Investigation on measurement accuracy of the periodic hot-wire method by means of numerical temperature field calculations

Abstract

The periodic hot-wire method is an appropriate means for the determination of the thermal diffusivity a and thermal conductivity λ. A thin platinum wire in a sample is heated by a sinusoidal alternating current. The resulting thermal waves penetrate into the surrounding sample. The thermal diffusivity a and the thermal conductivity λ of the sample can be calculated by analysing the amplitudes and the phase-lags of the waves and applying the Fourier equation. In order to derive the evaluation procedure for a and λ the temperature field in the sample is calculated analytically under the assumption, that the platinum wire represents a perfect, infinitly extended line heat source. This assumption can only be approached and thus measurements must deviate from theory. These deviations were determined by numerical calculations of the temperature field considering the real geometry of the platinum wire. The measurement accuracy and the optimum frequency range of the periodic hot-wire method has been obtained by comparing the numerically and analytically calculated temperature fields.