Manual for Heat Transfer Operations

List of Experiments:

Sl No Experiment Name Page Number

1. Composite wall.

2. Natural Convection.

3. Forced Convection.

4. Thermal Conductivity of liquid.

5. Thermal conductivity of a metal rod.

6. Heat transfer through a pin fin.

7. Emissivity measurement.

8. Critical Insulation Thickness

9. Dropwise and Filmwise condensation.

10. Double pipe heat exchanger.

11. Shell and Tube Heat exchanger.

12. Rising film evaporator

13. Heat transfer through agitated vessel

14. Boiling heat transfer

EXPERIMENT NO: 1

NAME OF EXPERIMENT : COMPOSITE WALL

OBJECTIVE:Study of conduction heat transfer in composite wall.

AIM:To determine total thermal resistance and thermal conductivity of composite wall To plot temperature gradient along with composite wall structure.

INTRODUCTION:When a temperature gradient exists in a body, there is an energy transfer from the high temperature region to the low temperature region. Energy is transferred by conduction and heat transfer rate per unit area is proportional to the normal temperature gradient.

When the proportionality constant is inserted

Where q is the heat transfer rate and is the temperature gradient in the direction of heat

flow. The positive constant k is called thermal conductivity of the material.

THEORY:A direct application of Fourier’s law is the plane wall.

When the thermal conductivity is considered constant. The wall thickness is X, and T1 and T2 are surface temperatures. If more than one material is present, as in the multiplayer wall, the analysis would proceed as follows: The temperature gradients in the three materials, the heat flow may be written.

=

The heat flow must be same through all sections. Solving these three equations simultaneously, the heat flow is written as

DESCRIPTION:The Apparatus consists of a heater sandwiched between two asbestos sheets. Three slabs of different material are provided on both sides of heater, which forms a composite structure. A small press- frame is provided to ensure the perfect contact between the slabs. A variac

is provided for varying the input to the heater and measurement of input power is carried out by a digital voltmeter & Digital Ammeter.

Temperatures sensors are embedded between inter faces of the slab, to read the temperature at the surface. The experiment can be conducted at various values of power input and calculation can be made accordingly.

UTILITIES REQUIRED:Electrically supply: 1 phase, 220 V AC, 2 Amp.Table for set up support

EXPERIMENTAL PROCEDURE:1) Start the supply of heater by varying the dimmerstat; adjust the power input at the

desired value.2) Take readings of all the temperature sensors after fairly steady temperatures are

achieved and rate of rise is negligible.3) Note down readings in the observation table.

SPECIFICATION:Slab size:Cast Iron : Diameter = 250 mm, thickness = 20 mmBakelite : Diameter = 250 mm, thickness = 16 mmPress wood: Diameter = 250 mm, thickness = 12.7 mmHeater : Nichrome heater (400watt) wounded on mica and insulated with Mica and asbestos is providedControl form: The control panel consists of digital voltmeter, digital temperature Indicator with multi channel switch, variac to control the heat Input to the heater.

Temp sensors: RTD PT – 100 type (8 nos)Wooden cabinet is provided to accommodate the slab assembly. Whole assembly is fitted on a MS powder coated base plate to give the setup more strength and rigid ness.

OBSERVATION & CALCULATION :

DATA:Slab size Cast Iron : Diameter = 250 mm, thickness = 20 mmBakelite : Diameter = 250 mm, thickness = 16 mmPress wood: Diameter = 250 mm, thickness = 12.7 mmHeater : Nichrome heater 400 Watt) wounded on mica and insulated with

lpppmica and asbestos is provided.Control Panel: The control panel consists of Digital Voltmeter, Digital Ammeter,

Digital temperature indicator with multi channel switch, Variac to control the heat input to the heater.

Temp. Sensor: RTD PT-100 type (8nos.)

Wooden cabinet is provided to accommodate the slab assembly. Whole assembly is fitted on a MS Power coated base plate to give the setup more strength and rigidness.

OBSERVATION TABLE:

VoltageV

AmpereA

Heat Temperature sensors readings ºC

Input T1 T2 T3 T4 T5 T6 T7 T8 0CW=V*IAt x=0At x=25mmAt x=44mmAt x=56.7 mm

T7

T5

Press woodBakelite T3

Cast Iron T1

HeaterT2

T4

T6

T8

NOMENCLATURE:B = Total thickness of composite slab.Q = Heat supplied by the heaterT1 & T2 = Interface temperature of cast Iron and heaterT3 & T4 = Interface temperature of cast Iron and bakeliteT5 & T6 = Interface temperature of bakelite and press woodT7 & T8 = Top surface temperature of press woodX1 = Cast Iron thickness X2 = Bakelite thicknessX3 = Press wood thickness Rt = Slab SensitivityK = Metal conductivity

PRECAUTION & MAINTENANCE INSTRUCTIONS:

1) Use the stabilize AC single phase supply only

2) Never switch on mains power supply before ensuring that all the ON/OFF switches given on the panel are at OFF position

3) Voltage to heater starts and increase slowly4) Never run the apparatus if power is less than 180 V and more than 240 V5) Operate selector switch of temperature indicator gently6) Always keep he the apparatus free from dust.7) There is a possibility of getting abrupt result if the supply voltage is fluctuating or

if the satisfactory steady state condition is not reached.

TROUBLESHOOTING:

1) If electrical panel is not showing the input on the mains light. Check the fuse and also check the main supply

2) If DTI displays “1” on the screen check the computer socket if loose tight it.3) If temperature of any sensor is not displays in DTI check and rectify that4) Voltmeter showing the voltage given to heater but ampere meter does not. 5) Tight the heater socket & switch if ok it means heater burned.

EXPERIMENT NO: 2

NAME OF EXPERIMENT: HEAT TRANSFER IN NATURAL CONVECTION

OBJECTIVE:Study of convection heat transfer in natural convection.

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

INTRODUCTION:Convection is defined as process of heat transfer by combined action of heat conduction and mixing motion. Convection heat transfer is further classified as natural convection ans forced convection.

If the mixing motion takes place due to density difference caused by temperature gradient, then the process of heat transfer is known as heat transfer by Natural of Free Convection. If the mixing motion is induced by some external means such as a pump or blower then the process is known as heat transfer by Forced Convection.

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 Indictor measure the temperature at the different point 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.

UTILITIES REQUIRED:Electricity supply: 1 Phase, 220 V AC, 2 Amp.Table for set-up support

EXPERIMENTAL PROCEDURE:

STARTING PROCEDURE:

1. Clean the apparatus and make it free from Dust, first.2. Ensure that all On /Off Switch 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 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 min. record the temperature of test section at various points in each 5 min.

interval.8. If the temp. Readings are same for three times, assume that steady state is achieved.9. Record the final temperatures.

CLOSING PROCEDURE:

1. When experiment is over ,switch off the heater first.2. Adjust variac to zero.3. Switch off the panel with the help of mains on/off switch given on the panel.4. Switch off power supply to panel.

SPECIFICATION:Diameter of tube = 35 mmLength of the tube = 500 mm Size of duct = 25 cm X 25 cm X 90 cmTemperature sensors = RTD PT-100 typeNo. of RTD Temperature sensors = 8 Nos.Digital Voltmeter = 0 to 500 VDigital Ammeter = 0 to 10 Amps.Dimmerstat = 2 Amps/220 V.Heater = 400 watts.Temperature indicator = Digital Temperature Indicator 0 to 2000 C

with multi channel switch.

FORMULAE:

1. The heat transfer coefficient is given by

Where

q = Heat transfer rate = V I (K Cal/Hr.)

As = Area of the heat transferring surface.= πd L m2

2.

Ts = Ambient temperature in duct 0C = T8

OBSERVATION & CALCULATIONS:

Outer diameter of Cylinder, d = 35mm.

Length of Cylinder, L = 500mm.Input to heater = V x I, Watts.Where V = Volts.I = Amps.

Run No. VVolts

IAmps

ºCT1 T2 T3 T4 T5 T6 T7 T8

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

switches given on the panel are at off position.3. Voltage to heater starts and increase slowly.4. keep all the assembly undisturbed.5. Never run the apparatus if power supply is less than 180V and above 240 V.6. Operate selector switch of temperature indicator gently.7. Always keep the apparatus free from dust.8. There is a possibility of getting abrupt result if the supply voltage is fluctuating

or if the satisfactory steady state condition is not reached.

TROUBLESHOOTING:1. If electric panel is not showing the input on the mains light. Check the fuse

and also check the main supply.2. If D.T.I displays “1” on the screen check the computer socket if loose tight

it.3. If temperature of any sensor is not displays in D.T.I. check the connection

and rectify that.4. Voltmeter showing the voltage given to heater but ampere meter does not. 5. Tight the heater socket & switch if ok it means heater burned.

EXPERIMENT NO:3

NAME OF EXPERIMENT: HEAT TRANSFER IN FORCED CONVECTION

AIM :To find surface heat transfer coefficient for a pipe flowing heat by force convection to air flowing through it, for different air flow rate and heat flow rate.

THEORY:Air flowing into the heated pipe with very high flow rate the heat transfer rate increases. The temperature taken by the cold air from the bulk temperature and rises its temperature. Thus, for the tube the total energy added can be expressed in terms of a bulk-temperature difference by

q = m Cp ( Tb2 – Tb1 )

Bulk temperature difference in terms of heat transfer coefficient

q = hA ( Tb2 – Tb1 )

A traditional expression for calculation of heat transfer in fully developed turbulent flow in smooth tubes is that recommended by Dittus and Boelter.

Nud = 0.023 Red 0.8 Pr n

If n = { 0.4 for heating of the fluid{ 0.3 for cooling of the fluid

UTILITIES REQUIRED:Electricity Supply : 1 Phase, 220 V AC, 10Amp.Floor area of 1.2 m x 0.5 m.

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 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. Air flow is measured with the help of Orifice meter and the water manometer fitted on the board.

