method suitable for materials, which can be fixed between two parallel

plates and can also be extended to liquids that fill the gap between the plates.

The essential components of the set-up are the hot plate, the cold plate, and heater to

heat the hot plate, cold water supply for the cold plate, RTD PT-100 Sensors and the liquid

specimen holder. In the set-up, a unidirectional heat flow takes plate across the liquid whose


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two faces are maintained at different temperatures by the hot plate on one end and by the

cold plate at the other end.

A heater heats hot plate and voltage to the heater is varied with the help of Variac to

conduct the experiment on different voltages as well as different heat inputs. Temperatures

are measured by RTD PT-100 sensors attached at three different places on the hot plate as

well as on the cold plate. These sensors are provided on the inner surface facing the liquid

sample. An average of these sensor readings are used as Th and Tc at steady state condition.

Heat is supplied by an electric heater for which, we have to record the voltmeter

reading (V) and ammeter reading (A) after attaining the steady state condition. The

temperature of the cold surface is maintained by circulating cold water at high velocity. The

gap between hot plate and cold plate forms the liquid cell, in which liquid sample is filled.

The depth of the liquid in the direction of flow must be small to ensure the absence

of convection currents and a liquid sample of high viscosity and density shall further ensure

the absence of convection and the heat transfer can be safely assumed to take place by

conduction alone.


Fill the liquid cell with the sample liquid (glycerol) through the inlet port, keeping theapparatus tilted towards upper side so that there is complete removal of air through the outlet

port. Liquid filling should be continued till there is complete removal of air and also liquid

glycerol comes out of the outlet port. Close the outlet port followed by inlet port.

1. Allow cold water to flow through the cold-water inlet.

2. Start the electric heater to heat hot plate. Adjust the voltage of hot plate heater in the

range of 10 to 50 volts.

3. Adjust the cold-water flow rate such that there is no appreciable change the outlet

temperature of cold water (there should be minimum change).

4. Go on recording the thermocouple readings on hot side as well as on cold side, and

once steady state is achieved (may be after 30-60 min); (steady state is reached when

there no appreciable change in the thermocouple readings, 0.1oC), record the three

thermocouple readings (Th1,Th2,Th3 i.e. T1, T2 T3 on Temperature Indicator) on the hot


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side and three thermocouple readings ( Tc1 , Tc2, Tc3 i.e. T4, T5, T6 on Temperature

Indicator) on the cold side along with the voltmeter (V) and ammeter (A) readings.

5. Stop the electric supply to the heater, and continue with the supply of cold water till

there is decrease in temperature of hot plate (may be for another 30-40 min).

6. Open the liquid outlet valve slightly in the downward tilt position and drain the

sample liquid in a receiver, keeping liquid inlet port open.

Specification:

1. Hot Plate

Material = Copper

Diameter = 160 mm

2. Cold Plate

Material = Copper

Diameter = 160 mm

3. Sample Liquid depth = 20 mm

4. Temp. Sensors = RTD PT-100 type.

Type = RTD PT-100 type

Quantity = 6 Nos.No. 1 to No. 3 mounted on hot plate.

No. 4 to No. 6 mounted on cold plate.

5. Digital Temperature indicator

Range = 0C to 199.9C

Least Count = 0.1oC

6. Variac = 2 Amp, 230VAC

7. Digital Voltmeter = 0 to 250 Volts

8. Digital Ammeter = 0 to 2.5 Amp.

9. Heater = Nichrome heater 440 Watt


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Formulae:

1. Heat input Q V I

2. Thermal conductivity of liquid,

( )

h c

XK Q

T T

Hot face average temperature, Th = (Th1 + Th2 +Th3) / 3

Cold face temperature, Tc = (Tc1 + Tc2 + Tc3) / 3

Temperature difference, T = (Th - Tc)

Nomenclature:

Q = Heat supplied by heater, W

A = Heat transfer area, m2

Th = Hot face average temperature,OC

Tc = Cold face average temperature,OC

T = Temperature difference,OC

K = Thermal conductivity of liquid, w/mK

X = Thickness of liquid, m

Exercises:

1. Determine the thermal conductivity of a liquid


1. Use the stabilize A.C. single phase supply only.






volts.



