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THERMAL ENGINEERING LAB-II Prepared By: M.VIVEKANANTHAN Page 1
M H L KSHMI
ENGINEERING COLLEGETRICHIRAPPALLI- 621 213
ME2355THERMAL ENGINEERING -II
LABORATORY
LAB MANUAL
MECHANICAL VI SEMESTER
FOR VI SEMESTER B.E. DEGREE COURSE
[REGULATION 2008]
As per the common syllabus prescribed by
ANNA UNIVERSITY, CHENNAI
2012-2013
PREPARED BYMr. M.VIVEKANANTHAN
ASST. PROF / MECHANICAL
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M H L KSHMI
ENGINEERING COLLEGETRICHIRAPPALLI- 621 213
ME2355MECHANICAL ENGINEERING-II
LABORATORY
MASTER RECORD
MECHANICAL -VI SEMESTER
FOR VI SEMESTER B.E. DEGREE COURSE
[REGULATION 2008]
As per the common syllabus prescribed by
ANNA UNIVERSITY, CHENNAI
2012-2013
PREPARED BY
Mr. M.VIVEKANANTHAN
ASST. PROF / MECHANICAL
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CONTENTS
S.NO DATE NAME OF THE EXPERIMENTS PG.NO SIGNATURE
1STEFAN-BOLTZMANN APPARATUS
2TEST ON EMISSIVITY APPARATUS
3
THERMAL CONDUCTIVITY OF POOR
CONDUCTING MATERIAL BY GUARDED
HOT PLATE METHOD
4
HEAT TRANSFER IN NATURAL
CONVECTION
5
HEAT TRANSFER IN FORCED
CONVECTION
6
HEAT TRANSFER FROM A PIN-FIN
APPARATUS BY FORCED CONVECTION
MODE
7
PARALLEL FLOW / COUNTER FLOW HEAT
EXCHANGER
8
PERFORMANCE TEST ON TWO STAGE
RECIPROCATING AIR COMPRESSOR
9
THERMAL CONDUCTIVITY OF
INSULATING
MATERIAL - LAGGED PIPE
10EXPERIMENTS ON AIR-CONDITIONING
SYSTEM
11
PERFORMANCE TEST ON SINGLE/TWO
STAGE RECIPROCATING AIR
COMPRESSOR
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STEFAN-BOLTZMANN APPARATUS
EXP.NO: 01
DATE:
AIM:
To determine the value of Stefan-Boltzmann constant for radiation heat transfer.
THEORY:
Stefan-Boltzmann law states that, the Total emissive power of a perfect black body is
proportional to fourth power of the absolute temperature.
Eb = T4
=5.6697 X 10-8W/m2K
DESCRIPTION OF THE APPARATUS:
The apparatus consists of a flanged copper hemisphere fixed on a flat non-conducting
plate. A test disc made of copper is fixed to the plate. Thus test disc is completely enclosed by
the hemisphere. The outer surface of the hemisphere is enclosed in a vertical water jacket used
to heat the hemisphere to a suitable constant temperature. Three Cr-al thermocouples are
attached at three strategic places on the surface of the hemisphere to obtain the temperature. The
disc is mounted on a Bakelite sleeve which is fitted in a hole drilled at the centre of the base
plate. Other Cr-al thermocouples are fixed to the disc to record its temperature.
SPECIFICATIONS:
Diameter of the disc = 20 mm
Thickness of the disc = 0.5 mm
Mass of the disc (m) = 5 gms
Specific heat of the test disc (Cp) = 380 J/kg-KInner diameter of the hemispherical surface = 200 mm
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OBSERVATION TABLE:
Let TD= T3,Temperature of the disc before inserting into the plate in K = --------------
Sl.no
Hot water temp
T
Sphere top side
tempT1
Sphere left side
tempT2
Sphere right side
tempT4
C K C K C K C K
TEMPERATURE TIME RESPONSES:
SL.NO TIME
Secs
TEMPERATURE
OF DISC in C
T3
TEMPERATURE
OF DISC in K
T3
1
2
3
4
5
6
7
8
9
10
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PROCEDURE:
1. Fill the water in the SS container with immersion heater kept on top of the panel.
2. Remove the test disc before starting the experiment.
3. Heat the water in the SS container to its boiling point.
4. Allow the boiling water into the container kept into the bottom containing copper
hemisphere until it is full and allow sufficient time to attain thermal equilibrium
which is indicated by the three thermocouples provided on the hemisphere.
5. Insert the test disc fixed on the Bakelite sleeve fully in and lock it. Start the
stopwatch simultaneously.
