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-dispers ed porous media with different micro- and macro- porosities were predicted. Measurements of stagnant thermal conductivities of two samples of bi-dispe rsed porous media (with micro-pore diameter of 80 mu m and macro-pore diame ters 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 show n to be in agreement with those based on theoretical predictions. The resul ts indicated that the effective thermal conductivity of a bi-dispersed poro us medium is smaller than that of the mono-dispersed porous medium saturate d 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-d ispersed porous media. (C) 2000 Elsevier Science Ltd.