8. Testing liquid should be fully filled.


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Experiment 8

THERMAL CONDUCTIVITY OF INSULATIING POWDER

Objective:

To determine thermal conductivity of insulating powder

Theory:

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

formed by the insulating powdered layer packed between two thin copper spheres.

Let ri = radius of inner sphere, meter

ro = radius of outer sphere, meter

Ti = average temperature of the inner surface, C

To = average temperature of the outer surface, C

Where, 1 2 3 4

4i

T T T T T

and 5 6 7 8 9 100

6

T T T T T T T

From the experimental values of Q, Ti and To, the unknown thermal conductivity kcan be

determined as:

4o i

o i i o

Q r rk

r r T T

Description:

The apparatus consists of two thin walled concentric spheres of copper of different

size. The small inner copper sphere houses the heating coil. The insulating Powder (Plaster

of Paris) is packed between the two spheres. The power given to the heating coil is

measured by voltmeter and ammeter and can be varied by using dimmerstat. There are ten

(T1 to T10) thermocouples embedded on the copper spheres, T1 to T4 (4 nos.) are embedded

on the inner sphere and rest T5 to T10 (6 nos.) on the outer sphere. Thermal conductivity of

insulating powder can be found out by taking the temperature reading of these


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thermocouples. Assume that insulating powder is an isotropic material and the value of

thermal conductivity to be constant. The apparatus assumes one-dimensional radial heat

conduction across the powder and thermal conductivity can be determined.


1. Switch on the main power supply 220 AC single phase, 50 Hz.

2. Increase slowly the input to heater by the dimmerstat starting from zero volt position.

3. Adjust input equal to any value between 20 to 60 Watt maximum by voltmeter and

ammeter.

4. Thermocouple readings are taken at frequent intervals (say once in 10 minutes) till

consecutive readings are same indicating that steady state has been reached.

5. Note down the readings in the observation table.

Specification:

Radius of the inner copper sphere, ri = 50 mm

Radius of the outer copper sphere, ro = 100 mm

Voltmeter = 0-300 V

Ammeter = 0-2 ATemperature Indicator = 0-300 C.

Dimmerstat = 0-2A, 0-230 V

Heater coil-strip heating element sandwiched between mica sheets

Thermocouples of numbers T1 to T4 are embedded on the inner sphere to measure Ti

Thermocouples of numbers T5 to T10 are embedded on the outer sphere to measure To

Insulating powder-plaster of paris commercially available powder and packed between the

two spheres.

Formulae:

1. Heat input, Q V I

2. Thermal conductivity of insulating power:


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(W/m.K)4

o i

o i i o

Q r rk

r r T T


the input is not adjusted till the satisfactory steady state condition reached.

Nomenclature:

ri = Inner Radius, meters

ro = Outer Radius, meters

Ti = Inside surface temperature, C

To = Outside surface temperature, C

Q = Heat Input.

V = Voltmeter reading.

I = Ammeter reading

Exercises:

1. Determine the thermal conductivity of an insulating powder






provided.



volts.






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Experiment 9

HEAT TRANSFER IN FORCED CONVECTION

Objective:

To find surface heat transfer coefficient between a heated pipe and air flowing

through it by forced convection, for different air flow rates and heat flow rates.

Theory:

Air flowing in to the heated pipe with very high velocity the heat transfer rate

increases. The heat is taken by the cold air from the heat source and rises its temperature.