6. Note down the temperature of the disc at an interval of 20 sec for about 5 to 10 min.
CALCULATIONS:
1. Plot the graph of temperature of the disc Vs time and obtain the slope of the line.
2. Average temperature of the hemisphere T avg= (T1+T2+T3 ) / 3 in K
3. Rate of change of heat capacity of the disc = m Cp dT/dt
4. Net energy radiated on the disc = AD( Tavg4TD
4)
Rate of change of heat capacity of the disc = Net energy radiated on the disc
m Cp dT/dt = AD( Tavg4TD
4)
MODEL GRAPH:
Temp in K
Time in sec
RESULT:
Thus the Stefan-Boltzmann constant () of the given specimen is found to be ..
The difference is found to be .
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TEST ON EMISSIVITY APPARATUS
EX.NO: 02
DATE:
AIM:
To measure the emissivity of the test plate surface.
DESCRIPTION OF APPARATUS:
An ideal black surface is one, which absorbs the radiation falling on it. Its reflectivity and
transmissivity is zero. The radiation emitted per unit time per unit area from the surface of the
body is called emissive power.
The experimental sets up consists of two circular aluminum plates identical in size and
are provided with heating coils at the bottom. The plates or mounted on thick asbestos sheet and
kept in an enclosure so as to provide undisturbed natural convection surroundings. The heat input
to the heaters is varied by two regulators and is measured by an ammeter and voltmeter. Thetemperatures of the plates are measured by Iron thermocouples. Each plate is having three
thermocouples; hence an average temperature may be taken. One thermocouple is kept in the
enclosure to read the chamber temperature. One plate is blackened by a layer of enamel black
paint to form the idealized black surface whereas the other plate is the test plate. The heat
dissipation by conduction is same in both cases.
SPECIFICATION :
Diameter of test plate and black surface = 150 mm
PROCEDURE:1) Connect the three pin plug to the 230V, 50Hz, 15 amps main supply and switch on the
unit.
2) Keep the thermocouple selector switch in first position. Keep the toggle switch in
position 1. By operating the energy regulator 1 power will be fed to black plate. Now keep the
toggle switch in position 2 and operate regulator 2 and feed power to the test surface.
3) Turn the thermocouple selector switch clockwise step by step and note down the
temperatures indicated by the temperature indicator from channel 1 to 7.
4) After the experiment is over turn both the energy regulators 1 & 2.
5) For various power inputs repeat the experiment.
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TABULATION:
S.No
Heat input
Black body
Temperature
C
Test Surface
Temperature
C
Chamber
Temperature
T7
Emissivity of
Test Surface
V I Q T1 T2 T3 T4 T5 T6 C
1
2
3
4
EMISSIVITY APPARATUS
CHAMBER
T1 T4 T5
T2 T3 T6 T7
TEST PLATE BLACK PLATE
DIA. - 150 mm DIA. - 150 mm
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CALCULATIONS:
Temperature of Black Surface Tb = (T1+ T2+ T3) / 3 in K
Temperature of Test Surface Tt = (T4+ T5+ T6) / 3 in K
Ambient temperature Ta = (T7+273) in K
Where,
T1, T2, T3, T4, T5 & T6in K
b = Emissivity of the Black Surface = 1
t= Emissivity of the Test Surface
Ab = Area of the Black Surface
At = Area of the Test Surface
Here, At= Ab, Pb= Pt
(Tb4
T74
)
et= ---------------------
(Tt4T7
4)
RESULT:
Emissivity of the Test Surface is found to be ---------------
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THERMAL CONDUCTIVITY OF POOR CONDUCTING MATERIAL BY
GUARDED HOT PLATE METHOD
EX:NO : 03
DATE :
AIM:
To determine the thermal conductivity of a poor conducting material, say asbestos sheet
by guarded hot plate method.
THEORY:
Thermal conductivity is a specific property of any conducting material which is defined
below for a homogeneous solid as the quantity of heat conducted across a unit area normal to the
direction on unit time and for unit temperature gradient along the flow.
K = ( Q dL ) / ( 2A dT )
Where, Q = Heat conducted in watts
dL= Thickness of Plate in m
A = Area of conduction heat transfer in m2
dT = Temperature difference across the length dL in0C
BASIS OF MEASUREMENT:
Experimental measurement of thermal conductivity of solid can be
accomplished by a variety of methods, all based on the observation of the temperature gradient
across a given area of the material conducting heat at a known rate. Each of these methods has
certain unique limitations, and the choice of one over another is governed by the general
temperature level at which K is measured by physical structure of the material in question, andby whether the material is a good or poor conductor.
In measuring the thermal conductivity of poor conductors, the specimens
are taken in the form of sheets in order that the heat flow path be short and the conducting area
large (low dL, higher A)
Guarded hot plate method is generally used to conduct such an
experiment. In this method, electrically heated thermal guards are placed adjacent to the exposed
surface of the source H1, specimen S, and sink H0, these thermal guard plate are independently
maintained at the same temperature as the adjacent surface, to ensure ideally no heat leakage
occurring from source, specimen or the sink boundaries. The enclose drawings given actual
dimensions of various components of the apparatus.