EXPERIMENTAL PROCEDURE:

STARTING PROCEDURE:1. Clean the apparatus and make it free from Dust.2. Put Manometer Fluid (water) in Manometer connected Orifice meter.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 temperature.13. Record manometer reading.

CLOSING PROCEDURE:1. When experiment is over, switch off heater first.2. Switch off Blower.3. Adjust Variac to Zero.4. Switch off the Panel with the help of Mains On/Off Switch given on the Panel.5. Switch off Power Supply to Panel.

STANDARD DATA:Length of test section = 412 mmI.D. of test section = 32 mmO.D. of test section = 38 mmNo. of RTD Temperature Sensors = 6 mmBlower = ½ H.P.Orifice Diameter = 14 mmOrifice pipe inside diameter = 2 Amp,220 VDigital temperature indicator with multichannel switch Digital Voltmeter & Digital Ammeter are also provided.

FORMULAE:

1.

2.

3.

4.

OBSERVATION TABLE:

VVOLT

IAMPS

T1

OCT2

OCT3

OCT4

OCT5

OCT6

OCManometer

Reading(cm)

OBSERVATIONS:

Inner dia of test section, Di = -------------- mmOuter dia of test section, Do = -------------- mmLength of test section, L = -------------- mmDiameter of orifice, = -------------- mm

Temperature sensors readingsT1 = -------------- OC Air inlet temp.T2 = -------------- OC Surface temp. of test section T3 = -------------- OC Surface temp. of test sectionT4 = -------------- OC Surface temp. of test sectionT5 = -------------- OC Surface temp. of test sectionT6 = -------------- OC Air outlet temp.

Manometer Reading H = -------------- Meters.

CALCULATIONS:

Heat Transfer Coefficient

Qa the rate at which air is getting heating is calculated as follows :

Qa = m Cp ∆T K cal/Hr.

Where:

M = Mass flow rate of air Kg/Hr.Cp = Specific heat of air K cal oC Kg.∆T = Temp. rise in air oC (T6 − T1)m = Q f afa = Density of airQ = Vol. flow rateQ = Cd π / 4d2 √ 2g H f w / f a (m3 /Hr )

U =

Cd = Coefficient of discharge = 0.60H = Difference of water level in manometer in meters.Pw = Density of water 1000 kg/m3

Pa = Density of air at inlet temp. = 1.205 kg/m3

d = Diameter of Orifice = 0.014A = Test section area = π Di L m2

Ta = Average temperature of air

Ts = Average surface temperature

Using this procedure obtain the values of Ha for different air flow rates.

PRECAUTIONS & MAINTENANCE INSTRUCTIONS:1. Use the stabilize A.C. Single phase supply only2. Never switch on mains power supply before ensuring that all the ON/OFF

switches given on the panel are at OFF position.3. Voltage to heater start and increase 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.8. There is a possibility of getting abrupt result if the supply voltage is fluctuating or if

the satisfactory steady state condition is not reached.

TROUBLE SHOOTING:

1. If electric panel is not showing the input on the mains light. Check the fuse and also check the main supply.

2. If D.T.I. displays “1” on the screen check the computer socket if loose tight it.3. If temperature of any sensor is not displays in D.T.I. check the connection and

rectify that.4. Voltmeter showing the voltage given to heater but ampere meter does not. 5. Tight the heater socket & switch if ok it means heater burned.

REFERENCES:

1. Heat Transfer by J.P. Holman, 8th Edition, of Mc Graw Hill2. Process Heat Transfer by Donald Q Kern, of Mc Graw Hill

EXPERIMENT NO: 4

NAME OF EXPERIMENT: THERMAL CONDUCTIVITY OF LIQUID(GUARDED PLATE METHOD)

OBJECTIVE:Study of heat transfer through liquid.

AIM:To determine the Thermal Conductivity of a liquid

INTRODUCTION:When a temperature gradient exists in a body, there is an energy transfer from the high temperature region to the low temperature region .energy is transferred by conduction and heat transfer per unit area is proportional to the normal temperature gradient:

when the proportionality constant is inserted,

where q is the heat transfer rate and the temperature gradient in the direction of heat

flow. The positive constant k is called thermal conductivity of the material.

Heat transfer area = Ah (Area Perpendicular to the direction of heat flow)

DESCRIPTION:The apparatus is based on well established “Guarded Hot Plate” method. It is a steady state absolute method suitable method for materials, which can be fixed between two plates and can also be extended to liquids that fill the gap between the plates.

The essentials components of the set up are the hot plate, 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.

Th

Tc

ΔX

In the set up, a unidirectional heat flows takes place across the liquid whose 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 sensors readings are used as and 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 samples of high viscosity and density shall further ensure the absence of convection and the heat transfer can be safely assume to take place by conduction alone.

UTILITIES REQUIRED: Water supply 5 lit/min (approx)Drain.Electricity supply: 1 phase, 220 V AC, 2 Amp.Table for set – up support

EXPERIMENTAL PROCEDURE:1. Fill the liquid cell with the sample liquid (glycerol) through the inlet port,

keeping the apparatus tilted towards upper side so that there is complete removal of air through outlet port. Liquid filing 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.

2. Allow cold water to flow through cold water inlet.3. Start the electric heater to heat the hot plate. Adjust the voltage of hot plate

heater in the range of 10 to 15 volts.4. Adjust the cold water flow rate such that there is no appreciable change in the

outlet temperature of cold water(there should be minimum change).5. Go on recording the thermocouple reading 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 is no appreciable change in the thermocouple readings ±0.1ºC) record the three thermocouple readings on the hot side (Th1, Th2, Th3, ie T1,T2, T3) and the three thermocouple readings (Tc1, Tc2, Tc3, ie T4,T5, T6) on the cold side along with the voltmeter (V) and ammeter (A) readings.

6. Stop the electric supply to the heater and continue with the supply of cold water till there is a decrease in the temperature of hot plate (may be for another 30 – 40 mins).

7. Open the liquid outlet valve slightly in the downward tilt position and drain the sample liquid in a receiver, keeping liquid port open.

SPECIFICATION:1. Hot plate

Material = copper Diameter = 180 mm

2. Cold plate Material = copper Diameter = 180 mm

3. Sample liquid depth = 16 mm

4. Temp. sensors = RTD PT- 100 type Quantity = 6 Nos.

= No. 1 to 3 mounted on hot plate = No. 4 to 6 mounted on cold plate.

5. Digital temperature indicator Range = 0 0C to 199.9 0C Least count = 0.1 0C

6. Variac = 2 amp, 230 V AC 7. Digital voltmeter = 0 to 500 Volts 8. Digital ammeter = 0 to 10 Amp.9. Heater = Nichrome heater (400 Watt)

FORMULAE:

OBSERVATION TABLE:

Sl.No

V Volts

I Amps

W Watts

Th1

ºCTh2ºC Th2ºC Th3ºC Tc1ºC Tc2ºC Tc3ºC Cold

water flow rate

RECORD THE FOLLOWING AT STEADY STATE:

Sample liquid:Volt meter reading = VAmmeter reading = AHot face average temperature, Th = (Th1 + T h2 + T h3)/3 Cold face temperature, Th = (T c1 + T c2 + T c3)/3

PRECAUTIONS & MAINTENANCE INSTRUCTIONS:1. Use the stabilized A.C Single Phase supply only.2. Never switch on mains power supply before ensuring that all the ON/OFF switches

given 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 the 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.8. Testing liquid should be filled fully.9. There is a possibility of getting abrupt result if the voltage is fluctuating or if the

satisfactory steady state condition is not reached.

TROUBLESHOOTING:1. If electric panel is not showing the input on the mains light. Check the fuse and also

check the main supply.2. If D.T.I. displays “1” on the screen check the computer socket if loose tight it.3. If temperature of any sensor is not displays in D.T.I. check the connection and

rectify that4. Voltmeter showing the voltage given to heater but ampere meter does not. 5. Tight the heater socket and switch if ok it means heater burned and replace that.

EXPERIMENT NO: 5

NAME OF EXPERIMENT: THERMAL CONDUCTIVITY OF METAL ROD

OBJECTIVE:Study of conduction heat transfer in metal rod

AIM:To determine the thermal conductivity of metal bar

THEORY:The heater will heat the bar on its end one and heat will be conducted through the bar to the other end. Since the rod is insulated from outside, it can be safely assumed that the heat transfer along the copper rod is mainly due to axial conduction and at steady state the heat conducted shall be equal to the heat absorbed by water at the cooling end. The heat conducted at steady state shall create a temperature profile within the rod. [T = f (x)]. The steady state heat balance at the rear end of the rod is:

Heat absorbed by cooling water.Q = MCp ∆T

Heat conducted through the rod in axial direction:

at steady state

So thermal conductivity of rod may be expressed as,

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 values of dT/dX is obtained as the slope of the graph between T vs. X

DESCRIPTION:The apparatus consists of a metal bar, one end of which is heated by an electric heater while the other end of the bar projects inside the cooling water jacket. The middle portion of the bar is surrounded by a cylindrical shell filled with the asbestos insulated powder. The temperature of the bar is measured at different section. The heater is provided with a dimmerstat for controlling the heat input, water under constant head conditions is circulated through the jacket and its flow rate and temperature rise are noted by two temperature sensors provided at the inlet and outlet of the water.

UTILITIES REQUIRED:

Electricity Supply: 1 phase, 220 V AC, 2 ampsWater supplyDrainTable for setup support

EXPERIMENTAL PROCEDURE:

STARTING PROCEDURE:1) Connect cold water supply at inlet of the cooling chamber.2) Connect outlet of the cooling chamber to drain.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) Start water supply (say 2 LPM approx) at constant head.6) Now switch on the main power supply7) Switch on the panel with the help of mains on/off switches given on the panel8) Fix the power input to the heater with the help of variac, voltmeter and Ammeter

provided.9) After 30 minute start recording the temperature of various points at each 5 minutes

interval.10) If temperature readings are same for three times assume that steady state is achieved.11) Record the final temperature.

