Abstract
Heat transfer in porous materials is of great importance for various natural, biological and industrial processes. For the large difference between the microscopic and macroscopic dimensions, the volume averaging method (VAM) has been developed to obtain apparent thermal conductivity at the macroscopic level for the microscopic temperature and flow distributions, which can be calculated from the pore-scale simulations. In this article, we perform analysis on the influence of different representative element volume (REV) options on the validity of the thermal equilibrium assumption and the VAM calculated thermal conductivity coefficients. Numerical results from a demonstration simulation are also presented to verify and illustrate the theoretical analysis. Our results and discussion reveal a strong dependence of the thermal equilibrium condition and the calculated conductivity values on REV selection, while this should not be the case since the artificial REV selection should not affect the physical features of a system. This work raises long-time over-looked concerns and calls for caution in future relevant studies.