Thus, for the tube the total energy added can be expressed in terms of a bulk-temperature

difference by

2 1( )

P b bq mC T T

Bulk temperature difference in terms of heat transfer coefficient

q hA T

A traditional expression for calculation of heat transfer in fully developed turbulent flow in

smooth tubes is that recommended by Dittus and Boelter

0.8

0.023Re Pr n

d dNu

if n = 0.4 for heatingof thefluid

0.3 for coolingof thefluid

Description:

The apparatus consists of blower unit fitted with the test pipe. The test section is

surrounding by nichrome heater. Four Temperature Sensors are embedded on the test

section and two temperature sensors are placed in the air stream at the entrance and exit of

the test section to measure the air temperature. Test Pipe is connected to the delivery side of

the blower along with the Orifice to measure flow of air through the pipe. Input to the

heater is given through a dimmerstat and measured by meters. It is to be noted that only a


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part of the total heat supplied is utilized in heating the air. A temperature indicator is

provided to measure temperature of pipe wall in the test section. Airflow is measured with

the help of Orifice meter and the water manometer fitted on the board.

Temperature sensors:

T1 = Air inlet temp.

T2, T3, T4, T5 = Surface temp. of test section

T6 = Air outlet temp.


1. Clean the apparatus and make it free from Dust.

2. Put Manometer Fluid (Water) in Manometer connected to Orificemeter.

3. Ensure that all On/Off Switches given on the Panel are at OFF position.

4. Ensure that Variac Knob is at ZERO position, given on the panel.

5. Now switch on the Main Power Supply (220 V AC, 50 Hz).

6. Switch on the Panel with the help of Mains On/Off Switch given on the Panel.

7. Fix the Power Input to the Heater with the help of Variac, Voltmeter and Ammeter

provided.

8. Switch on Blower by operating Rotary Switch given on the Panel.9. Adjust Air Flow Rate with the help of Air Flow Control Valve given in the Air

Line.

10. After 30 Minutes record the temperature of Test Section at various points in each 5

Minutes interval.

11. If Temperatures readings are same for three times, assume that steady state is

achieved.

12. Record the final temperatures.

13. Record manometer reading.


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Formulae:

1. exp.

( )

a

s a

Qh

A T T

2. 1W

a

H H

3.4

2

oo

1

Hg2d4

C

Q

Where

dp

do

4. Qa = m CpT

5. m = Q a

6. A = Di L

7. Ta =1 6

2

T T

8. Ts =2 3 4 5

4

T T T T

Nomenclature:

m = mass flow rate of air, Kg/ sec.

Cp = Specific heat of air, J/ Kg C.T = Temp. rise in air C. (T6 - T1)

a = Density of air, kg/ m3

w = Density of water, kg/m3

Q = Vol. flow rate, m3/ sec.

Qa = Heat carried away by air, W

hexp. = experimental value of heat transfer coefficient, W/ m2 0

C

Co = Coefficient of dischargeH = Difference of water level in manometer, m.

d0 = Diameter of Orifice, m

A = Test section area, m2

Ta = Average temperature of air, C

Ts = Average surface temperature, C


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L = Length of test section, m

Di = I.D. of Test section, m

Exercises:

1. Calculate experimental value of heat transfer coefficient.

2. Calculate theoretical value of heat transfer coefficient.

3. Write your comments on above calculations.


1. Use the stabilize A.C. Single phase supply only.






volts.6. Operate selector switch of temperature indicator gently.





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Experiment 10

HEAT PUMP TRAINER

Objective:

To determine the coefficient of performance (COP) of heat pump trainer

Theory:

Mechanical Heat Pump is defined as an assembly of different parts of the system

used to produce a specified condition of air within a required space or building. An ideal

system should maintain correct temperature, humidity, air-purity, air-movement and noise

level. Always, it is not possible to maintain all the above factors mentioned and a

compromise should be made to make the system economic.

The main function of the heat pump is to maintain body at a temperature that is

higher than the atmosphere. Though the body may be insulated some heat, say QHis flowing

out of the body to the atmosphere. Such heat QH is supplied to the body so that its

temperature is maintained. For this work W is supplied which removes heat QL from

atmosphere which is at temperature TL and supplies heat QHto the body.

QL + W = QL

Here the heat pump maintains the body at a temperature THwhich is higher than

atmospheric temperature TL. For this it does work W.