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DESCRIPTION OF APPARATUS:
Enclosed drawing and various specifications associated with all the
components. The test specifications associated with all the components. The test section
assemblies consisting of the asbestos specimen, heaters as well as thermocouples are shown
separately 9 thermocouples are available to measure temperatures of heaters, the two specimens
and the water inlet and outlet. It should be noted that (T3-T4) gives the temperature gradient
across the top asbestos sheet and (T5-T6) gives the corresponding quantity for the bottomspecimen. Provision is also made to measure the cooling water flow rate. The whole assembly is
enclosed in an insulating layer of mineral wool to prevent radiation and connective losses to the
maximum extent possible.
SPECIFICATIONS
Material = Asbestos sheet (commercial grade)
Specimen Diameter, D = 150 mm
Specimen Thickness, L = 12 mm ( 2 pieces, one at the top and one at the bottom )Area of specimen, A = /4 D2Heat input Q = VI watts
Heat input is from two contributions: Main heater and guard heater.
Both these contributions are to be summed up to obtain the total heat that is dissipated by
the heaters. However only half of this heat input will pass (ideally through each of the two
specimens) it may also be noted that since the heaters are sandwiched between 2 layers of
commercial grade asbestos sheet, heat will be dissipated through both the layers. For the purpose
of calculations, average temperature gradient T = [(T3T4) + (T5T6)] / 2is used.
EXPERIMENTAL PROCEDURE:The panels consist of voltmeter, ammeter, and temperature indicator (all digital). Dimmer
controls, volt and ammeter selector (common) switch, thermocouples selector switch and
schematic diagram.
1. Connect the three pin top to 230V, 50 Hz, 5 amps power supply socket, dimmers in OFF
position.
2. Keep the voltmeter and ammeter selector switch in 1 position. Turn the dimmer one in
clockwise and adjust the power input to main heater to any desired value by looking at
the voltmeter and ammeter.
3. Allow the unit to reach steady state. (Anywhere from 20-30 min).
4. Note down the temperature indicated by the digital temperature indicator by turning thethermocouples selector switch clockwise step by step (1,2,3,4,5,6,7,8,9).
5. Repeat the experiment for different power inputs to the heater.
6. Tabulate all the readings and calculate for different conditions.
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OBSERVATION TABLE:
S.No VoltsCurrent
(I)T1 T2 T3 T4 T5 T6 T7 T8 T9
T K
Unit V Amps 0C0
C
0
C
0
C
0
C
0
C
0
C
0
C
0
C
K
W/
mK
1
2
3
4
THERMAL CONDUCTIVITY APPARATUS
T
T T
T T T T
T
GUARD HEATER MAIN HEATER SPECIMEN PLATES
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RESULT:
Thus the thermal conductivity (K) of the asbestos sheet is found to be
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Heat Transfer in Natural ConvectionEX:NO: 04
DATE:
Aim:-
To determine the surface heat transfer co-efficient of a vertical tube losing heat by naturalconvection.
Theory :-
When a hot body is kept in still atmosphere, heat is transferred to the surrounding fluid by natural
convection. The fluid layer in contact with the hot body gets heated; rise up due to the decrease in its
density and the cold fluid rushes in to take place. The process is continuous and the heat transfer takes
place due to the relative motion of hot cold fluid particles.
Applications:-
Transmission lines, pipes, refrigerating coils, hot radiators and buildings etc..
The heat transfer coefficient is given by Newtons law of heating (cooling) :
Experimental Formula , Q = h As ( Ts- T)
Where, h = Average surface heat transfer coefficient (W/ m2 0C)
q = Heat transfer rate (Watts)
As = Area of heat transferring surface = .D.L (m2)
Ts = Average surface temperature
(T1 + T2+ T3 + T4 + T5+ T6+ T7)
TS = ------------------------------------------------0C
7
T8= T= Ambient temperature in the duct = 0C
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The surface heat transfer coefficient, of a system transferring heat by natural convection depends
on the shape, dimensions and orientation of the fluid and the temperature difference between heat
transferring surface and the fluid. The dependence of h on all the above-mentioned parameters is
generally expressed in terms on non-dimensional groups as follow:
h x L
Where, Nu = ----------k
g.L3. . T
Gr = -----------------
v2
Where, L = Length of the pipe (m) T = [Ts T]
K = Thermal conductivity of fluid.
v = Kinematics Viscosity of fluid.
