Model comparison, thermal nonequilibrium characteristic and boundary conditions discussion of two-phase flow with phase change in porous media

This article comprehensively compares three models of two-phase flow with phase change in porous media: the widely used separated phase model (SPM) and two-phase mixture model (TPMM), and the new developed semi-mixed model (SMM), with the identification of the reasonability of different boundary conditions (BCs) at cold and hot sides. Differences and common features from the physical, as well as from the numerical point of view, are shown in detail. Independent numerical algorithms are, respectively, developed and implemented to solve the three models. The study indicates that the numerical results obtained by SPM and SMM are always similar, but TPMM shows significant difference in temperature and phase distributions of fluid due to the inveracious increase of the effective diffusion coefficient in numerical simulation. The effect of different BCs at cold side emerges and is delivered to the hot side only when the porous matrix is thin, while one type of BC at hot side is infeasible at small porosity. At last, in view of the huge latent heat of phase change, the thermal nonequilibrium characteristic between solid and fluid for two-phase flow is quantitatively evaluated.