ENT 255 Heat Transfer
Laboratory Module
EXPERIMENT 1
HEAT CONDUCTION
1.0
OBJECTIVES
1.1. To examine the temperature profile along a homogeneous bar and radial of cylinder
by conduction.
1.2. To investigate Fourier’s Law for the linear conduction of heat along a homogeneous
bar
2.0
EQUIPMENT
The equipment comprises two heat-conducting specimens, a multi-section bar for
the examination of linear conduction and a metal disc for radial conduction. A control
panel provides electrical and power digital for display heaters in the specimens as well as
the selector switch for data acquisition system
A small flow of cooling water provides a heat sink at the end of the conducting path in
each specimen.
1
2
3
4
7
5
6
8
9
10
Figure 1: Unit Assembly for Heat Conduction Study Bench
No
1
2
3
4
5
Item
Control Panel
Heater Power Indicator
Heater Power Regulator
Heater Power
Temperature Indicator
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ENT 255 Heat Transfer
Laboratory Module
6
7
8
9
10
Temperature Selector
Main Power Switch
Temperature Sensors
Radial Module
Linear Module
2.1 Specifications
a) Linear Module
Consists of the following sections:
i) Heater Section
Material : Brass
Diameter : 25 mm
ii) Cooler Section
Material : Brass
Diameter : 25 mm
iii) Interchangeable Test Section
- Insulated Test Section with Temperature Sensors Array (Brass)
(Diameter = 25mm, Length = 30 mm)
b) Radial Module
Material : Brass
Diameter : 110 mm
Thickness : 3 mm
c) Instrumentations
Linear module consists of a maximum of 9 temperature sensors at 10 mm interval.
For radial module, 6 temperature sensors at 10 mm interval along the radius are
installed.
Each test modules are installed with 100 Watt heater.
3.0
INTRODUCTION & THEORY
Thermal conduction is the mode of heat transfer, which occurs in a material by
virtue of a temperature gradient. A solid is chosen for the demonstration of pure
conduction since both liquids and gases exhibit excessive convective heat transfer. In a
practical situation, heat conduction occurs in three dimensions, a complexity which often
requires extensive computation to analyze. In the laboratory, a single dimensional
approach is required to demonstrate the basic law that relates rate of heat flow to
temperature gradient and area.
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ENT 255 Heat Transfer
Laboratory Module
3.1 Linear Conduction Heat Transfer
dx
Q
dT
Figure 2: Linear temperature distribution
It is often necessary to evaluate the heat flow through a solid when the flow is not steady
e.g. through the wall of a furnace that is being heated or cooled. To calculate the heat
flow under these conditions it is necessary to find the temperature distribution through the
solid and how the distribution varies with. Using the equipment set-up already described,
it is a simple matter to monitor the temperature profile variation during either a heating or
cooling cycle thus facilitating the study of unsteady state conduction.
THS
kH
kS
kC
THI
TCI
XH
XS
XC
TCS
FiFigure 3: Linear temperature distribution of different materials
Fourier’s Law states that:
Q   kA
dT
dx
(1)
where,
Q = heat flow rate, [W]
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ENT 255 Heat Transfer
Laboratory Module
W 
k = thermal conductivity of the material, 
 Km 
A = cross-sectional area of the conduction, [m2]
dT = changes of temperature between 2 points, [K]
dx = changes of displacement between 2 points, [m]
From continuity the heat flow rate (Q) is the same for each section of the conductor. Also
the thermal conductivity (k) is constant (assuming no change with average temperature of
the material).
Hence,
AH (dT ) AS (dT ) AC (dT )


(dx H )
(dx S )
(dx C )
(2)
i.e. the temperature gradient is inversely proportional to the cross-sectional area.
AC
AH
AC
XH
Q
XS
AC
XC
Figure 4: Temperature distribution with various cross-sectional areas
3.2.
Radial Conduction Heat Transfer (Cylindrical)
Temperature
Distribution
Ti
To
Ri
Ro
Ri
Ro
Figure 5: Radial temperature distribution
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ENT 255 Heat Transfer
Laboratory Module
When the inner and outer surfaces of a thick walled cylinder are each at a uniform
temperature, heat rows radially through the cylinder wall. From continuity considerations
the radial heat flow through successive layers in the wall must be constant if the flow is
steady but since the area of successive layers increases with radius, the temperature
gradient must decrease with radius.
The amount of heat (Q), which is conducted across the cylinder wall per unit time, is:
Q
2Lk (Ti  To )
R
ln o
Ri
(3)
where,
Q = heat flow rate, [W]
L = thickness of the material, [m]
W 
Ro = outer radius, [m]
Ri = inner radius, [m]
k = thermal conductivity of the material, 
 Km 
Ti = inner section temperature, [K]
To = outer section temperature, [K]
4.0
EXPERIMENTAL PROCEDURE
4.1.