Description:

The compressor is used for pumping the refrigerant through the system. The

condenser is the forced water-cooled type for which heat exchanger has been provided.

Capillary Tube is provided as an expansion device for evaporator. A temperature indicator

with multi-point selection switch has been provided to get the various temperatures viz.

T1 = Refrigerant Temperature at Suction,0C


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T2 = Refrigerant Temperature at Discharge,0C

T3 = Refrigerant Temperature before Expansion,0C

T4 = Refrigerant Temperature after Expansion,0C

T5 = Temperature of Water in evaporator tank,0C

T6 = Temperature of Water out evaporator tank,0C

T7 = Temperature of Water inlet to Condenser,0C

T8 = Temperature of Water outlet of Condenser,0C

The selection of any of the temperature can be made by rotating the selection switch

to the respective channel. We have provided four pressure gauges for indicating R-134(a)

pressures at compressor suction P1, compressor discharge P2, after condenser P3, after

Capillary Tube P4. Energy-meter is provided for measuring power input to the compressor.


1. Switch on mains supply.

2. Switch "ON" the condenser motor and then switch "ON" the compressor.

3. Please do not start the compressor when condenser motor is "OFF". First switch "ON"

the condenser motor and then switch "ON" the compressor.

4. By using selector switch on temperature indicator, note the temperature T1, T2, T3, T4, T5,

T6, T7 and T8 in the observation table.

5. Note the pressures of R-134(a) gas in the circuit by noting pressures P1, P2, P3, and P4 in

the observation table.

6. Note down the energy-meter reading (i.e., time taken in seconds for the wheel to

complete one revolution)

7. Repeat the above procedure to get different sets of readings every 10 minutes till you get

fairly constant temperatures of the consecutive readings. Confirm this by taking one

more set of readings

8. Calculate the COP as per the procedure of calculations given below.

9. Switch off all the switches after you complete the experiment


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Formulae:

1. COP (Carnot refri) 1

2 1

T

T T

COP (Carnot heat pump) = COP (refri) + 1

Convert the pressure in psi to pressure in Bar (Absolute)

14.8 psi 1 atm

Absolute pressure 1 1 /14.8 1P P

By taking1

P from the chart find the corresponding value of1

T

1

T Saturation temperature at suction pressure

Refer table (Saturated properties of R-134a liquid and vapour)

Similarly find2

P and2

T

2

T Saturation temperature at condenser pressure

2. C.O.P. (Theoretical) 2 3

2 1

h h

h h

Where

h1 = enthalpy for gas at temperature T1

h2 = enthalpy for gas at temperature T2

h3= enthalpy for liquid of at temperature T3

3. C.O.P (actual)Desired output

Required input

C.O.P (actual)Heat transferred to water

Power consumed by the compressor

power consumed by the compressor

pmc T

t

Where

m = mass flow rate of water passing through the condenser


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2 lph Density of water secm kg/sec

3600 1000

F t

cp = specific heat of water = 4.18 kJ/kg.K

T = temperature difference between T7 and T8 in K.

F1 = refrigerant flow, LPH

F2 = water flow through the condenser, LPH

F3 = water flow through the evaporator, LPH

We can calculate power consumed by the compressor as follows:

Power Consumed (kW) 1

3600 no. of blinks per second3200

Exercises:

1. Determine the coefficient of performance (COP) of heat pump trainer


1. Before operating the system, check the level of water inside the water tank.

2. Do not change settings of LP-HP cut off Valve.

3. Do not touch the charging valve. If this valve gets opened slightly, all refrigerant

will escape leading to non-performance of the instrument.

4. Once the experiment is over, remove water from the water tank.

5. Please do not start the compressor when condenser motor is "OFF". First switch

"ON" the condenser motor and then switch "ON" the compressor.