= Coefficient of volumetric expansion for the fluid.
g = Acceleration due to gravity ( 9.81 m/s2)
1
For gases, = ---------------- / 0 k
(Tf+ 273)
(Ts + T)
Tf = ----------------2
For a vertical cylinder losing heat by natural convection,
h x L
Nu = --------- = 0.59(Gr. Pr)0.25
for Gr. Pr < 109, Laminar flow
k
h x L
Nu = --------- = 0.10 (Gr. Pr) 1/3for Gr. Pr > 109 , Turbulent flow
k
L = Length of the cylinder.
All the properties are determined at the mean film temperature (Tf).
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Observations Table:-
S. No. Volt Amp TEMPERATURE,0C
T1 T2 T3 T4 T5 T6 T7 T =T8
1
2
3
4
Schematic Diagram of Free convection heat transfer coefficient apparatus:
Metallic Tube Tc1
2
3
Embedded Heater 4
5
Thermocouples T=T8 6
Rectangular Duct Tc7
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Specification:
1. Diameter of the tube (D) = 40 mm2. Length of tube (L) = 450 mm
Procedure:
1. Note down the specifications of all the instruments provided on the panel and also the
length (L) and diameter (D) of the metallic tube.
2. Switch on the Heater and adjust the heating rate to the suitable level.
3. Wait for some time to ensure the unit to reach steady state.
4. At steady state record the voltage and current readings and the temperatures T1through
T7and T
5. Repeat the experiment for a different heat rate.
Observations
1. O. D. of Cylinder = 40 mm.
2. Length of cylinder = 450 mm.
3. Multichannel Digital Temperature Indicator 0300 0C using Chromel / Alumel thermocouple.
4. Ammeter = Amp. and Voltmeter = Volts.
5. Input to heater Q = V x I Watts.
Result:-
Heat coefficient for a vertical tube losing heat by Natural convection is found to be
h Theoretical = .
hExp = ..
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Heat Transfer in Forced Convection
EX:NO: 05
DATE:
Aim:
To determine the heat transfer co-efficient in forced convection of air in a tube.Introduction:
In many practical situations and equipments, we invariably deal with flow of fluids in
tubes e.g. boiler, super heaters and condensers of a power plant, automobile radiators, water and
air heaters or coolers etc. the knowledge and evolution of forced convection heat transfer
coefficient for fluid flow in tubes is essentially a prerequisite for an optional design of all thermal
system
Convection is the transfer of heat within a fluid by mixing of one portion of fluid with the
other. Convection is possible only in a fluid medium and is directly linked with the transport of
medium itself.
In forced convection, fluid motion is principally produced by some superimposed
velocity field like a fan, blower or a pump; the energy transport is said due toforced convection.
Description:
The apparatus consists of a blower unit fitted with the test pipe. The test section is
surrounded by a Nichrome band heater. Four thermocouples are embedded on the test section
and two thermocouples 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 with cold junction compensation is provided to measure temperatures of
pipe wall at various points in the test section. Airflow is measured with the help of orifice meter
and the water manometer fitted on the board.
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Specification:
Inner diameter (Di) : 25 mm
Length of test section (L) : 400 mm
Blower : 1HP, 3m3/min
Orifice Diameter (D0) : 20 mm
Temperature indicator : Digital type and range 0 - 200 c
Voltmeter : 0 -100 /200v
Ammeter : 02 amp
Heater : Nichrome wire heater wound on
Test Pipe (Band Type) 400 watt
Procedure:
1. Note down all the specifications of the instruments provided on the panel board and the
test section along with the orifice.
