Thermal Conductivity of Composite Slab: Vishwakarma Institute Technology, Pune of

Bansilal Ramnath Agarwal Charitable Trust’s
Vishwakarma Institute Technology, Pune of
(2)
THERMAL CONDUCTIVITY OF
COMPOSITE SLAB
Department of Mechanical Engineering Heat Transfer Lab

Name: Hussain Magar Roll No: 12 Div: C Batch: 1

Sem: 5 AY:
Date of conduction: Date of submission:
Experiment No. 2
TITLE: THERMAL CONDUCTIVITY OF COMPOSITE SLAB
AIM: To determine thermal conductivity and thermal resistance of composite slab.
Apparatus/Instrumentation: Ammeter, Voltmeter, Dimmerstat, Thermocouples, Digital

Temperature Indicator etc.
INTRODUCTION:
Thermal conductivity is the physical property of the material denoting the ease with which a
particular substance can accomplish the transmission of the thermal energy by molecular motion.
Every material resists the flow of heat due to the lattice structure and hence it has its own thermal
conductivity or thermal resistance. In any application of a thermal system the thermal
conductivity or the thermal resistance of the composite material is different as compared to
single material of same dimensions. Hence by keeping the same dimensions of material different
material can be used to reduce/increase the heat transfer rate. This experiment therefore aims to
determine thermal conductivity of a composite slab of different material and of same dimensions.
EXPERIMENTAL ANALYSIS
A. Experimental set-up:
The apparatus consists of central heater sand witched between two aluminum plates. Three types
of slabs are provided on both sides of heater, which forms a composite structure. A small hand
press is provided to remove air gap and ensure the perfect contact between slabs. A dimmerstat is
provided for varying the input to the heater and measurement of input is carried out by using
voltmeter and ammeter readings. Thermocouples are embedded between interfaces of the slabs,
to read the temperatures at the surfaces. The composite structure is placed inside enclosed
chamber.

B. Theory:
Experimental analysis is based on the following assumptions,
Assumptions:
 Individual slab material is isotropic and homogeneous.
 Thermal conductivity is constant in space.
 One dimensional heat conduction.
 Steady state conduction.
 No radiation and convection effects.
Now consider the transfer of heat by conduction through each slab in upward and downward
directions.
Let,
L = Thickness of slab, m
Ti = Average temperature of inner surface of slab (oC)
To = Average temperature of outer surface of slab (oC)
A = Cross-sectional area of plate
K = Thermal conductivity of slab (W/mK)
b1= thickness of M.S. slab
b2= thickness of press wood slab
b3= thickness of backelite slab
Rth1= resistance of M.S slab
Rth2= resistance of press wood slab
Rth3= resistance of backelite slab
Q = Power supplied
According to Fourier law of heat conduction, the heat transfer rate for a slab can be determined
as:
 T  To 
Q i
 L 
 
 KA 
Q = (V x I)
Ta = T7
Tb = (T1+T2)/2
Tc = (T3+T4)/2
Td = (T5+T6)/2

Thermal Conductivity of Composite Slab;
Ksteel = Q.b1 . ……………………….[ A = Π/4 D2]
A x 2 x (Ta -Tb)
K pressed wood = Q.b2 .
A x 2 x (Tb-Tc)
K bakelite= Q.b3 .
A x 2 x (Tc-Td)
Verification of Electrical Analogy:
R1 = b1 .
Ksteel A
R2 = b2 .
K pressed wood A
R3 = b3 .
K Bakelite A
R slab = R1+R2+R3 Theoretical value by an Electrical Analogy
R slab = (Ta - Td)/Q Experimental values
K slab = (b)/A x Rslab Theoretical value by an Electrical Analogy
K slab = Q x b
A (Ta-Td) Experimental values
C.
D. Procedure:
1. See that plates are symmetrically arranged on both sides of heater plates
2. Operate the hand press properly to ensure perfect contact between the plates.
3. Close the box by cover sheet to achieve steady environmental conditions.
4. Switch on the main supply
5. Switch on the heater and adjust the input by dimmerstat for desired heat input.
6. Note down the readings of all thermocouples through selector switch, voltmeter and
ammeter at an interval of 10 minutes until the steady state is reached.
7. Note down the steady state readings.
Technical Specifications:

1. Diameter of all plates 150 mm
2. Thickness of slab, b = b1+b2+b3
3. Thickness of M.S. plate, b1 = 15 mm
4. Thickness of Bakelite plate, b2 = 12 mm
5. Thickness of Pressed wood plate, b3 = 12mm
Observation Table:
Sr. Heater Input Thermocouple Readings, oC
No
V (Volt) I (amp) T1 T2 T3 T4 T5 T6 T7
1 74 0.54 266 260 163 145 122 122 284
2
3
4
Result Table
Sr. No. R slab R slab K slab K slab
(Practical) (Theoretical) (Practical) (Theoretical)
1. 8.108 8.0547 0.272 0.282
2.
3.
GRAPH:
Show variation of temperature along the length of slab.
CALCULATIONS:
Use equations explained above in theory to calculate the thermal conductivity of composite slab.


CONCLUSION WITH SUPPORTIVE JUSTIFICATION:

 Thermal conductivity of composite slab is, k = 0.272 W/m0C.
 Thermal resistance of the composite slab is 8.108 0C/W.
Experimental set-up:
Fig (1), Composite Slab with Coil placed at centre.

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Bansilal Ramnath Agarwal Charitable Trust’s

Vishwakarma Institute Technology, Pune of

Department of Mechanical Engineering Heat Transfer Lab

Name: Hussain Magar Roll No: 12 Div: C Batch: 1

TITLE: THERMAL CONDUCTIVITY OF COMPOSITE SLAB

AIM: To determine thermal conductivity and thermal resistance of composite slab.

Apparatus/Instrumentation: Ammeter, Voltmeter, Dimmerstat, Thermocouples, Digital

Department of Mechanical Engineering Heat Transfer Lab

Department of Mechanical Engineering Heat Transfer Lab

Department of Mechanical Engineering Heat Transfer Lab

Department of Mechanical Engineering Heat Transfer Lab

Department of Mechanical Engineering Heat Transfer Lab

CONCLUSION WITH SUPPORTIVE JUSTIFICATION:

Fig (1), Composite Slab with Coil placed at centre.

Department of Mechanical Engineering Heat Transfer Lab

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