UNSTEADY OVERALL THERMAL RESISTANCES RELATED TO HEAT CONDUCTION FOR POROUS MEDIA HAVING HIGH BIOT NUMBERS

This study examines the means of determining the unsteady overall heat transfer coefficients for porous media with high Biot numbers. Changes in temperature during the cooling process are estimated using numerical simulations. In addition, the unsteady volume averaged internal thermal resistance values related to heat conduction in porous materials are obtained over the range of thermal conductivity ratios from 0.01 to 1000. A novel formula for calculation of the volume averaged internal thermal resistance for porous materials is devised as the functions of the Biot number and the Fourier number. This model is validated by comparing the outlet temperatures obtained using numerical simulations. The superiority of this newly developed model is also confirmed by comparison with a conventional approach. The new model can reproduce the unsteady temperature development in porous media having Biot numbers ranging from 0.01 to 100. It shows that this newly developed model can be applied in a wider range of Biot numbers than the conventional approach.