2. Start the blower by keeping the valve fully open.
3. Switch on the heater and adjust the heating rate to a suitable level.
4. Allow the system to attain steady state. And note down readings for every 10 min.
5. Record all temperatures, heater input and pressure drop across the orifice.
6. Repeat the experiment at different heat input and air flow rates.
Calculation:
The heat transfer coefficient is given by Newtons law of heating (cooling) :
Experimental Formula, Q = h As ( TbTs)
Where, h = Average surface heat transfer coefficient (W/ m2 0C)
Q = Heat transfer rate, = V x I (Watts)
As = Area of heat transferring surface = .Dt.L (m2)
Ts = Mean surface temperature
Dt= Diameter of the test section = 0.0254 mTb= Bulk Mean temperature
( T2+ T3+ T4 + T5+ T6)
Mean surface temperature, Ts= -----------------------------------0C
5
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(T1+ T7)
Bulk Mean temperature, Tb = ----------------
2
Theoretical Calculation:
Heat input rate = Heat flow rate by air ,
Q = max Cpx ( T1T7)
Where,
Cp=specific heat of air= 1.005 KJ / Kg K
T1= Inlet Temperature of Air in0C
T7= Outlet Temperature of Air in0C
Mass flow rate of air, ma = Cdx Aox a (2gh) / ((Di4D04) / Di4)Where, ma = mass flow rate of air in Kg / sec
Cd = Coefficient of discharge of orifice = 0.68
Ao= Area of Cross Section Orifice in m2= /4 x D0
2
a = density of air at ambient temp. = 1.126 Kg/m3
h = hm[( m / a )1 ]hm= manometer head in meter
m = Density of Mercury = 13600 Kg/m3
ma= U x AiU = Mean Velocity of Flow through tube in m / sec
Ai= Cross Sectional Area of the pipe in m2 = /4 Di
2
Re = Reynolds Number = UxDi/
Where,
= Kinematic Viscosity at Bulk Mean Temperature
Nu = Nusselt Number
h = heat transfer coefficient calculated by using the correlations
Nu = 3.66 For Re 2300 , Turbulant flow
Nu = hxDi/K
Where,
K = thermal conductivity of air at Bulk Mean temp. in w / m k
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Observation Table:
Schematic Diagram:
1) C Channel 2) Motor 3) Blower 4) Adapter6) Orifice 7) Air Inlet Temperature 8) Mica Covered Heater 9) Heater Socket
10) Foam Packing 11) Stainless Still Cladding 12) Monometer
T1:- Air Inlet Temperature ; T6:- Air Outlet Temperature ; T2- T4:- Pipe Wall Temperature
S.
No
Voltage
(V)
(Volts)
Current
(I)
(Amps)
Temperatures
Manometer reading
of water
cm
Air
inlettemp
o
C
Surface temperature
oC
Air
outlettemp
o
CT1 T2 T3 T4 T5 T6 T7 h1 h2 hm
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Result:-
Heat transfer coefficient in forced convection of air in a tube is found to be
h Theoretical = ..
hExp = ..
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Heat Transfer from a Pin-Fin Apparatus by Forced convection mode
EX: NO:06
DATE:
AIM: -
To calculate the heat transfer co-efficient, efficiency and effectiveness of a pin-fin for forced
convection mode.
INTRODUCTION:
Extended surfaces of 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 the surface heat transfer coefficient or the temperature
difference between the surface and the fluid. The use of this is variety of shapes (refer fig. 1).
Circumferential fins around the cylinder of a motor cycle engine and fins attached to condenser tubes of a
refrigerator are a few familiar examples.
It is obvious that a fin surface sticks out from the primary heat transfer surface. The temperature
difference with surrounding fluid will steadily diminish as one move out along the fin. The design of the
fins therefore required knowledge of the temperature distribution in the fin. The main objective of this
experimental set up is to study temperature distribution in a simple pin fin.
APPARATUS:
A brass fin of circular cross section in fitted across a long rectangular duct. The other end of the
duct is connected to the suction side of a blower and the air flows past the fin perpendicular to the axis.
One end of the fin projects outside the duct and is heated by a heater. Temperature at five points along thelength of the fin. The air flow rate is measured by an orifice meter fitted on the delivery side of the
blower.
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SPECIFICATIONS:
1. Duct size (WxB) = 150 mm x 100 mm.
2. Diameter of the fin (Df) = 12 mm.
3. Diameter of the orifice (Do) = 20 mm.
4. Coefficient of discharge Cd = 0.62
5. Centrifugal Blower 1 HP single-phase motor.
6. No. of thermocouples on fin = 5.
(1) to (5) as shown in fig. and indicated on temperature indicator.
7. Thermocouple (6) reads ambient temperature inside of the duct.
8. Thermal conductivity of fin material (Brass) = 110.7 w/m 0C.
9. Temperature indicator = 0300 0C with compensation of ambient temperature up to 500C.
10.Dimmerstat for heat input control 230V, 2 Amps.
11.Heater suitable for mounting at the fin end outside the duct = 400 watts (Band type).
12.Voltmeter = 0100/200 V.
13.Ammeter = 02 Amps.
EXPERIMENTAL PROCEDURE:
Forced Convection: with air circulation (Blower ON)
1. Set the power input to the heater to a desired level through the dimmerstat (VI).
2. Switch on the blower and set the air flow rate to any desired value.
3. Allow the system to attain the steady state.
4. At steady state record the temperatures on the surface (T1, T2, T3, T4, and T5)the ambient
temperature, T6.
5. Note down the difference in level of the two limbs of the manometer.
6. Repeat the experiment by (i) varying the air flow rate and keeping the power input to the
heater constant (ii) varying the power input of the heater and keeping the air flow rate
constant.
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SCHEMATIC DIAGRAM
OBSERVATION TABLE:
S.
No.
V
Volts
I
Amps
Fin Temperatures (0C)
Ambient
Temp.
