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

The periodic hot-wire method is an appropriate means for the determination of the thermal diffusivity alpha and thermal conductivity lambda. A thin pl atinum wire in a sample is heated by a sinusoidal alternating current. The resulting thermal waves penetrate into the surrounding sample. The thermal diffusivity alpha and the thermal conductivity lambda, 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 alpha and lambda the temperature field in the sample is calculated ana lytically under the assumption, that the platinum wire represents a perfect , infinitly extended line heat source. This assumption can only be approach ed and thus measurements must deviate from theory. These deviations were de termined by numerical calculations of the temperature field considering the real geometry of the platinum wire. The measurement accuracy and the optim um frequency range of the periodic hot-wire method has been obtained by com paring the numerically and analytically calculated temperature fields. (C) 1999 Elsevier Science Ltd.