Thermal Conductivity

Topics: Heat, Heat transfer, Temperature Pages: 3 (752 words) Published: February 26, 2009
SUMMARY

Heat is normally conducted by atoms literally bumping into each other and in metals electrons also add to this flow of heat, which is why metals tend to be good conductors of heat. The measure of how good a material is at conducting heat is known as its thermal conductivity. Thermal conductivity is defined as the rate at which heat flows through a certain area of a Object of the experiment is to determine the thermal conductivity of metals and insulation body.materials and also to demonstrate that heat flow is directly proportional to temperature differences between faces and to cross sectional area.

Thermal conductivity is defined as:

k = (Q/A) / (ΔT/ΔL) ( Fourier’s equation)

where Q is the amount of heat passing through a cross section, A, and causing a temperature difference, ΔT, over a distance of ΔL. Q / A is therefore the heat flux which is causing the thermal gradient, ΔT / ΔL.

The measurement of thermal conductivity, therefore, always involves the measurement of the heat flux and temperature difference. The difficulty of the measurement is always associated with the heat flux measurement. Where the measurement of the heat flux is done directly (for example, by measuring the electrical power going into the heater), the measurement is called absolute. Where the flux measurement is done indirectly (by comparison), the method is called comparative.

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The apparatus consist of a self clamping specimen stack assembly with electrically heated, calorimeter base, dawar vessel enclosure to ensure negligible loss of heat, and constant heat cooling water supply tank. A multipoint thermocouple switch is mounted on the steel cabinet base and two mercury glass thermometers are provided for water inlet and outlet temperatures readings. Four NiCr/NiAl thermocouples are fitted and connections are provided for a suitable potentiometer instrument to give...