Homogeneous bar
1. Make sure that the main switch is initially off. Then Insert a brass conductor
(25mm diameter) section intermediate section into the linear module and clamp
together
2. Connect the ninth sensor (TT1, 2, 3, 4, 5, 6 & 7, 8, 9) leads to the linear module
with the TT1 connected to the end left plug on the linear.
3. Turn ON the water supply and ensure that water is flowing from the free end of the
water pipe to drain. This should be checked at intervals
4. Turn the heater power control knob control panel to the fully anticlockwise position
and connect the sensors leads
5. Switch ON the power supply and main switch, the digital readouts will be
illuminated.
6. Turn the heater power control to 15 Watts and allow sufficient time for a steady
state condition to be achieved before recording the temperature at all nine sensor
points and the input power reading on the wattmeter (Q). Repeat this procedure
for input power at 10 watts and 5 watts. After each change, sufficient time must be
allowed to achieve steady state conditions. Record all your data in Table 1.
7. End of experiment
Note:
i) When assembling the sample between the heater and the cooler take care to match
the shallow shoulders in the housings.
ii) Ensure that the temperature measurement points are aligned along the longitudinal
axis of the unit.
4.2.
Wall of a cylinder
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ENT 255 Heat Transfer
1.
2.
3.
Make sure that the main switch is initially off.
Connect one of the water tubes to the water supply and the other to drain.
Connect the heater supply lead for the radial conduction module into the
power supply socket on the control panel.
Connect the six sensor (TT1, 2, 3 & 7, 8, 9) leads to the radial module, with
the TT1 connected to the innermost plug on the radial. Connect the remaining
five sensor leads to the radial module correspondingly, ending with TT 9
sensor lead at the edge of the radial module
Turn on the water supply and ensure that water is flowing from the free end of
the water pipe to drain. This should be checked at intervals
Turn the heater power control knob control panel to the fully anticlockwise
position.
Switch on the power supply and main switch, the digital readouts will be
illuminated
Turn the heater power control to 15 Watts and allow sufficient time for a
steady state condition to be achieved before recording the temperature at all
six sensor points and the input power reading on the wattmeter (Q). Repeat
this procedure for input power between 10 watts and 5 watts. After each
change, sufficient time must be allowed to achieve steady state conditions.
Record all your data in Table 2
End experiment
4.
5.
6.
7.
8.
9.
5.0.
Laboratory Module
DATA ANALYSIS
Experiment - Homogeneous bar
1). Plot the temperature, T (°C) versus sensor distance, x(meter) in figure 1 from data in
Table 1.
2). From the graph in figure 1 calculate the thermal conductivity at heater power is 5
watts.
Experiment - Wall of a cylinder
1). Plot the temperature, T(°C) versus sensor distance(radius), r (meter) in figure 2 from
data in Table 2.
Name :
______________________________
Date : ______________
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Matrix No :
6.0
Laboratory Module
______________________________
DATA & RESULTS
EXPERIMENT - Homogeneous bar
Table 1
Heater
Power, Q
(Watts)
5
TT1
(°C)
TT2
(°C)
TT3
(°C)
TT4
(°C)
TT5
(°C)
TT6
(°C)
TT7
(°C)
TT8
(°C)
TT9
(°C)
10
15
20
Figure 1
Temperature versus Distance
Name :
______________________________
Date : ______________
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Matrix No :
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_____________________________
EXPERIMENT - Wall of a cylinder
Table 2
Test
A
Heater
Power, Q
(Watts)
5
B
10
C
15
D
20
TT1
(°C)
TT2
(°C)
TT3
(°C)
TT7
(°C)
TT8
(°C)
TT9
(°C)
Figure 2
Temperature(oC) versus radial(x)
Name :
______________________________
Date : ______________
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Matrix No :
Laboratory Module
______________________________
7.0.
DISCUSSION / EVALUATION & QUESTION
7.1.
Briefly summarize the key results of each experiment
7.2.
Explain the significance of your findings
7.3.
Explain any unusual difficulties or problems which may have led to poor results
7.4.
Offer suggestions for how the experimental procedure or design could be
improved.
7.5.
Compare your experimental values with theoretical values given
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ENT 255 Heat Transfer
7.6
Laboratory Module
Define thermal conductivity and explain its significance in heat transfer.
Table 1
Material, k(W/m.K)
Brick (insulating), 0.15
Brick (red), 0.60
Concrete, 0.80
Glass, 0.80
7.7
Refer to Table 1, which would make for better insulation for your home? Explain
your answer
Name :
______________________________
Matrix No :
______________________________
Date : ______________
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ENT 255 Heat Transfer
Laboratory Module
8.0. CONCLUSION
(Based on data and discussion, make your overall conclusion by referring to experiment objective)
The conclusion for this lab is…
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