(0C)
T
Manometer
Reading
in m
T1 T2 T3 T4 T5 T6 h1 h2 hm
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FORMULA USED:
Film Temperature Tf= (Ts+ T)/2 (Property values to be taken at Tf for air)
Average surface temperature Ts= (T1+T2+T3+T4+T5) / 5
Surrounding temperature T=T6
Reynolds number Re=UDeq/
Equivalent diameter Deq= (4 x A)/P
Where, A= Area of duct, WxB (W = Width of the duct in m
B = Breadth of the duct in m)
P = Perimeter of the duct, 2(W+B)
Mean velocity of air in the duct, U = CdAo2g ha and ha= hmm / a
Where , Cd = Coefficient of discharge of orifice=0.62
Ao= Area of orifice, /4 D02
hm= Manometer difference in m
m = Density of Manometer fluid, for mercury=13600 kg/m3
a = Density of Air =1.129 kg/m3
Nusselt Number
NuD= C (ReD)n(Pr)
0.333
Where , NuD= h Df/ K
C and n are taken from the following table
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ReD C n
0.4 - 4.0 0.989 0.33
4 - 40 0.911 0.385
40 - 4000 0.683 0.466
4000 - 40000 0.193 0.618
The fin efficiency is, f = tanh (mL) / mL
The fin effectiveness is, = tanh (mL) / (h Af) / (KbP)
m = h P / kbA
Where, h = heat transfer coefficient W/ m2K
P = perimeter of the fin = D f
Df= Diameter of the fin in m
Af= Area of fin = /4 Df2
Kb= Thermal conductivity of the fin material = 110 W/ m.k
L = Length of the fin in m
T0= Temperature at the base of the fin in0C
T= Surrounding temperature in0C
RESULT :
Thus the value of heat transfer co-efficient under forced condition is determined and also
a) Theoretical value of temperatures along the length of fin.b) Efficiency of the pin-fin for insulated and boundary conditions.
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PARALLEL FLOW / COUNTER FLOW HEAT EXCHANGER
EX.NO: 07
DATE:
AIM:-
To study and compare the heat transfer rate, LMTD, overall heat transfer coefficient and
effectiveness of a heat exchanger working in Parallel flow and counter flow mode.
INTRODUCTION:
Heatexchangersare devices used for effecting the process of heat exchange between two
fluids that are at different temperatures. It is useful in many engineering processes like those in
Refrigeration and Air conditioning system, power system, food processing systems, chemical
reactor and space or aeronautical applications. The necessity for doing this arises in multitude of
industrial applications. Common examples of best exchangers are the radiator of a car, thecondenser at the back of the domestic refrigerator, and the steam boiler of a thermal power plant.
DESCRIPTION & CONSTRUCTION:
The simple example of transfer type of heat exchanger can be in the form of a tube in
tube type arrangement as shown in the figure. One fluid 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. The experiments are conducted by keeping the identical flow rates [approx] while
running the unit as a parallel flow heat exchanger and counter flow exchanger.
The temperatures are measured with the help of the temperature sensor. The readings are
recorded when steady state is reached. The outer tube is provided with adequate insulation to
minimize the heat losses.
The total assembly is supported on a main frame. The apparatus consists of a tube in tube
type concentric tube heat exchanger. The hot fluid is water, which is obtained from the hot water
generator it is attached at the bottom of assembly to supply the hot fluid i.e., water with the help
of pump through the inner tube while the cold fluid is flowing through annulus. Pump set isconnected to the hot water generator to suck the water from it & deliver as per requirement.
Different valves are provided in the system to regulate the flow of fluid to the system. The hot
water & cold water admitted at the same end & the opposite end, named parallel & counter flow
heat exchanger accordingly, is done by valve operation.
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SPECIFICATIONS:
Inner Tube Material : copper
Outer Diameter (do) : 40 mm
Inner Diameter (di ) : 12.5 mm
Outer Tube Material : G.I.
PROCEDURE:
1. Switch on the geyser and wait for some time. Start the flow on hot and cold water sides.
2. Adjust the flow rate on the hot water side to a suitable value, say 700 ml/min and that on
the cold side to 800 ml/min.
3. Keep the same flow rates till steady state condition is reached.
4. Note the inlet and outlet temperatures of the cold and hot fluids.
5. Measure the flow rates of hot and cold fluids.
6. Repeat the experiment for different flow rates as well as for parallel flow and counter
flow modes.
7. Note down the I.D and O.D of the inner and outer tubes and also the length of the
exchanger.
CONSTANT:
Cpc&Cph= Specific heat of cold & hot water = 4.178 kJ / kg K
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OBSERVATION TABLE
PARALLEL FLOW: Parallel Flow, in which fluids flow in the same direction.
Flow rate
mh.
