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BACKGROUND
Thermal conductivity is the tensor property of a medium which defines its heat conductive efficiency. It also expresses the anisotropy of the medium.1 The heat transfer follows a direct relationship with thermal conductivity and varies accordingly. In general, high thermal conductivity materials are used in heat sink applications, whereas, materials having low thermal conductivity are used as thermal insulation.
The apparatus used for determining the thermal conductivity consists of a central heater sandwiched between a composite structure (Mild Steel, Asbestos, and wood). All the slabs of the different specimen are placed together and are tightened to make a close connection between them. Heater control system is connected to measure and vary the input to the heater. A thermocouple is used to study the temperature at the surface.2
In general, the materials which are a good conductor of electricity, also have excellent thermal conductivity and vice versa. Heat transfer is a universal phenomenon which defines the transmission of energy from one surface to another due to temperature difference or gradient. Heat transfer takes place in both ways; into and out of the system. So, if any material is cooler than other, then heat transfer will take place into it, and in the same way, if it is hotter than other material, then heat transfer will take place out of it.3
The primary objective of this experiment is to determine the thermal conductivity of a composite slab.
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REQUIREMENTS
Slabs: Mild Steel – 0.3m dia. * 0.01m thickness.
Backlite- 0.3m dia. * 0.011m thickness.
Press Wood- 0.3m dia. * 0.0095m thickness.
Heater: Nichrome heater with coil type of 250 Watt capacity.
Thermocouple: Teflon coated, Chromal-Alumal, Yog Electrical Solution
Apparatus: Ammeter
Voltmeter
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PROCEDURE
First of all, adjust the power knob to the zero position by turning in the anticlockwise direction. Switch on the main supply and control unit, and check if the display is lighted up or not. Change the fuse from the control unit box, if the display is not lighted up. Now, check the leakage of electrical current through the apparatus body, and if found, then check the electrical connections and earthing system. After this, press the start button and note down the reading of all eight thermocouples, after 20-30 minutes of giving supply to the heater. Repeat the same process on higher temperature by providing more power to find the average thermal conductivity of the slab.
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CONCLUSION
The process of determining the thermal conductivity of the composite slab has been discussed. Try to keep all the assembly undisturbed during the process, and increase the heater input very slowly.
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REFERENCES
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E. C. Y. I. C. P. Butler, “Thermodynamic and Transport Properties of Gases, Liquids and Solids,” American Society of Mechanical Engineers, vol. 15, no. 3, 1959.
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S. G. I. C. Alexander A. Balandin, “Superior Thermal Conductivity of Single-Layer Graphene,” Material Science and Engineering Program, vol. 8, no. 3, pp. 902-907, 2008.
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J. Y. a. J. Y. Zhang Yinping, “A simple method, the -history method, of determining the heat of fusion, specific heat and thermal conductivity of phase-change materials,” Journal of Measurement Science and Technology, vol. 10, no. 3, 1999.