CLOSING PROCEDURE:1) When experiment is over, switch off heater first.2) Adjust variac at zero.3) Switch off the panel with the help of mains on/off switch given on the panel.4) Switch off power supply to panel.5) Stop cold water supply.

FORMULAE:

SPECIFICATION:Length of the metal rod = 450 mmDia of the metal rod = 25 mmTest length of the bar = 235 mmTotal no. of temp. sensors in the setup = 8 no.No. of temp. Sensors Mounted on the bar = 6 noNo. of temp. Sensors mounted on water jacket = 2 noType of temperature sensor = RTD PT-100Heater = Nichrome heater (400 w)Cooling jacket dia = 100 mmLength of cooling jacket = 75 mmDimmerstat for heater coil = 2 amp, 230 VACDigital Voltmeter = 0 to 500 Volts ACDigital Ammeter = 0 to 10 Amp

Temperature indicator digital temperature indicator 0 0C to 199.9 0C and least count 0.1 0C with multi channel switch.

OBSERVATION & CALCULATION:

TempSensor No.

1 2 3 4 5 6 7 8

SteadyState temp

Temp sensor no along the axis Distance from leading edge (hot end) of the rod, X (mm)

T1 35

T2 75

T3 115

T4 155

T5 195

T6 235

T7 is the inlet temp of cold waterT8 is the outlet temp of cold water

CALCULATION:

Heat gained by water (at steady state) Q = M Cp (T8-T7) Kcal/hrHeat transfer area for axial conduction A =

D is the diameter of copper rodPlot T vs. X. draw a smooth curve through all the points and obtain the slope dT/dX at x=L or using least square method fit the T vs. X data to a polynomial and thus obtain the slope dT/dx at x=L. Express the slope in 0C /m.

Calculate the value of thermal conductivity of metal bar, k from:

Compare it with the literature value of =332 k Cal/h-m0C. Discuss the sources of error, if any.

PRECAUTIONS & MAINTENANCE INSTRUCTIONS:

1) Use the stabilize AC single phase supply only2) Never switch on the mains power supply before ensuring that all the on/off

switches given on the panel are at off positions.3) Voltage to heater to be starts and increase slowly.4) Keep all the assembly undisturbed.5) Never run the apparatus if power supply is less than 180 volts and above than 240

volts6) Operate selector switch of temperature indicator gently7) Always keep the apparatus free from dust.8) There is a possibility of getting abrupt result if the supply voltage is fluctuating or if

the satisfactory steady state condition is not reached

TROUBLESHOOTING:

1) If electric panel is not showing the input on the mains light. Check the fuse and also check the main supply

2) If D.T.I display “1” on the screen check the computer socket of loose tight it3) If temperature of any sensor is not displays in D.T.I check the connection

and rectify that.4) Voltmeter showing the voltage given to heater but ampere meter does not. 5) Tight the heater socket & switch if ok it means heater burned.

EXPERIMENT NO: 6

NAME OF EXPERIMENT: HEAT TRANSFER FROM A PIN FIN

OBJECTIVE:Study of convection heat transfer from a pin fin.

AIM:To study the temperature distribution along the length of a pin fin under free and forced convection.

INTRODUCTION:Extended surfaces or fins are used to increase the heat transfer rate from a surface to a fluid wherever it is not possible to increase the value of a surface heat transfer coefficient or the temperature difference between the surface and the fluid. The use of this is very common and they are fabricated in a variety of shapes circumferential fins around the cylinder of a motorcycle engine and the fins attached to condenser tubes of a refrigerator are few familiar examples.

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 effectiveness = tan h mL /mL

Temperature profile given by :

/o = [T-T b ] / [Tb - Tf ] = [cosh m (L-x) + H sinh m (L-x)/[cosh mL + H sinh mL]

Where Tf is the free stream temp. of air; Tb is the temp. of fin at its base; T is the temp. within the fin at any x ; L is the length of the fin and D is the fin diameter, m is the fin parameter defined as;

m = [h C /(kb A) ]

= 1 / [T mf + 273.15], 1 / K

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

Q = Co ( / 4) d2 [2gHw /air ] , m3/s (at temp. Tf)

Velocity of air at T 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 the blower and the air flows past the fin perpendicular to its axis. One end of the fin projects outside of duct and is heated by its heater. RTD PT – 100 type temperature sensors measures 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.

UTILITIES REQUIRED:Electricity supply: 1 phase, 220 AC, 5 Amp.Table for set-up support.

EXPERIMENTAL PROCEDURE:

NATURAL CONVECTION: Start heating the fin by switching on the heating element and adjust the voltage 0 to

80 Volt. (Increase slowly from 0 onwards) note the temperature readings No. 1 to 5.

When steady state is reached, record the final readings of temperatures sensor no. 1 to 5 and also ambient temperature No. 6.

Repeat the same experiment with various voltages = 100 volts & 120 volts.

FORCED CONVECTION:

Start heating the fin by switching on the heater element and adjust the voltage = 100 volts.

Start the blower and adjust the difference of level in the manometer H= cm with the help of fly valve provided on the pipe.

Note the temperature readings No. 1 to 5 at a interval of 5 minutes.

When the steady state is reached record the final readings of temperatures sensor no. 1 to 5 and also ambient temperature No. 6.

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

SPECIFICATIONS:Duct size = 150mm 100mm 1000mm

Diameter of the fin = 12.7mm,

Length of the fin = 125mm

Diameter of the orifice = 39mm

Diameter of the delivery tube(Int.) = 52mm

Coefficient of discharge (orifice meter) Co = 0.64

Temperature indicator = 0-200C,RTD PT –100type

RTD PT –100 type Sensors = 6Nos.

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

Thermal conductivity of fin material (Brass) = 95 Kcal/hr-m-C

Centrifugal blower with single – phase motor = 0.5 HP,2800RPM

Dimmerstat for heat input control = 230V , 2 Amp.

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

Voltmeter = 0-500 V A.C.

Ammeter = 0-10 A.

OBSERVATIONS & CALCULATIONS:

Expt PowerInput,

Fin Temp. Manometer

reading,(h) m of water

W=v*i T= (x=2.5cm) T=(x=5cm) T=(x=7.5cm) T=(x=10 cm) T=(x=12.5 cm) T=Tf

Free

Convection

Forced

Convection

FREE CONVECTION:

Mean temp of the fin, Tm = (T1 + T2 + T3 + T4 + T5) / 5

= 1/ (Tmf + 273.15)

Grashof No. Gr = (g D3 T)/ 2

Using the correlation for free convection:

Nusselt No. Nu = 0.53(Gr Pr)1/4 = h D/kair

Free convective heat transfer coeff, h = Nu kair / D

Fin parameter, m =

Perimeter, C = D

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

Fin dia. D = 12.710-3m

Fin Length, L = 12510-3m

Fin effectiveness, = tanh mL/mL

Parameter, H = h/kbm

Theoretical temperature profile within the fin

/o = [T-T b ] / [Tb - T f ] = [cosh m (L-x) + H sinh m (L-x) / [cosh mL + Hsinh mL]

Taking base temp, Tb=T1

FORCED CONVECTION:

Orifice coefficient, Co = 0.64

Volumetric flow rate of air, Q = Co(/4)d2

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

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

Velocity of air at mean (Tmf), V1 = V(Tmf + 273.15) / (Tf + 273.15)

fluid temp.

Re = DV1/

Using the correlation for force convection:

Nusselt No. Nu = 0.615(Re)0.466

Nu = hD/kair

Heat transfer coeff, h = Nu kair/D

Fin parameter m =

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

switches given on the panel are at OFF position.3. Voltage to heater start and increase 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.8. There is a possibility of getting abrupt result if the supply voltage is fluctuating or

if the satisfactory steady state condition is not reached.

TROUBLE SHOOTING:

1. If electric panel is not showing the input on the mains light. Check the fuse and also the main supply.

2. If D.T.I displays “1”on the screen check the computer socket if loose tight it.3. If temperature of any sensor is not displayed in D.T.I check the connection and rectify

that.4. Voltmeter showing the voltage given to heater but ampere meter does not. 5. Tight the heater socket & switch if ok it means heater burned.

EXPERIMENT NO: 7

NAME OF EXPERIMENT: EMISSIVITY MEASUREMENT APPARATUS

OBJECTIVE:Study of Radiation heat by black body and test plate.

AIM:To find out the emissivity of a test plate.

INTRODUCTION:All substances at all temperature emit thermal radiation. Thermal radiation is an electromagnetic wave and does not require any material medium for propagation. All bodies can emit radiation and have also the capacity to absorb all of a part of the radiation coming from the surrounding towards it.

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 nature 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 the plates 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 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.

UTILITIES REQUIRED:Electricity supply: 1 Phase, 220 V AC, 4 AmpsTable for set-up support

EXPERIMENTAL PROCEDURE:1. Gradually increase the input to the heater to black plate and adjust it to some

value viz. 50,75,100 watts and adjust heater input to test plate slightly less than the black plates viz.40,65,85 etc.

2. Check the temperature of the two plates with small time intervals and adjust the input of test plate only, by the dimmerstat so that two plates will be maintained at the same temperature.

3. This will require some trial and error and may take more than one hour of so to obtain the steady state condition.

4. After attaining the steady state conditions record the temperature and Voltmeter and Ammeter reading for both the plates.

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

SPECIFICATION:

1. Test plate dia = 160mm2. Black plate = 160 mm3. Dimmerstat for both plates = 0-2A, 0-220V.4. Voltmeter = 0-250V, Ammeter 0-2.5A5. RTD temperature sensor = 3 Nos6. Heater for test plate and black plate Nichrome strip wound on mica sheet

and sand-witched between two mica sheets of 440Watt.