(Kg/s)
TIME TAKEN HOT WATER SIDE COLD WATER SIDE
Hot water Cold water
Inlet Temp.
T1=Thi
( C)
Outlet Temp.
T2=Tho
( C)
Inlet Temp.
T3
( C)
Outlet Temp.
T4
( C)
Counter
flow
Parallelflow
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Calculation for Parallel Flow:
1. Heat transfer rate from hot water, Qh= mhx Cphx (ThiTho) in KJ / sec
2. Heat transfer rate from cold water, Qc= mcx Cpcx (TcoTci)in KJ /sec
3. Qavg= (Qh+ Qc) / 2
(Thi - Tci)(Tho - Tco)
4. LMTD =
ln Thi - Tci
Tho - Tco
5.
Overall heat transfer coefficient Uo can be calculated fromQavg
Uo =
AoLMTD
Where Ao = x do x L (m2)
do = outer diameter of the inner tube in m = 0.0125m
L = length of the heat exchanger in m = 1.5m
6. Cmin= smaller of Ccand Ch
Cc ( Tco-Tci)
7. Effectiveness =Cmin ( Thi-Tci)
Ch ( Thi-Tho)
Cmin ( Thi-Tci)
Cc( Tco-Tci)
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RESULT:
PARALLEL FLOW COUNTER FLOW
The heat transfer rate in W
LMTD
Effectiveness
The heat transfer efficiency =
The fin efficiency =
The fin effectiveness =
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THERMAL ENGINEERING LAB-II Prepared By: M.VIVEKANANTHAN Page 33
PERFORMANCE TEST ON TWO STAGE RECIPROCATING AIR
COMPRESSOR
Ex:No: 08
Date
AIM:
To conduct the performance test on a two stage reciprocating air compressor and to draw
the following graphs:
Delivery pressure Vs Volumetric efficiency
Delivery pressure Vs Isothermal efficiency
Delivery pressure Vs Adiabatic efficiency
APPARATUS REQUIRED:
Stop WatchTachometer
SPECIFICATION:
Make : CEC
Max. Delivery Pressure : 12 bar
Diameter of Low Pressure Cylinder DLP : 70 mm
Stroke Length of Low Pressure Cylinder LLP: 85 mm
Diameter of High Pressure Cylinder DHP : 50 mmStroke Length of High Pressure Cylinder LHp: 85 mm
Coefficient of discharge of orifice : 0.62
Diameter of orifice D0 : 15 mm
Rated speed of compressor : 700 rpm
Energy Meter Constant : 1600 impulse / kW hr
DESCRIPTION:
The two stage air compressor is a reciprocating type (driven by a AC Motor primemover) through a belt. The test rig consists of a base on which the tank (air reservoir) is
mounted. The outlet of the air compressor is connected to the reservoir. The temperature and
pressure of the compressed is indicated by a temperature and pressure gauge. A pressure switchis provided for additional safety. A manometer is provided for measuring pressure difference
across the orifice. The input to the motor is recorded by energy meter.
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PROCEDURE:
1) Check the manometer connections (fill the manometer with water upto half level)
2) Start the compressor.
3) Close the outlet valve and observe the slowly developing pressure.
4) Slightly ahead of the desired pressure, open and adjust the outlet valves so that the
pressure is maintained constant.
5) Note down the readings for different delivery pressures.
CALCULATION:
Theoretical Volume (Vt):
Vs= Vt= ( DLP2LLPN) / 4 x 60
Where, Diameter of Low Pressure Cylinder DLP : 70 mm
Stroke Length of Low Pressure Cylinder LLP: 85 mm
N = Speed of Compressor in rpm
Head (H):
H = h (w/ a)
Where, h = manometer difference (h1h2) in m
w = Density of water = 1000 Kg/m3
a = Density of air = 1.293 Kg/m3
Actual Volume (Va):
Va= CdAo 2 g H
Where, Cd = Coefficient of discharge of orifice = 0.62
Ao= Area of orifice in m2= D0
2/4
g = Acceleration due to gravity (9.81 m/s2)
Volumetric Efficiency (Vol):
Va
Vol = x 100Vt
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Actual Work :
Actual work = (No. of Impulse x 3600 x 0.8) / (Time x E.M.C)Where,
No of Impulse = 10
E.M.C = 1600 imp / kW hr
Isothermal Work :
Isothermal work = PaValn (P3/ P1)Where,
P1= Suction Pressure in N/ m2
P3= Delivery Pressure in N/ m2= Pguage+ Patm
Isothermal Efficiency (Isothermal) :
Isothermal= (Isothermal Work / Actual Work)
Isentropic Work (or) Adiabatic Work :
Isentropic Work = P1V1 + P2V2
Where, = 1.4
V1= VLP= ( DLP2LLP) / 4 ; V2= VHP= ( DHP
2LHP) / 4
P2= P1P3
Adiabatic Efficiency (Adiabatic):
Adiabatic = (Adiabatic Work / Actual Work )
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OBSERVATIN TABLE:
S.
