EFFECTIVE THERMAL CONDUCTIVITY OF Bi-DISPERSED POROUS MEDIA

A unit cell model was used to determine the effective thermal conductivity of bi-dispersed porous media based on the lumped-parameter method. Based on this model, the effective thermal conductivities of these media in the range of solid/fluid conductivity ratio between 0.01 to 10⁵ with different micro- and macro- porosities were predicted. Measurements of effective thermal conductivities of two samples of bi-dispersed porous media (with micro-pore diameter of 80 µm and macro-pore diameters of 200 µm and 400 µm) 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 µm 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.