Internal heat transfer coefficients in microporous media with rarefaction effects

The internal heat transfer of different gases in microporous media was investigated experimentally and numerically. The experimental test section had a sintered bronze porous media with average particle diameters from 11 mu m to 225 mu m. The Knudsen numbers at the average inlet and outlet pressures of each test section varied from 0.0006 to 0.13 with porosities from 0.16 to 0.38. The particle-to-fluid heat transfer coefficients of air, CO2 and helium in the microporous media were determined experimentally. The results show that the Nusselt numbers for the internal heat transfer in the microporous media decrease with decreasing the particle diameter, d (p), and increasing Knudsen number for the same Reynolds number. For Kn > 0.01, the rarefaction affects the internal heat transfer in the microporous media. A Nusselt number correlation was developed that includes the influence of rarefaction. The computational fluid dynamics (CFD) numerical simulation was carried out to do the pore scale simulation of internal heat transfer in the microporous media considering the rarefaction effect. Pore scale three-dimensional numerical simulations were also used to predict the particle-to-fluid heat transfer coefficients. The numerical results without slip-flow and temperature jump effects for Kn < 0.01 corresponded well with the experimental data. The numerical results with slip-flow and temperature jump effects for 0.01 < Kn < 0.13 are lower than the numerical results without rarefaction effects, but closer to the experimental data. The numerical results with rarefaction effects can accurately simulate the unsteady heat transfer in the microporous media.