FORMULAE:1. qb = A ( Ts4 - TD

4 )2. qs = σ EA ( Ts4 – TD

4 )3. E = Emissivity of specimen to be determined.

( Wb – Ws ) 0.86 = ( Eb – E ) σ A ( Ts4 – TD4 )

TD = Ambient temperature of enclosure oK

OBSERVATION & CALCULATIONS:

BLACK PLATE:

Voltage, V Amperage, I Power input, Wb = V I Black plate temp, Ts (oC)

TEST PLATE:

Voltage, V Amperage, I Wattage, Ws = V I Ts (oC) TD (oC)

The emissivity of the test plate can be calculated at various surface temperatures of the plates.

NOMENCLATURE:

qb = Heat input to disc coated with lamp black (K Cal/hr)= Wb 0.86

Wb = wattage supplied to black plate qs = Heat input to test plate (K Cal/hr)

= Ws 0.86Ws = wattage supplied to test plateσ = Stefan Boltzmann constant = 4.876 10-8 Kcal/m2 hr oK4

A = Area of disc (m2)Ts = Surface temperature of Discs oKE = Emissivity of specimen to be determined.Eb = Emissivity of black body.

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

switches given on the panel are at OFF position.3. Voltage to heater starts and increases slowly.4. Keep all the assembly undisturbed.5. Keep run the apparatus if power supply is less than 180 volts and above than

240 volts.6. Operate selector switch of temperature indicator gently7. Always keep the apparatus free from dust.

TROUBLE SHOOTING:

1. If electric panel is not showing the input on the mains light. Check the fuse and also check the main supply.

2. If D.T.I. displays “1” on the screen check the computer socket if loose tight it.

3. If temperature of any sensor is not displays in D.T.I. check the connection and rectify that.

4. If the temperature is not shown proper in D.T.I some air gap is there between the surface of the plate and the sensor. Plate that by using heat sink chemical.

5. Voltmeter showing the voltage given to heater but ampere meter does not. tight the heater socket and switch if ok it means heater burned.

EXPERIMENT NO: 8

NAME OF EXPERIMENT: CRITICAL INSULATION THICKNESS

REMARKS:Theory and practice regarding the Critical Radius of Insulation as given above reveals that –

a) The Critical radius depends upon K of insulation and h value present at cuter surface.b) At the Critical Radius the value of q is maximum and beyond Critical radius q starts decreasing c) ln many practical situations, the pipe radius is greater than & hence any amount of Insulation added becomes effective.

APPARATUS:The Apparatus consists of 4 nos. of metallic vertical pipes provided with heaters from inside. The heater input can be varied by a dimmerstat and is measured by digital voltmeter and ammeter. Thermocouples are provided on the surface to measure the temperature of pipe (T1 & T2) and also the insulation surface (T3 & T4). T5 is the temperature, at the ambient. The input to the Heater is varied in such a way that outer surface temperature is same for all the four vertical tubes. Under the steady state conditions the observations are recorded in the Table.

SCOPE OF EXPERIMENTS: 1) The experiment can be conducted for different values of heater input getting different

surface temperature of 70oC, 80oC, 90oC etc. 2) The experiments setups can be built for other Insulation, such as glass wool, wood etc.

Alternatively the value of h can also be calculated by using the correlation for vertical cylinder.

OBSERVATION TABLE :D) Length of Pipe = 150 mmL) Diameter of Pipe = 28 mm

S.NO. INSULATION THICKNESS cm

V volts I amps Q=VIWatts

T1 ºC T2 ºC

Pipe I

Pipe II

Pipe III

Pipe IV

0

0.5

1

2

r2 = 0.014 m

Where

Barepipe = r3 = r2 = 0.014 m0.5 cm Pipe = r3 = r2 + 0.005 = 0.019 ml cm pipe = r3 = v2 + 0.01 = 0.024 m2cm pipe = r3 = v2 + 0.02 = 0.034 m

K= 0.2

THEORY OF CRITICAL INSULATION THICKNESS :The problem of deciding the thickness of insulation around a pipe in order to reduce the heat loss fromits surface occurs frequently. It is natural to expect that greater insulation will result in less heat loss. The following analysis shows that this may not be always be the case,

Consider a long pipe of inner and outer radii r1 and r2 and thermal conductivity k1 having insulation (thermal conductivity k2 ) wrapped around it to a radius r It is assumed that the Heat Transfer coefficient at the radius r3 of the insulation surface is ho while the heat transfer coefficient, at the inner surface of the pipe is h1.

From the equation the heat transfer rate for a length L is given by –L = Length of pipe.

If q is plotted as a function of r3 other parameters being held constant, it will some time be seen to pass through a maximum for a certain r3, This value called the critical radius is obtained by differentiating the denominator of equation with respect to r and equating to zero, i.e. by minimizing the denominator since the numerator is constant. Thus –

Equation indicates that if we have a pipe whose outer radius r is less than the critical radius, then the-addition of Insulation will increase the heat loss from the pipe until r3 = (r3) critical The addition of insulation thereafter will reduce the heat loss from the pipe. On the other hand if r2 ≥ (r3) critical then the addition of insulation will immediately reduce the heat loss from the pipe.

The result obtained can be physically explained in terms of thermal resistances. The heat flow rate q is governed by the thermal resistance of the insulation and the thermal surface. Where as resistance of the insulation increases with r3 the resistance on the outer surface decreases Upto if the critical radius, the rate of decrease is greater than the rate of increase and the heat flow rate consequently increases. Beyond the critical radius, the rate of increase of the thermal resistance of the insulation is greater than the rate of decreases of the thermal resistance on the outer surface and consequently the heat flow rate decreases.

THE FOLLOWING EXAMPLE ILLUSTRATES THE ABOVE THEORY:

Asbestos insulation (k = 0,20w / m - k) is put on a steel pipe (1.6 cm I.D, 2 cm OD). Hot water at 900C flows through tile pipe and the heat transfer coefficient h1 is 500w / m2 - k. Heat is lost from the outer

surface by natural convection to surrounding it at 300C and the heat transfer coefficient (h1) is w / m2 - k. Calculate the heat loss rate per meter length of the pipe of insulation thickness of 0, 0.5, 1, 2, 3, 4 & 5cm. Plot the results discuss the variations obtained.

Neglecting the thermal resistance of the metal pipe in comparison to the other resistance, we have from equation

The results obtained are given in Table and also plotted in Fig.

Insulation Thickness(cm)

r (m) Heat Loss rate per mtr.(w/m)

0 0.01 36.80.5 0.015 42.21 0.02 43.32 0.03 41.53 0.04 38.94 0.05 36.65 0.06 34.7

50

40

30

20

10

0 0 1 2 3 4 5

It is seen that the heat loss rate first increases with the insulation thickness, reaches a maximum and then decreases. Thus this obviously because the outer radius of the pipe (r2) is less than the critical radius, this is confirmed from equation which gives -

Since the Value of the heal loss rate with a 4 cm thick insulation is equal to the Value With no insulation, we conclude that in the present case a thickness is greater 4 cm is required in order to reduce the heat loss rate.

EXPERIMENT NO: 9

NAME OF EXPERIMENT: DROPWISE & FILMWISE CONDENSATION

OBJECTIVE: To study of heat transfer in the process of condensation.

AIM:To find the heat transfer co-efficient for Drop wise Condensation and Film wise Condensation process.

INTRODUCTION:In all applications, the steam must be condensed as it transfer heat to a cooling medium hot water in a heating calorimeter, sugar etc. during condensation very high heat fluxes are possible & provided the heat can be quickly transferred from the condensing surface to the cooling medium, heat exchangers using steam can be compact & effective.

THEORY:Steam may condense on to a surface in two distinct modes, known as Film Wise & Drop wise. For the same temperature difference between the steam & the surface, drop wise condensation is much more effective than film wise & for this reason the former is desirable although in practical plants it rarely occurs for prolonged period:-

FILM WISE 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 surface is vertical or horizontal, etc.

Fresh vapour 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 downwards & 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 account for most of the difference between the effectiveness of film wise and drops wise condensation.

DROP WISE 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 static beads along its downwards in its trail. Tha ‘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, film wise condensation is normal (Although many bare metal surface 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 houses two water cooled copper condensers, one of which is chromium plated to promote drop wise condensation and the other is in its natural state to give film wise 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 temp indicator provided has multipoint connections, which measures temp of steam, two condensers, water inlet & outlet temp of condenser water flows.

UTILITIES REQUIRED:Water supply – 5ltr/minElectricity supply- 1 phase 220 V AC, 1.5 kWTable for set up support

EXPERIMENTAL PROCEDURE: 1) Fill water in steam generator by operating 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 & ON the heated 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 tube & fall down in the cylinder.5) Depending upon type of condenser under test drop wise or film wise can be

visualized.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 temperature, water flow rates, pressure are note down in the observations table at the end of each set.

SPECIFICATION:Condensers : One chromium plated for dropwise condensation & one natural

finish for filmwise condensation otherwise identical in construction. 20 mm OD, 16 mm length, Fabricated from copper with reverse flow in concentric tubes. Fitted with temperature sensor for surface temp. measurement.

Main unit : MS Fabricated construction comprising test section & steam generation section. Test section is provided with glass cylinder for visualization of the process.

Steam Generator : 8Ltrs. (Approx.) made of stainless steel with 1.5 KW heater insulated with ceramic wool.

Control valve : one each for Steam, Cooling water & drain.Instrumentation : 1) Temperature Indicator: Digital 0-199.9 0C & least count 0.10C with multi- channel switch. 2) Temperature Sensors: RTD PT- 100 Type. (6Nos.) 3) Rota meter: Standard Make 100 LPH capacity for measuring water flow rate. 4) Pleasure Gauge: Dial type 0-2 Kg/cm2

5) Temperature Controller: Digital 0-199.9 0C & least count 0.10C (for steam generator)

FORMULAE:

FOR PLANE CONDENSER

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

FORMULAE:

FOR PLATED CONDENSER

Where, g = Acc. Due to gravity = 9.8 m/sec2

L = Length of condenser = 160 mm.

