Thermal conductivity measurements for the separation of heat and mass diffusion in moist porous materials
A new experimental procedure for the determination of the thermal conductivity of moist porous materials is presented. The technique, based on a series of successive thermal conductivity measurements with a guarded-hot-plate or a heat-flow-meter apparatus, allows the elimination of the influence of the moisture movement as well as of the moisture distribution on heat transfer inside the sample. A series of measurements on a calcium silicate fibre board is presented. The results enable the separation of different heat transfer modes. The time dependence of the apparent thermal conductivity shows the thermal effects of the moisture rearrangement. At steady-state conditions with respect to heat conduction and moisture movement, the influences of the nonuniform moisture distribution and of the internal moisture circulation were eliminated. That was made possible by the measurement of the apparent thermal conductivity with different temperature gradients and the extrapolation of the results to zero temperature gradient.