Thermal Conductivity of Solid Materials

Abstract

Thermo physical properties such as specific heat, thermal conductivity and density are unique for any material. Within a conductive material, thermal conductivity is the main property in the thermal energy transfer. Specific heat and density are the important components involved in the analysis of energy and mass balances. When combining these three properties, we get the thermal diffusivity, which is used in the analysis of unsteady-state heat transfer. Two major methods are used to measure the thermal conductivity of any material. The steady state method named guarded plate method which depends on a constant temperature difference achieved in the specimen of the material. This method needs complicated measurement system, it is unsuitable for the field application [1]. The transient (unsteady-state) techniques generally use a heater of a particular geometry inserted in the sample, and heated within a period of time. These measurement systems are less complex with respect to steady state methods and are better suited for field measurements. The experimental studies for determination of the thermal properties in a transient state has been conducted with numerous methods and techniques. The linear heat source method relies on a steady heat source ,for example, a hot wire, that generate s a temperature field inside an infinite volume of a material. Based on the thermal conductivity of the desired material, the temperature rise in its sample will vary from one material to other. The thermal conductivity, then, can be calculated from the temperature rise at two unique times and the power of the heater. This method was used to measure the thermal conductivity of many solids , fluids and soil [2-4].