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Experiment 11

TO DETERMINE THE COEFFICIENT OF PERFORMANCE (COP) OF

A VAPOUR COMPRESSOR TRAINER

Objective:

To determine the coefficient of performance (COP) of refrigeration trainer

Theory:

In general, refrigeration is defined as any process of heat removal. More specifically,

refrigeration is defined as the branch of science that deals with the process of reducing and

maintaining the temperature of a space or material below the temperature of the

surroundings. The system maintained at the lower temperature is known as refrigerated

system while the equipment used to maintain this lower temperature is known as

refrigerating system.

In accordance with the Clausiuss statement of second law of thermodynamics, heat

does not flow from a low temperature region to high temperature region without the aid of

external energy. This transfer of heat against a reverse temperature gradient can be

accomplished if mechanical energy is supplied to the machine. A machine which maintains

a space at a lower temperature than the surrounding is known as a refrigerator and the

process is known as refrigeration. Refrigeration therefore implies the cooling or removal of

heat from a system. Such cooling may be obtained by any one of the following principles.

i. By chemical means, in which chemical reaction is carried out which absorbsheat for its completion. The heat required for the purpose is taken from the substance

or space to be cooled.

ii. By bringing the substance to be cooled directly or indirectly in contact with

some cooling medium such as chilled water or ice.


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iii. By using mechanical or heat energy to operate a heat pump by which heat

may be abstracted from a low temperature region and rejected to high

temperature region.

Description:

The refrigeration trainer consists of compressor, condenser, capillary, heater and

water container. The compressor is used for pumping the refrigerant through the system. The

condenser is the forced air-cooled type for which condenser fan and motor has been

provided. Capillary is provided as an expansion device for evaporator. Heater is provided to

change the load on the system. A temperature indicator with multi-point selection switch has

been provided to get the various temperatures viz.

T1 Refrigerant temperature at suction

T2 Refrigerant temperature at discharge

T3 Refrigerant temperature before expansion

T4 Refrigerant temperature after expansion

T5 Temperature of water

The selection of any of the temperature can be made by rotating the selection switch to the

respective channel. Four pressure gauges are provided for indicating R-134a pressures at

compressor suction P1, compressor discharge P2, after condenser P3, after thermostatic

expansionP4.


1. Switch on Mains Supply. Switch on the trainer.

2. By using selector switch on temperature indicator, note the temperature T1, T2, T3, T4 and

T5 in the observation table.

3. Note the pressures of R-134a gas in the circuit by noting pressuresP1, P2, P3, P4 in the

observation table.


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4. Repeat the above procedure to get different sets of readings for different loads every 10

minutes till you get fairly constant temperatures of the consecutive readings. Confirm

this by taking one more set of readings


6. Switch off all the switches after you complete the experiment.

7. Remove water from the water tank.

Formulae:

1. COP (Reversed Carnot) 1

2 1

T

T T

Convert the pressure in psi to pressure in Bar (Absolute) 14.8 psi 1 atm

Absolute pressure 1 1 /14.8 1P P

By taking1

P from the chart find the corresponding value of1

T

1T Saturation temperature at suction pressure

Refer table (Saturated properties of R-134a liquid and vapour)

Similarly find2

P and2

T

2T

Saturation temperature at condenser pressure

2. C.O.P (Theoretical) 1 4

2 1

h h

h h

Where,

h1 = enthalpy (for gas) at temperature T1

h2 = enthalpy (for gas) at temperature T2

h4 = enthalpy (for liquid) at temperature T4

3. C.O.P (Actual)desired output

required input

heat transferred by wate



pmc T

t


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Where

m = mass of water

cp = specific heat of water = 4.18 KJ/Kg.K

T = temperature difference in T5 over a period of time t (sec)

We can calculate power consumed by the compressor as follows:

Power Consumed (Kw) 1

3600 no. of blinks per second3200

Exercises:

1. Determine the coefficient of performance (COP) of refrigeration trainer


1. Before operating the system, check the level of water inside the Water Tank (i.e. the

Refrigerated Space). Water should be filled up to the marked level.

2. Do not start the compressor when condenser motor is "OFF". First switch "ON" the

condenser motor and then switch "ON" the compressor.

