Non-stationary heat conduction of a porous medium

The thermal diffusion process is examined for a porous sample with idealized arrangement and form of the pores, when its surface is illuminated by a modulated light. A formula for the frequency dependence of the average surface temperature is derived. It is shown that it depends on the porosity, the form of the pores, and the ratio between a characteristic pore size and the thermal wavelength. In the limiting cases of low frequency of modulation and low porosity the results agree well with those quoted in the literature. The frequency dependence of the surface temperature of a microporous rubber sample, glass filtering crucibles, and leather samples have been measured by a PA cell and compared with the analytical results. The influence of various processes on the heat diffusion in porous media is discussed.