10 - Heat and mass transfer in porous material

Abstract

This chapter reviews the coupled heat and moisture transfer in unsaturated porous media and a generalized coupled model, containing the equations of heat and mass balance, is used to study some representative engineering problems. The model includes both the effects of temperature and moisture and in the case of high-intensity drying, a pressure potential is added. Transport coefficients in the coupled system play an important role and they may be determined either by experimental measurement or through a theoretical derivation. Such determinations are currently very difficult but both are very important. Thus researchers in this field are advised to be prepared to expend considerable effort in this endeavor but it is hoped that future research will improve the speed and accuracy of the determination of the governing transport coefficients. The chapter provides a review of the existing literature on the behavior of coupled heat and moisture transfer in porous materials. For the convenience of mathematical analysis, the following assumptions are made—the materials are homogeneous, isotropic, and non-deformable; gravity effects are neglected; the behavior of the moisture can be described by an equation for the total moisture content, which is the sum of the continuity equation for the liquid phase and the continuity equation for the vapor phase. There is local thermodynamic equilibrium between the moisture and the porous matrix. These coupled equations are applied to the analysis of the moisture migration in stored grain and the drying behavior of the materials.