NOReceiver
pressure
Mano
meter
Reading
Speed
Time taken
for 3sec of
energy meter
Temperature in CVol.
Efficiency
%
Isothermal
Efficiency %
Adiabatic
Efficiency %
Bar h1 h2 rpm T1 T2 T3 T4 T5 Vol Isothermal Adiabatic
1
2
3
4
5
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RESULT:
Thus the performance test on a two stage reciprocating air compressor was done and
the following graphs were drawn.
Delivery pressure Vs Volumetric efficiency
Delivery pressure Vs Isothermal efficiencyDelivery pressure Vs Adiabatic efficiency
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THERMAL ENGINEERING LAB-II Prepared By: M.VIVEKANANTHAN Page 38
THERMAL CONDUCTIVITY OF INSULATING
MATERIAL - LAGGED PIPEEX.NO:09
DATE:
AIM :
To find the thermal conductivity of different insulating materials.
DESCRIPTION OF APPARATUS :
The insulator is a material, which retards the heat flow with reasonable effectiveness.
Heat is transferred through insulation by conduction, convection and radiation or by the
combination of these three.
The experimental set up in which the heat is transferred through insulation by
conduction is under study.
The apparatus consisting of a rod heater with asbestos lagging. The assembly is inside
an MS pipe. Between the asbestos lagging and MS pipe saw dust is filled. The set up as
shown in the figure. Let r1 be the radius of the heater, r2 be the radius of the heater with
asbestos lagging and r3be the inner radius of the outer MS pipe.
Now the heat flow through the lagging materials is given by
Q = K12 L ( t) / (ln (r2)/r1) or
= K22 L( t) / (ln(r3)/r2)
Where t is the temperature difference across the lagging.
K1is the thermal conductivity of asbestos lagging material and
K2is the thermal conductivity of saw dust.
L is the length of the cylinder.
Knowing the thermal conductivity of one lagging material the thermal conductivity of the
other insulating material can be found.
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TABULATION :
Heat inputTemperature at Diameter
(D1)0C
Temperature at Diameter
(D2)0C
Temperature atDiameter (D3)
0C
V IVI
Volts
T1T2 T3 T4
T5 T6 T7T8 T9
LAGGED PIPE
SAW DUST
ASBESTOS
T1 HEATER T3
ASBESTOST4 T5 T6
SAW DUSTT7 T8
T4 T1 T7 T5 T8 T6 T3
d1 - HEATER DIA = 20 mm d2 - HEATER WITH ASBESTOS DIA = 40 mm d3 - ASBESTOS & SAW
DUST DIA = 80 mm LENGTH = 500mm
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SPECIFICATION:
Diameter of heater rod, d1 = 50 mm
Diameter of heater rod with asbestos lagging, d2 = 100 mm
Diameter of heater with asbestos lagging and saw dust, d3 = 150 mm
The effective length of the cylinder = 600 mm
PROCEDURE:
1. Switch on the unit and check if all channels of temperature indicator showing proper
temperature.
2. Switch on the heater using the regulator and keep the power input at some particular
value.
3. Allow the unit to stabilize for about 20 to 30 minutes. Now note down the ammeter,
voltmeter readings the product of which give heat input.
4. Temperatures 1, 2 and 3 are the temperature of heater rod, 4, 5 and 6 are the
temperatures on the asbestos layer, 7 and 8 are temperatures on the saw dust lagging.
5. The average temperature of each cylinder is taken for calculation. The temperatures
are measured by thermocouple (Fe/Ko) with multi point digital temperature indicator.
6. The experiment may be repeated for different heat inputs.
The readings are tabulated as below:
CALCULATIONS :
Lagged Pipe:
Avg. Temp. of heater = T1+T2+T3/ 3 = oC
Avg. Temp. of Asbestos lagging = T4+ T5+ T6/ 3 = oC
Avg. Temp. of sawdust lagging = T7+ T8+T9/ 3 = oC
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The heat flow from heater to outer surface of asbestos lagging =
Q = k12 l ( t2-t3) / ln (r3/ r2)
k1 = Thermal conductivity of asbestos lagging, from data look at------------------oC
(average temp of asbestos lagging)
= W/m K.
r2 = Radius of the asbestos lagging = 25 mm
r1 = Radius of the heater = 50 mm
L = Length of the heater = 75 mm
Substituting these values
RESULT :
Thermal conductivity of
(i) Asbestos---------------W/mK
(ii) Sawdust----------------W/mK
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