3. Do not change settings of LP-HP cut off Valve.

4. Do not run agitator motor for a period more than 15 min continuously. Turn it off for

a few minutes and then start it again. This allows proper cooling of the agitator

motor.

5. Do not touch the charging valve. If this valve is opened slightly, the entire

refrigerant will leak leading to non-performance of the instrument.

6. Once the experiment is over, remove water from the water tank so as to prevent

rusting of any parts inside the test chamber.


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Experiment 12

VAPOR ABSORPTION REFRIGERATION TRAINER

Objective:

To determine the coefficient of performance (COP) of vapor absorption refrigeration trainer

Theory:

The function of the compressor in the vapor-compression system is to continuously withdraw

the refrigerant vapor from the evaporator and to raise its temperature and pressure so that the heat

absorbed in the evaporator, along with the work of compression may be rejected in the condenser.

In the vapor-absorption system the function of the compressor is accomplished in a three

step process by the use of the absorber, pump and generator as follows

(i) Absorber: Absorption of the refrigerant vapor by its weak or poor solution in a suitable

absorbent or adsorbent, forming a strong or rich solution.

(ii) Pump: Pumping of the rich solution raising its pressure to the condenser pressure.

(iii) Generator: Distillation of the vapor from the rich solution leaving the poor solution for

recycling.

Description:

The simple vapor absorption trainer consists of a condenser as an expansion device and an

evaporator as in the vapor-compression system. In addition, absorber, pump, generator and a

pressure reducing valve to replace the compressor.

The flow of fluids in the system is described as follows

1. Vertical boiler in which an aqua solution of ammonia can range itself from distilled water at

the bottom of the boiler to strong ammonia vapor at the surface of the liquid.

2. A water separator which is provided to remove water vapor so that they should not enter the

condenser, get condensed there and pass on to evaporator where chocking might occur due to

its freezing. The water vapor is formed in the boiler as some of the water may evaporate on


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application of heat to the boiler. The separator is jacketed with liquid ammonia at a pressure

of about 14 bar gauge for which the saturation temperature is about 40C.

3. The dehydrated ammonia gas gets condensed to liquid in the condenser and gravitates to U

tube which acts as seal for a gas to enter the evaporator, or any gas passing from evaporator to

the condenser.

4. In the evaporator, the ammonia liquid comes across an atmosphere of hydrogen at about 12

bar gauge. The plant is charged to a pressure of about 14 bar. Hence due to Daltons law of

partial pressure, the pressure of ammonia gas should fall to about 2 bar gauge and the

saturation temperature corresponding to about 2 bar is about 10C. The temperature

surrounding the evaporator is much higher than this. Thus ammonia evaporates and produces

the refrigerating effect i.e. absorbs the latent heat of vaporization at 2 bar gauge and about -

10C from the space to be refrigerated.

5. In order to ensure continuous action, hydrogen gas has to be removed from ammonia vapor.

This is done in the absorber where a descending spray of very dilute ammonia liquid meets

the ascending mixture of ammonia vapor and hydrogen. Ammonia vapor is readily absorbed

with evaluation of heat so that absorber has to be water jacketed or air cooled, otherwise

evaporation may take place in this unit and the absorption may cease.

6. Heat exchanger: liquid heat exchanger is placed in between absorber and the generator. This

week liquid gets cooled and strong liquid gets heated. Thus heat is economized and better

thermal efficiency obtained. This heat exchanger is counter-flow type. The strong solution

from the absorber is preheated on its way to generator or boiler, and the dilute solution on its

way to absorber is cooled. This cooling of weak liquid also helps absorption and reduces the

cooling of absorber by external source.

A gas heat exchanger is used between the absorber and the evaporator. The hydrogen gas

going to the evaporator gets cooled by the cool ammonia vapor and hydrogen gas mixture.

7. It may be noted that the circulation is effected by gravity and thus no moving part in the

system is necessary.


