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A TEMPERATURE WAVE TECHNIQUE FOR SIMULTANEOUS MEASUREMENT OF THERMAL DIFFUSIVITY, CONDUCTIVITY AND CONTACT RESISTANCE OF POROUS MEDIA

M. Bierer
Institut fur Thermodynamik und Warmetechnik Universitat Stuttgart, Pfaffenwaldring 6, D-7000 Stuttgart, FRG

A. Erhard
Institut fur Thermodynamik und Warmetechnik Universitat Stuttgart, Pfaffenwaldring 6, D-7000 Stuttgart, FRG

Erich Hahne
Institut fur Thermodynamik und Warmetechnik, Universitat Stuttgart, 70550 Stuttgart, Germany

Abstract

The proposed measurement technique is based on applying a sinusoidal temperature wave to a layer of a porous medium. Monitoring the decrement and velocity of the intruding wave enables the determination of thermal diffusivity (a). Because data on the temperature amplitudes and phases are obtained, an internal checking of the results is possible.
A least squares fit of the maximum amplitudes at several measurement points leads to an exponential decrement-curve. By extrapolating this curve, the surface temperature can be calculated and compared with the measured one. Thus a temperature leap may be found. The contact resistance between the surface and the porous medium can be calculated from the existing temperature leap.
By implementing a reference layer with known thermo-physical properties in front of the porous medium as an indicator for the entering heat flow a value for the heat-absorption coefficient (b) can be obtained. Thus the calculation of the thermal conductivity from (a) and (b) is possible.

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