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

OBSERVATIONS & CALCULATIONS:

S. No

Steam pressure kg/cm2

Water flow rate lph

Condenser under test

Plated condenser outer surface T1

Steam T2

Plain condenser outer surface T3

Steam T4

Water outlet from condenser T5

CALCULATION:

Normally steam will be pressurized. But if pressure gauge reads some pressure then properties of steam should be taken at that pressure or other wise atmospheric pressure would be taken. We will first calculate the heat transfer coefficient inside the condenser under test. For this property of water are taken at bulk mean temperature of water where i.e. (Twi + Two )/2 Where are water Twi and Two are water inlet & outlet temperatures. Following property are required-

ρ1= density of water kg/cm3

v1= kinematics viscosity m2/sec

k1= thermal conductivity

Pr= prandtl number.

Now calculate Reynolds number-

If this value of Re 2100 then flow is turbulent and below this value flow is laminar

Normally flow will be turbulent in the tube.

Now Nussle Number

Nu1 = 0.023(Red)0.8 (Pr)0.4

Now calculate heat transfer coefficient on outer surface of the condenser (h0). For this property of water are taken at bulk mean temperature of condensate i.e.

Property needed is –

Ρ2 = density of water kg/cm3

K2 = thermal conductivity

µ = viscosity m2/sec

λ = heat of evaporation

From these value overall heat transfer co efficient can be calculated

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 film wise condensation. Results may vary from theory in some degree due to unavoidable heat losses.

NOMENCLATURE:

Di = Inner Dia of condenser. = 1.7 cm

hi = Inside Heat transfer Coefficient

Ts = Temperature of steam 0C

Tw = Temperature of condenser wall 0C

g = Acc. Due to gravity = 9.8 m/sec2

L = Length of condenser = 160 mm

= Density of water kg/m3

v = Kinematics Viscosity m2 /sec.

k = Thermal conductivity k cal/hr.m0C (W/m 0C)

PRECAUTION & MAINTENANCE INSTRUCTION:

1) Use the stabilize AC single phase supply only2) Never switch on mains power supply before ensuring that all the ON\OFF switches

given on the panel are at Off position.3) Voltage to heater starts and increases slowly4) Keep all the assembly undisturbed5) Never run the apparatus if power supply is less than 180 & more than 2406) Operate selector switch of temp indicator7) Do not start heater supply unless water is filled in the test unit8) Always keep the apparatus free from dust

TROUBLE SHOOTING:

1) If electric panel is not showing the input on the mains light. Check the fuse and also check the main supply

2) If DTI displays 1 on the screen check the computer socket if loose tight it3) If temperature of any sensor is not displays in DTI check the connection and rectify

that4) Voltmeter showing the voltage given to heater but ampere meter does not. Tight the

heater socket & switch if ok it means heater burn.

EXPERIMENT NO: 10

NAME OF EXPERIMENT : DOUBLE PIPE HEAT EXCHANGER PARALLEL FLOW / COUNTER FLOW HEAT EXCHANGER

OBJECTIVE:To study the heat transfer phenomena in parallel / counter flow arrangements.

AIM:To calculate overall heat transfer coefficient for both type of heat exchanger.

INTRODUCTION :

Heat Exchanger is 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,

THEORY :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 ones.

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

1) Parallel Flow in which fluids flow in the same direction.

2) Counter Flow in which they flow in opposite direction and

3) Cross Flow in which they flow at right angles to each other.

A simple example 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 it. The heat transfer takes place across the walls of the inner tube.

DESCRIPTION:The apparatus consists of a tube in tube type concentric tube heat exchanger. The hot fluid is hot water which is obtained from an insulated water bath using a magnetic drive pump and it flow through the inner tube while the cold fluid is cold water flowing through the annuals.

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.

RTD PT-100 type sensors measure the temperature. For flow measurement Rotameters are provided at inlet of cold water and outlet of hot water line. The readings are recorded when steady state is reached.

UTILITIES REQUIRED:

Water supply 10 lit/min (approx.)

Drain.

Electricity Supply: 1 Phase, 220 V AC, 3 KW.

Floor area 2 m x 0.6 m

EXPERIMENTAL 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 magnetic pump.

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

counter flow unit.

5. Adjust the flow rate on cold water side between ranges of 1.5 to 4 L/Min.

6. Adjust the flow rate on hot water side, between the rate of 1.5 to 4 L/Min.

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

8. Record the temperatures on hot water and cold water side and also the flow rates

accurately.

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

SPECIFICATION:

Inner Tube : Material = SS, ID = 9.5 mm, OD = 12.7 mmOuter Tube : Material = GI, ID = 28 mm, OD = 33.8 mmLength of the heat Exchanger : L = 1.61 mTemperature Controller : Digital, Range : 0-2000CTemperature Indicator : Digital, Range : 0-2000C & least count 0.10C

with multi channel switch.Temperature Sensors : RTD-PT-100 type. (5 Nos.)Flow measurement : Rotameter (2 Nos.)Water Bath : Material : SS insulated with ceramic wool and

powder coated MS outer Shell fitted with heating elements 3kw (2 Nos., 1.5 kw each).

Pump : FHP magnetic drive pump (Max operating temp. 850C)

FORMULAE:

1. Heat Transfer rate, is calculated as

qh = Heat Transfer rate from hot water.

= mh C p h (T h i – T h o ) K cal / hr.

qc = Heat Transfer rate to the cold water.

= mc C p c (T c o – T c i ) K cal / hr.

q = K Cal/hr.

2. L M T D = logarithmic mean temperature difference which can be calculated as per the following formula:

L M T D = ∆Tm = ∆Ti – ∆T0

In(∆Ti ∆T0)

Where : ∆Ti = ∆Thi - Tci (for parallel flow)= ∆Thi - Tco (for counter flow)

and ∆To = ∆Tho - Tco (for parallel flow)= ∆Tho - Tci (for counter flow)

Note that in a special case of Counter Flow Exchanger exists when the heat capacity rates Cc & Ch are equal, then Thi – Tco = Tho – Tci thereby making ∆Ti

= ∆To. In this case. LMTD is of the form 0/0 and so undefined. But it is obvious that since ∆T is

constant throughout the exchanger, hence

∆Tm = ∆Ti = ∆To

(acc. to ref. Fundamental of Engineering Heat & Mass Transfer by R.C. Sachdeva, Pg.499)

3. Overall heat transfer coefficient can be calculated by using.

q = UA ∆Tm

U =

Calculated Ur i based on Ai = π di L

Ur o based on Ao = π do L

4. Compare the values of ∆Tm & q in the parallel flow and counter flow runs. Note that if experiment is conducted very carefully then the superiority of counter flow arrangement in terms of higher values of Tm and excess values of q for same flow rates condition can be revealed.

OBSERVATION & CALCULATION:

PARALLEL FLOW:S.No Hot water side Cold water side

Flow rate ∆Thi 0C ∆Tho

0C Flow rate ∆Tci 0C ∆Tco

0C12

COUNTER FLOW:

S.No Hot water side Cold water sideFlow rate ∆Thi

0C ∆Tho 0C Flow rate ∆Tci

0C ∆Tco 0C

12

CALCULATIONS:

Ao = π do L = 3.1415 x 12.7 x 10-3 x 161 x 10-2 = 0.0642 m2

CASE I : COUNTER FLOW

Mass flow rate of Hot water:-

Average temp. = ------------ 0C

MH = ------------ kg/hr.

PH = ------------ kg/m3

CpH = ------------ kJ/kg0K

Mass flow rate of cold water

Average temp. = ------------ 0C

Mc = ------------ kg/m

pc = ------------ kg/m3

Cpc = ------------ kJ/kg0K

Heat Flow Rate

QH = MH CpH ∆T = ------------------- kW

Qc = MC CpCH ∆T = ------------------- kW

Effectiveness of HE, ε=

Qactual = = ------------------- kW

Qmax = Mh CPh (Thi - TCi) = ------------------- kW

L.M.T.D. for Counter Flow =

Q = Uo - Aio LMTD

Uo = = ------------------- kW /m2 0C

CASE II : PARALLEL FLOW

Mass flow rate of Hot water :-

Average temp. = --------------- 0C

MH = --------------- kg/hr.

PH = -------------- kg/m3

CpH = -------------- kJ/kg0K

Mass flow rate of cold water

Average temp. = ------------ 0C

Mc = ------------ kg/m

pc = ------------ kg/m3

Cpc = ------------ kJ/kg0K

Heat Flow Rate

QH = Mh CPh ∆T = ------------------- kW

Qc = MC CPc ∆T = ------------------- kW

Effectiveness of HE, ε=

Qactual = = ------------------- kW

Qmax = Mh CPh (Thi - TCi) = ------------------- kW

L.M.T.D. for Counter Flow =

Q = Uo - Aio LMTD

Uo = = ------------------- kW /m2

0C

Nomenclature :

qh = heat loss by the hot water, kW

mh = mass flow rate of the hot water

Cph = specific heat of hot fluid at mean temperature.

Tho = outlet temperature of the hot water

Thi = inlet temperature of the hot water

qc = heat gained by the cold water

mc = mass flow rate of the cold water

Cpc = specific heat of cold fluid at mean temperature

Tco = outlet temperature of the cold water

Tci = inlet temperature of the cold water

q = average heat transfer from the system

U = overall heat transfer coefficient.

Uri = overall heat transfer coefficient of inner pipe

Ai = π di L X-sectional area of inner pipe.

U r o = overall heat transfer coefficient of outer pipe

Ao = π di L X-sectional area of outer pipe.

