Numerical analysis of sample dimensions in hot wire thermal conductivity measurements

The parallel hot wire technique has been widely used for experimental measurements of thermal conductivity of ceramic materials. The theoretical model that is used in the fitting procedure assumes that the sample behaves as an infinite medium. The finite dimensions of the actual samples are a source of potential errors. In this work temperature transients in finite samples are numerically simulated and the ones at the measuring point (Mp) are used to calculate thermal conductivities which are compared to the exact values. Consequently, the errors involved, due to the sample finite dimensions can be estimated. Since moving the measuring point further away from the external boundaries of the sample diminishes those errors, the positioning of the temperature sensor is numerically investigated. It is shown that for (r/w)(r=distance from wire to Mp; w=sample width) in the range of 0.2–0.3, the differences in the thermal conductivity values are less than 10%.