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For electrical input to the system

1. Connect water supply and drain pipes.

2. Switch on the supply to the refrigeration circuit.

3. Take the Selector switch on the panel to Electrical position.

4. Take the Fuel Selector switch to I position.

5. Ensure that Thermostat is set to 3.

6. Note all the readings of the temperatures T1, T2, T3 .T6 on the temperature indicators

and power on the power indicator.

7. Wait for approximately 45 min and start the water supply. Adjust the supply to be

between 2 to 3 lph. To set the water flow rate, there is a valve provided near the point

where there is water inlet connection.

8. Note the readings in the observation table every 10 min.

9. Take the readings till the system stabilizes. This is indicated by constant reading of the

outlet water over two subsequent readings.

For LPG input to the system

1. Connect water supply and drain pipes.

2. Switch on the supply to the refrigeration circuit.

3. Take the Selector switch on the panel to LPG position.

4. Take the fuel selector switch to LPG position. (There is an icon of flame to indicate

LPG).

5. Ensure that thermostat is set to 3.

6. Ensure that the flow control knob on the LPG rotameter is fully open.

7. Note all the readings of the temperatures T1, T2, T3, T4, T5 and T6 on the

temperature indicators and power on the power indicator.

8. Fire the refrigerator. To fire the refrigerator,

Ensure that the LPG is properly and correctly connected to the kit.

Ensure that the LPG rotameter knob is fully open.


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At the bottom panel of the trainer there are two buttons, next to the Thermostat

knob. Keep the button marked PUSH1 pressed. While keeping this pressed,

press the button marked PUSH2.

Observe the flame in the window provided for this.

Once you observe the flame, leave the button PUSH1

You may have to press the button PUSH2 multiple times in succession toobtain flame.

9. Wait for approximately 45 min and start the water supply. Adjust the supply to be

between 2 to 3 lph. To set the water flow rate, there is a valve provided near the

point where there is water inlet connection.

10. Note the readings in the observation table every 10 min. Refer sample observation

table enclosed.

11. Take the readings till the system stabilizes. This is indicated by constant reading of

the outlet water over two subsequent readings.

Formulae:

For electrical input to the system

1. To find COPactual

lph Density of water sec

m kg/sec3600 1000

V t

5 6kg kJ

(W) ( - ) K 1000s Kg K

Q m Cp T T

Cp = Specific heat of water = 4.186 KJ/ kg-K

Actual

(W)COP

(W)in

Q

P

2. To find COPideal

ideal

COPg ae

c e g

T TT

T T T


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For LPG input to the system

1. To find COPactual

lph Density of water sec

m kg/sec 3600 1000

V t

5 6kg kJ

(W) ( - ) K 1000s Kg K

Q m Cp T T

Cp = Specific heat of water = 4.186 KJ/ kg-K

Actual

(W)COP

(W)in

Q

P

inkg hr KJ

P W Calorific Value of LPG3600 kg

in

G

Calorific Value of LPG = 50000 KJ/kg

2. To find COPideal

g

ag

ec

eIdeal

T

TT

TT

TCOP

Nomenclature:

T1 = evaporator temperature (Te)

T2 = chamber temperature

T3 = condenser temperature (Tc)

T4 = absorber temperature (Ta)

T5 = temperature of water inlet (Tci)

T6= temperature of water outlet (Tco) T7= generator temperature (Tg)

Exercises:


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1. Determine the coefficient of performance (COP) of vapor absorption refrigeration

trainer


1. Ensure that the vapor absorber trainer is installed on plane rigid and horizontal surface

away from the wall.

2. Connect 230 V A. C. supply to the trainer by connecting 3 pin connector to the power

supply socket in the laboratory.

3. Ensure that the LPG is properly and correctly connected to the kit.


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Experiment 13

AIR CONDITIONING TRAINER

Theory:

An Air Conditioning System is defined as an assembly of different parts of the

system used to produce a specified condition of air within a required space or building. An

ideal air-conditioning system should maintain correct temperature, humidity, air-purity, air

movement and noise level. Always, it is not possible to maintain all the above factors

mentioned and a compromise should be made to make the system economic.