Precautions and Maintenance Instruction:

1. Use the stabilized A.C. Single Phase supply only.2. Never switch on mains power supply before ensuring that all the ON/Off switches

given on the panel are at OFF position.3. Keep all the assembly undisturbed.4. Never run the apparatus if power supply is less than 180 volts and above than 240

volts.5. Operate selector switch of temperature indicator gently.6. Always keep the apparatus free from dust.7. For parallel flow open the valves V1 & V3 and close valves V2 & V4.

8. For counter flow open the valves V2 & V4 and close valves V1 & V3.9. Don’t 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.

Troubleshooting :

1. If electric panel is not showing the input on the mains light. Check the fuse and also check the main supply.

2. If D.T.I. displays “I” on the screen check the computer socket if loose tight it. 3. If temperature of any sensor is not displays in D.T.I. check the connection and

rectify that.

EXPERIMENT NO: 11

NAME OF EXPERIMENT: SHELL & TUBE HEAT EXCHANGER

OBJECTIVE:To study of heat transfer in Shell and Tube Exchanger.

AIM:To calculate overall heat transfer coefficient for Shell and Tube Exchanger.

INTRODUCTION:Heat exchanger is device 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.

DESCRIPTION:The apparatus consists of Parallel Flow/Counter Flow heat exchangers. The hot fluid is hot water, which is attained from an insulating water bath using a magnetic drive pump and it flow through the inner tube while the cold water flowing through the annuals. For flow measurement Rotameters are provided at inlet of cold water and outlet of hot water line. The Hot water bath is of recycled type with Digital Temperature Controller 0 to 1000C.

UTILITIES REQUERED:Water supply 20lit/min (approx.)Drain.Electricity Supply; 1 Phase, 220 V AC, and 4 kW.Floor area of 1.5m x 0.75 m

EXPERIMENTAL PROCEDURE:

STARTING PROCEDURE:

1. Clean the apparatus and make water bath free from dust.2. Close all the drain valves provided.3. Fill water bath ¾ with clean water and ensure that no foreign particles are there.4. Connect cold water supply to the inlet of cold water Rotameter Line.5. Connect outlet of Cold water from Shell to Drain.6. Ensure that all on/off switches given on the panel are at OFF position.7. Now switch on the main power supply (220 V AC, 50 Hz).8. Switch on heater by operating Rotary Switch given on the panel.9. Set Temperature of the water bath with the help of Digital Temperature Controller.

10. Open flow control valve and By-pass valve for Hot water supply.11. Switch on Magnetic Pump for hot water supply.12. Adjust Hot water flow rate with the help of flow control valve and Rotameter.13. Record the temperatures of Hot and Cold water inlet & outlet when steady state is

achieved.

SHUTDOWN PROCEDURE:

1. When experiment is over, Switch off heater first.2. Switch of Magnetic pump for hot water supply.3. Switch off power supply to panel.4. stop cold water supply with the help of flow control valve.5. Stop hot water supply with the help of flow control valve.6. Drain cold and hot water from the shell with the help of given drain valves.7. Drain water bath with the help of Drain valve.

SPECIFICATION:

1. Shell.

Material = S.S.

Inner dia. = 208 mm

Length = 500mm

25% cut baffles at 100mm distance 4 Nos.

2. Tube Material = S.S.

OD = 16mm

Length of tubes = 500mm

Nos. of tubes = 24

3. Temperature controller = Digital 0-1000C

4. Temperature sensors = RTD PT-100 type ( 4nos.)

5. Temperature indicator = Digital 0 to 2000C with multi-channel switch.

6. Electric heater = 230 V AC 2kW (2 nos.)

7. Flow measurement = Rotameter (2 nos.)

8. Water bath = Material: SS insulated with ceramic wool and powder coated MS outer shell fitted with heating elements.

9. Pump = FHP magnetic drive pump (max.operating temperature 850C)

FORMULAE:

1. Qh = mh Cph ( Thi - Tho ) W 2. Qc = mc Cpc ( Tco - Tci ) W

3. Uo =

4. LMTD = ( ∆Tm ) =

OBSERVATION & CALCULATION:

S.No.

HOT WATER SIDE COLD WATER SIDE

FLOW RATE mh Kg/hr Thi oC Tho

oC FLOW RATE mh

Kg/hrTci

oC TcooC

1.2.3.4.

PRECAUTIONS & MAINTENANCE INSTRUCTIONS:

1. Never switch on main power supply before ensuring that all the on / off switches given on the panel are at off position.

2. Never switch on Heaters before filling water bath ¾ with clean water. It may damage heaters.

3. Never run the pump at low voltage i.e. less than 180 Volts.4. Never fully close the Delivery and By-pass line Valves simultaneously.5. Always keep apparatus free from dust.6. To prevent clogging of moving parts, run pump at least once in a fortnight.7. Frequently Grease / Oil the rotating parts, once in three months.8. Always use clean water.9. If apparatus will not be in use for more than one month, drain the apparatus

completely and fill pump with cutting oil.

TROUBLESHOOTING:

1. If electric panel is not showing the input on the mains light. Check the fuse and also check the main supply.

2. If D.T.I. displays “1” on the screen check the computer socket if loose tight it.3. If temperature of any sensor is not displays in D.T.I. check the connection and

rectify that.4. Voltmeter showing the voltage given to heater but ampere meter does not. Tight

the heater socket & switch if ok it means heater burned.

EXPERIMENT NO: 12

NAME OF EXPERIMENT: RISING FILM EVAPORATOR

(SINGLE EFFECT) (LONG TUBE VERTICAL TYPE)

OBJECTIVE:To concentrate a 5% (wt) sodium carbonate solution to about 15% (wt) solutions.

AIM:To evaluate the following at steady state condition:- Material and heat balance Economy and the capacity of the evaporator. The overall heat transfer coefficient

INTRODUCTION:Evaporation deals with concentration of a non-volatile solute from a solution by the removal of required amount of volatile solvent. Usually the solvent is water. By vaporizing a part of the solvent, useful product i.e. the concentrated solution or thick liquor is produced and the vapor is discarded. Long tube evaporators are usually used for the concentration of foamy liquids. The heat transfer coefficient obtained in a long tube evaporator is less than that obtained in case of a forced circulation evaporator.

THEORY:Material Balance around an evaporator:

Water vapor, Wv

Feed Concentrated liquor Wf W Xf X

Basis: time units

O.M.B. Wf = W + Wv ---------------- (1)

Solute balanceWf Xf = W X ----------------- (2)

M, T2

Wv, tc vapor condenser Heat Balance

M, T1

We, tf Steam condensate Ws, s, We, ts

Neglecting heat losses to the surroundings and negligible heat of dilution. The steady state heat balance around the evaporator is:

Ws λs + Wf hf = Wv H + W h ------------------- (3)

CAPACITY : Evaporator capacity can be defined as: kg. of water evaporated per hour (Wv)

ECONOMY:Steam Economy is defined as: kg. of water evaporated per kg. of steam used.Overall heat transfer coefficient (U):Can be obtained from steady state balance:

Q = Ws λs = U A (ts-t) -------------------- (4)

Factors affecting the overall heat transfer coefficient:

1. Boiling point elevation2. Hydrostatic head in the tubes3. Amount of non- condensable present in the steam and condensing temperature of

steam 4. Liquid viscosity and its velocity5. Dirt factor

DESCRIPTION:The set-up consists of stainless steel surrounded by a stainless steel jacket and fitted with accumulator. Dilute solution is feed to tubes. Steam from a steam generator is supplied to shell to concentrate the dilute feed solution to a desired level. The jacket is fitted with a steam trap and the condensate is collected at the end of trap. The vapours of volatile solvent are condensed in a shell & tube type condenser and the balance non-volatile solute collected in the accumulator is recycled through the evaporator.

UTILITIES REQUIRED:Water supply 5 lit/min (approx.) and drain.Electricity supply : 1phase 220 V AC and 4KW.Required chemicals

EXPERIMENTAL PROCEDURE:The evaporator is operated under atmospheric conditions.

1. Prepare 5%(wt) solution of sodium carbonate in water.2. Start filling the evaporator tubes with this solution and when the tubes are at least half

full, start admitting steam into the steam chest and also start cooling water supply to the condenser.

3. As soon as evaporation starts in the tubes, the liquid level in the boiler section starts decreasing. Starts admitting the fresh feed to make up the decrease in liquid level.

4. The evaporated vapor of evaporator is condensed in the condenser. Condensed vapor is collected in a vessel. Amount of vapor condensed is monitored with time.

5. The cold-water flow rate in the condenser is kept constant throughout and cold-water flow rate and its inlet and outlet temperature are measured.

6. Feed and thick liquor temperature are also recorded with time.7. The concentration of thick liquor is monitored by measuring its density at constant

temperature and the determining the concentration from the calibration curve (concentration V/s density graph should be prepared before the start of experiment.)

8. When the liquid is concentration is maintained at 15%.

SPECIFICATION:

1. Evaporator

Material = SSShell ID = 75mmLength = 900mm

Tubes

Material = SSTube OD = 12.7mmTube ID = 9.5mmNo. of tubes = 4

2. CondenserMaterial = SSShell ID = 108mmLength = 500mm

TubesMaterial = SSTube OD = 12.7mmTube ID = 9.5mmNo. of tubes = 12

3. Steam generatorMaterial = SSCapacity = 25Ltrs.Heater = 4 kW( 2Nos., 2kW each)

4. Temperature sensors.Type = RTD PT – 100 (6 Nos.)

FORMULAE:

1. Q= Ws λs = U A (ts-t)

2. Ws λs + Wf hf = Wv H + W h 3. Wf = W + Wv

OBSERVATION & CALCULATION:

1. Effective heating length = ----- mm2. Diameter = ----- mm3. Number of evaporator tubes. = -----

At steady state record the following:1. Condensate rate, = ------ Ws, kg/s2. Thin liquor flow rate, Wf = ------- kg/s3. Thin liquor temperature, tf = ------- K4. Thick liquor flow rate, W, = ------ kg/s5. Thick liquor temperature, t, = ------ K6. Steam condensing temp, ts , = ------ K7. Cooling water flow rate, M, = ------ kg/s8. Cooling water inlet Temp, T1 = ------ K9. Cooling water outlet Temp, T2 = ------ K10. Thin liquor conc.(feed) mass fraction, xf = -------11. Thick liquor conc., mass fraction, x = -------12. Steam pressure P, kN/m2 = -------13. Evaporation rate, Wv ,kg/s = -------

Using the equations given above, calculate the following at the specified steam pressure

Capacity Steam economy Overall heat transfer coefficient

PRECAUTIONS & MAINTENANCE INSTRUCTIONS:

1. Never switch on mains power supply before ensuring that all the ON/OFF switches given on the panel are at OFF position.

