A theoretical and experimental study on stagnant thermal conductivity of Bi-dispersed porous media

Based on the unit cell model, stagnant thermal conductivities of bi-dispersed porous media with different micro- and macro- porosities were predicted. Measurements of stagnant thermal conductivities of two samples of bi-dispersed porous media (with micro-pore diameter of 80 mu m and macro-pore diameters of 200 mu m and 400 mu m) saturated with three different fluids (air, FC-72 and water) respectively were conducted. For comparison, the effective thermal conductivity of a mono-dispersed medium with pore diameter of 800 mu m saturated with the same fluid was measured. The measured data are shown to be in agreement with those based on theoretical predictions. The results indicated that the effective thermal conductivity of a bi-dispersed porous medium is smaller than that of the mono-dispersed porous medium saturated with the same fluid because of the contact resistance at micro-scale and higher porosity for bi-dispersed porous media in comparison with the mono-dispersed porous media. (C) 2000 Elsevier Science Ltd.