The air-conditioning systems are mainly classified as:

1. Central station air-conditioning system.

2. Unitary air-conditioning system.

3. Self-contained air-conditioned units.

Central Station Air-Conditioning System

In a central air-conditioning system, all the components of the system are grouped

together in one central room and conditioned air is distributed from the central room to therequired places through extensive duct work.

The central air-conditioning system is generally used for the load above 25 tons of

refrigeration and 2500 m3/min. of conditioned air.

Unitary Air-Conditioning System

All the components of the unitary air-conditioned system are assembled in the

factory itself. These assembled units are usually installed in or immediately adjacent to a

zone or space to be conditioned. It is commonly preferred for 15 tons capacity or above or

around 200 m3/min. of air flow. Recently even 100 tons capacity units are also

manufactured.

Self-contained Air-conditioning Units

Self-contained units are available in wide variety of sizes and for many specific

purposes. The following three types are commonly available in the market.

a. Room cooler


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b. Store-coolers

c. Residential Air-conditioning Unit.

The air-conditioning systems on the basis of application groups are:

a. Comfort air-conditioning and

b. Industrial air conditioning.

The essential feature of comfort air-conditioning system is to provide an

environment which is comfortable to the majority of the occupants.

The comfort air-conditioning systems are sub divided into three groups.

1. Summer air conditioning

The problem encountered in summer air-conditioning is to reduce the sensible heat

and the water vapor content of the air by cooling and dehumidifying.

2. Winter air-conditioning

The problem encountered in winter air-conditioning is to increase the sensible heat

and the water vapors= content of the air by heating and humidification.

3. Year-round air-conditioning

This system assures the control of temperature and humidity of air in an enclosed

space throughout the year when the atmospheric conditions are changing as per

season. Industrial air-conditioning provides air at required temperature and humidity

to perform a specific industrial process successfully. The design conditions are not

based on the feeling of the human beings but purely on the requirement of the

industrial process.

Description:

The compressor is used for pumping the refrigerant through the system.

The condenser is the forced air-cooled type for which condenser fan and motor has

been provided.

Capillary is provided as an expansion device for evaporator.

A temperature indicator with eight point selection switch has been provided to get

the various temperatures viz.


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T1 Refrigerant temperature at suction.

T2 Refrigerant temperature at discharge.

T3 Refrigerant temperature before expansion.

T4 Refrigerant temperature after expansion.

T5 Dry bulb temperature of air at suction.

T6 Dry bulb temperature in chamber.

T7 Wet bulb temperature in chamber

The selection of any of the temperature can be made by rotating the selection switch

to the respective channel.

We have provided pressure gauges for indicating gas pressures at compressor suction

P1, compressor discharge P2, after condenser P3, after thermostatic expansion valve

P4.

An energy meter provided for measuring power input to compressor.

We have supplied a steamer to generate the steam or hot water as per the

requirements of the experiment. Steam piping has been done to enable the user to

inject steam in air inlet duct and / or test cabin.


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Experiment No: 13a

Objective:

To determine the Coefficient of Performance (COP) of air conditioning system in open

type ducting

Air Damper Position:

Air inlet damper Open 100%

Air outlet damper Open 100%

Air circulation damper Closed 100%

Experimental Procedure:-

1. Keep the status of air damper positions and expansion device selection as given

above.

2. Switch on mains supply and compressor supply.

3. By using selector switch on temperature Indicator, note the temperature T1, T2, T3,

T4,T5, T6, T7 in the observation table.4. Note the pressures of gas in the circuit by noting P1, P2, P3, P4 pressures in the

observation table.

5. Note down the energy-meter reading for compressor.

6. Repeat the above procedure to get different sets of readings till you get fairly

constant pressures of the consecutive readings. Confirm this by taking one more set

of readings.


8. Switch off all the switches after you complete the experiment.


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Formulae:

1. C.O.P (Reversed Carnot) 1

2 1

T

heat transfer manual for printing

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