2. Keep all the assembly undisturbed.3. Never run the apparatus if power supply is less than 180 Volts and above than 240

volts.4. Operate selector switch of temperature indicator gently.5. Always keep the apparatus free from dust.6. Don’t 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.

TROUBLE SHOOTING:

1. If electric panel is not showing the input on the mains light. Check the fuse and also check the main supply.

2. If D.T.I. displays “1” on the screen check the computer socket if loose tight it.3. If temperature of any sensor is not displays in D.T.I check the connection and

rectify that.4. Voltmeter showing the voltage given to heater but ampere meter does not. Tight the

heater socket & switch if ok it means heater burned.5. If safety valve is not working at more than 1.5 kg/cm2 just to pull that and some

drops of oil into that.

EXPERIMENT NO: 13

NAME OF EXPERIMENT: HEAT TRANSFER THROUGH AGITATED VESSEL

OBJECTIVE: Study of the heat transfer in a agitated vessel.

AIM:To determine the overall heat transfer co-efficient for various degrees of agitation.

THEORY:Thermal resistance to heat transfer arises due to liquid film on the inside of the vessel wall, the wall thickness and due to film formed on the inside of jacket wall. In addition, the scale formed on either side of the jacket wall shall also effect the overall heat transfer co-eff. The overall heat transfer co-efficient (Ud) based on the inside jacket area is;

1/Ud = 1/Uc + Rd

Where ; neglecting the wall resistance and Rd is the dirt factor

Hj is the inside heat transfer coefficient, hoi is the heat transfer coefficient. For the condensing steam in the jacket hj can be evaluated from Chilton et al correlation for jacketed vessel:

Where, L is the length of the paddle, N is the revolution per sec. D j is the inside dia. of the vessel. All other properties may be evaluated at average fluid temperature and used in consistent units. Hoi for condensing steam can be obtained from Perry’s Hand Book, Rd must also be obtained from the hand book. A straight line results when j factor is plotted on a log-log scale against modified Reynolds No, Re given by:

And

ReHeat transfer area can be calculated by considering the bottom to be a flat plate or can be considering as an elliptical head. For the first case:

Heat transfer area A =

Where z is the height to which liquid is filled in the tank. Rate of heat transfer, Q can be obtained from: Q=Ud A ∆Tm

DESCRIPTION:

The set up consists of jacketed vessel, fitted with a 4 bladed impeller. The tank is fitted with baffles. The water temperature inside the jacket is monitored by a Pt-100 sensor. Steam is jacked is supplied by 25 L boiler fitted with 6kW heater. The whole assembly is made of S.S.

UTILITIES REQUIRED:Water supply 20 lit/min (approx.) and drainElectricity supply 1 phase, 220 V AC, 5 kWFloor area of 1.5m 1.5 m

EXPERIMENTAL PROCEDURE:(1) The vessel is filled with measured quantity of water to such a level that jacket is

below the water level.(2) Record the height of water in the tank (z). Note down the initial temp. of water(3) Set the stirrer speed at the desired level and open the steam valve and feed the

saturated steam at 1.5 bar pressure is then admitted to the jacket.(4) Keep the steam pressure constant throughout(5) Note down the temperature of water in the vessel after every one minute till it starts

boiling and the temperature remains constants(6) Note down the height of water at the time of boiling with the help of a meter rod(7) After the evaporation has taken place for 30 minute, again note down the height(8) Knowing the difference in the two levels, the amount of water evaporated can be

easily calculated.

SPECIFICATION:System : Steam to waterJacketed vessel : Material: stainless steel fitted with 4 nos. baffles dia. 350,

depth 500mm Jacket : Width 25mm, insulated with ceramic wool Helical coil : Material copper, OD 16mm ID 13mm Agitator : Stainless steel Impeller fitted on a shaft coupled to a DC

Motor with thyristor Controlled DC Drive.

Condensate Measurement : Measuring Cylinder & stop watch Water flow measurement : Rota meter

Steam Generator : Made of stainless steel fitted with level gauge, pressure gauge, safety valve,

drain and insulated with ceramic wool & cladding with Aluminium foil.

Heaters : 4 kw Nichrome wire heater (2 Nos., 2kW each)

Control panel comprising of :Digital Temperature Controller: 0 – 200 0C (for Steam Generator)Digital Temperature Indicator: 0 – 200 0C with multi channel switch

Temperature sensors : RTD PT-100 type 6 nos. RPM Indicator : Standard make, Digital, Non contact type.

With standard make on/off switch, Mains Indicator etc.

A good quality painted rigid MS structure is provided to support all the parts.

FORMULAE:

1.

2.

3.

OBSERVATION & CALCULATION:Diameter of jacketed vessel = DjDiameter of Impeller = LHeight of water in vessel = ZWeight of water added = mInitial temp of water =Steam pressure =Temp of condensing steam: Ts

OBSERVATION TABLE:

S.No R.P.S, N Time sec

Temp of water, T ºC

Tb ºC (Ts-Tb)ºC dT/d U

The experiment should be repeated at various values of NU can be obtained by integral of differential method.By integrating method:

By differential method:

At boiling

Where W is the mass of water evaporated, Tb is the boiling temp of water and is the latent heat of vaporization of water.

Plot U vs N and discuss your observations.

PRECAUTION & MAINTENANCE INSTRUCTION:

1) Use the stabilize AC single phase supply

2) Never switch on mains supply before ensuring that all the ON/OFF switches given on the panel are at OFF position.

3) Keep all the assembly undisturbed.4) Never run the apparatus if power is less than 180 volts and above than 240 volts.5) Operate selector switch of temp indicator gently.6) 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.

TROUBLESHOOTING:

1) If electrical panel is not showing the input on the mains light. Check the fuse. 2) If D.T.I displays “1” on the screen check the computer socket if loose tight it.3) If temp of any sensor is not displays in DTI check the connection and rectify that.

EXPERIMENT NO: 14

NAME OF EXPERIMENT: BOILING HEAT TRANSFER

Objective of Experiment

1) To study the pool Boiling Phenomenon

2) To observe the Natural Convection Boiling

3) To observe the Nucleate Boiling

4) To draw the graph of the Boiling curve

Where is heat flux based on heater input?

T2 = Heater surface temp.

TS = Saturation temp of the Liquid %

Limitationi) To obtainable higher heater temp. Liquid other than water such as parafin may

be used

ii) With Water the temp will be always less than 1000C

Procedurei) Charge the Container with required quantity of liquid so that the heater is

completely submerged.

ii) Start the heater with small input observe boiling natural convection.

iii) Increase the heater input for boiling

iv) Start the water circulation.

v) Make observation under steady state.

BOILING HEAT TRANSFER

When heat is, added to a liquid from a submerged solid surface which is at a temperature higher than the saturation temperature of the liquid, it is usual for a part of the liquid to change phase. This charge of phase is called boiling. Boiling is of various types, the type being dependent on the temperature difference between the surface and the liquid. The different types arc indicated in Fig. 1 which illustrates a typical experimental boiling curve obtained in a saturated pool of liquid.

Tin- heat flux supplied 10 the surface is plotted against (TV – T,), the difference between the temperature of the surface and the saturation temperature of the liquid. It is si-en that the boiling curve can be divided into three regions: (I) natural convection region, (II) nucleate boiling region, and (III) 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 the liquid in its vicinity causes the liquid to be superheated. This 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 boiling commences. In this region bubble begin to form at certain locations on the heated surface. Region II consists of two parts. In the first part, IIa, the bubbles formed are very few in number. These bubbles

grow in size, separate from the heated surface and rise to the free surface. In the second part 116, the rate of bubble formation as well as the number of locations where they are formed increase,

With increasing temperature difference, a stage is finally reached when the high bubble formation rate causes them to coalesce and blanket the surface with a vapour film. This is the beginning of region III, namely, film boiling. In the first part of this region, IIIa, the vapor film is unstable film boiling may be occurring on a portion of the heated surface area, while nucleate boiling may be occurring on the remaining area. In the second part, 1116, a stable film covers the entire surface. The temperature difference in this region is of the order of 1000oC and consequently radiative heat transfer across the vapour film is also significant.

It will be observed from Fig. 8,3 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) where n is slightly greater than unity (approximately 1.3). 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 (point A). Beyond this, in region IIIa, in spite of the increasing temperature difference, the heat flux decreases because the thermal resistance to heat flow increases with the formation of a vapour film. The heat flux passes through a minimum. (point-B) at the end of region IIIa. It starts to increase again with (Tw- Ts) only 'when stable film boiling begins and radiation becomes increasingly significant.

It is of interest to note how the temperature of the heating surface changes as the heat flux is steadily increased from zero. Up to the point 'A natural convection of boiling then nucleate boiling occur and the temperature of the heating surface is obtained by reading off the value (Tw- Ts) from the boiling curve and . adding to it the value of T If the heat flux is increased a little beyond the value at A, the temperature of the surface shoots up to the value corresponding to the point C H is apparent from Fig, 8.3 that the surface temperature corresponding to point C is high for some surfaces, it is high enough to cause the material to melt. Thus in many practical situations, it is undesirable to exceed the value of heat flux corresponding to point A. This value is therefore of considerable significance in engineering and is called the critical or peak heat flux.

The discussion so far has been concerned with the various types 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. Thus in order to specify pool boiling occurring in any process, one must state (0 whether the liquid is saturated or sub-cooled, and (if) whether it is in the natural convection, nucleate or film boiling region.

CALCULATIONS .

1) Test surface dia = d = 38.3 mm L = 119 mm

2) Surface Area = π dl = 0.0143 m2

3) Cooling Coil dia = 54 mm

4) Cooling Coil height = 72 mm

5) Pool temp. T 1

6) Surface tea; T2 (TW)

7) Saturation temp - Ts = 100 0C

8) Voltage - Volt

9) Current - AMP

OBSERVATION TABLE:

Sr.No. Voltage

VoltsCurrentAmps

Pool temp.

T1

ºC

Surface temp.

T2

ºC

Water inlet temp.

T3

ºC

Water outletTemp.

T4

ºC

WaterFlow rate

1.

2.

3.

q = V x I A = π dl

qHeat Flux = ---

A

Plot the graph (q/A) v/s T2 – T3

Heat balance

m.cp.Δ T Δ T = T4 – T3

cp = 4174 J/kg k

EXPERIMENT NO: 15

NAME OF EXPERIMENT: STEFAN BOLTZMANN APPARATUS

AIM: To calculate Stefan Boltzmann Constant.

INTRODUCTION

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

Law which states that thermal radiation heat flux or emissive power of a

black surface is proportional to the fourth power of absolute temperature of

the surface and is given by Q/A = eb = σT4 (Kcal/hr.m2.K4)

The constant of proportionality e is called the Stefan Boltzmann Constant

and has the value of: 4.876 x 10-8 Kcal/hr.m2.K4 Or 5.67 W /m2.k4.

The object of this experimental set-up is to measure the value of this

constant by an easy arrangement.

DESCRIPTION

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

plate. The outer surface is enclosed in metal water jacket to heat to some

suitable constant temperature.

Four chromel-alumel thermocouples are attached on mner surface of

hemisphere to measure its mean temperature. The disc, which is mounted

in an insulating Bakelite sleeve, is fitted in a hole drilled in the centre of

base plate. The base of a sleeve is conveniently supported from bottom

side. A chromel-alumel thermocouple is used to measure the temperature

of disc. The thermocouple is mounted on the disc to study the rise of its

temperature.

When the disc is inserted at the bottom of hemisphere, the response of

temperature change of disc with time is used to calculate the Stefan

Boltzmann Constant.

SPECIFICATIONS

1. Hemispherical enclosure dia = 200 mm. Approx.

2. Suitable sized water jacket for hemisphere.

3. Base plate of bakelite = 300 x 300 mm2

4. Sleeve size = 50 mm. Dia. Approx.

5. Test disc. Dia = 20mm.

6. Mass of test disc = 0.0036 Kg. (3.6 gms approx.)

7. Specific heat, S of the test disc = 0.1 Kcal/Kg °C

8. Thermocouple No. T6 for measuring the bath

temperature.

9. No. of thermocouples mounted on hemisphere Tl To T4

2

1. Thermocouple mounted on disc (test disc) T5.

2. Temperature Indicator Digital O.loC Least Count, 0-200oC range and

timer set for 5 sec to display the temperature rise of the disc, for

thermocouple NO.5.

3. Immersion water heater of 2000 watt capacity for hot water.

NOTE: The surface of disc and hemisphere are blackened by using

lamp to make their absorbitivities to be approximately unity.

PROCEDURE

1. Heat the water in the tank by the immersion heater up to a desired

temperature. ( say about 80oC to 900C etc.)

2. The disc is kept open before pouring the hot water in the jacket.

3. The hot water is poured in the water jacket. Allow water till it reaches

the level up to the mark on the tube.

4. The hemispherical enclosure will come to some uniform temperature

T in short time after filling the hot water in the jacket.

5. The disc is now inserted from bottom and its temperature is 'T5'.

6. Note down the rise in temperature of disc at every 5 secs. The

radiation energy falling on 'D' from the enclosure is given by :

E = Ad (Ta)4 ………………………

Where Ad = area of the disc in m2

3

(1)

Ta = Average temperature of the enclosure recorded by the

thermocouples T1 To T4.

The Emissivity of the disc D is assumed to be unity (Black disc).

The radiant energy of disc is emitting into the enclosure will be :

E1= AdσT54 (2)

Net heat input to disc per unit time is given by (1) - (2)

E - E1 = σ Ad ( Ta4 – T54) ... ... ... ... ... . .. (3)

If the disc has mass m and specific heat S then a short time after disc

is inserted.

m.s. (dT/dt)= σAd(Ta4-Ts4) or

σ = m.s.(dT / dt} t = 0 Kcal/hr m2 0 K4 Ad (Ta4 – T54 )

In this equation (dT / dt)t = 0 denotes the rate of rise of temperature of the

disc at the instance when its temperature is T5 and will vary with time. It is

clearly best measured at time t = 0 before heat conducted has any

significant effect.

This is obtained from plot of temperature rise of disc with respect to time

and obtaining its slope at t = 0 when temperature = T5, this will be the

required value of dT / dt at t = O. The thermocouple mounted on disc

(i.e. T5) is to be used for this purpose.

4

Note that the disc with its insulating sleeve is placed quickly in position

and start the time and record the temperature at fixed time intervals. The

process is completed in about 30 second’s time.

Ta=Average temperature in

Ta = Average temperature in

0C = T 1 + T2 + T3 + T4 4

°C = Ta + 273

Temperature of disc at the instant when it is inserted =

(T5) = T5 + 273 in 0K

Temperature time response of the disc

Use the Disc Thermocouple NO.5 on Temperature Indicator and note

down rise at the time interval of 5 seconds.

Time (Sec.) t Temperature (T5) oC 0

5 10 15 20 25 30

Plot the graph of T against t as shown in Fig.

Obtain slope from the graph.

(dT / dt) at t = 0 = oC/Sec. = x 3600 DC/Hr.

Value of σ can be obtained by using (3)

σ = m.s.(dT / dt} t = 0 Kcal/hr m2 0 K4 Ad (Ta4 – T54 )

PRECAUTIONS

1. Before starting the experiment fill the water in the Water bath and

then only switch 'On' the heater.

2. Selector switch, dimmer knob should be used gently.

3. When the experiment is over turn the Heater switch to OFF position.

4. Run the equipment once in a week for better performance.

EXPERIMENT NO: 16

NAME OF EXPERIMENT: THERMAL CONDUCTIVITY OF INSULATING POWDER AIM ;-

To determine the thermal conductivity of insulating powder. ( Material - asbestos powder)

INTRODUCTION

Thermal conductivity is one of the important properties of the materials and its knowledge is require

for analyzing heat conduction problems. physical meaning of thermal conductivity is how quickly heat

passes through a given material. Thus the determination of this property has one of the

considerable engineering significance.

There are various methods of determination of thermal conductivity suitable for different materials.

The present apparatus is suitable for finding out thermal conductivity of materials in powdered from.

SPECIFICATIONS

1)Diameter of Inner Sphere

2)

Diameter of outer sphere

3) Mica Heater

4)2 Amp. open type Dimmerstat.

5)

Insulating Powder - Material

6) Digital Temperature Indicator

7)Digital Voltmeter, 1 No.

8)Digital Ammeter, 1 No.

10cm.

20cm.

Nichrome wire type - 200 watt.

Asbestos.

Range : 0 - 300°C.

Range : 0 - 250 V

Range: 0 - 2 Amp.

DESCRIPTION

The apparatus lS mounted on a sturdy table. It consists of two thin walled

concentric copper spheres. The inner sphere houses the heating coil. Heating coil

is Nichrome wire wound on mica sheet. The insulating powder is packed between

two shells. Power supply to the heater is given through a Dimmerstat and is

measured by a Voltmeter and an Ammeter. Chromel-Alumel thermocouples are

used to measure temperatures. Four thermocouples are embedded on inner sphere

and six thermocouples are embedded on outer sphere. All ten temperatures are

measured on a temperature indicator by operating a selector switch. These

readings enable to find out the thermal conductivity of the insulating powder.

PROCEDURE

1) Put Main Switch 'ON'

2) Apply input (power) by operating Dimmerstat. (Note: The power should not

exceed 40 watts otherwise heater wire is likely to burn)

3) Wait for ~ hour for steady state conditions.

4) Note down the readings in the observation table.

5) Repeat the experiments for different heat input.

6) After experiment is over put Dimmerstat to zero position and make the Main

Switch 'OFF'.

EXPERIMENTS

The value of thermal conductivity of the powder can be calculated by usmg

following equation under steady state condition.

q 4n:Kri - ro (Tin -

Tout) ( ro - ri)

2

OBSERVATION TABLE

n - Radius of inner sphere - 50 mm.

ro - Radius of outer sphere - 100mm.

Sr. Volt- Amm- Inner sphere Temp. Outer sphere Temp. No meter eter

V I Tl T2 T3 T4 T5 T6 T7 T8 T9 TlO

--

CALCULATIONS

1) Average temp. for inner sphere

Tin = Tl + T2 + T3 + T4 4

2) Average temp. for outer sphere

Tout T5 + .............................. + TI0 6

3) Heat input q = V x I watt.

4) Thermal Conductivity

K q ( ro - ri ) 4n ri-ro (Tin - Tout)

3

PRECAUTIONS

1) Selector switch, dimmer knob should be used gently.

2) When the experiment is over turn the dimmer knob to zero position.

3) Run the equipment once in a week for better performance.

4) Do not exceed 40 watt.

JAYPEE UNIVERSITY OF ENGINEERING & TECHNOLOGY, GUNA

Heat Transfer Laboratory Manual 74