MULTIPHASE MOISTURE TRANSFER IN POROUS-MEDIA SUBJECTED TO TEMPERATURE-GRADIENT

To describe the history of moisture migration in porous media, the dependence on the relevant material characteristics must be considered. A diffusion theory with a linear or nonlinear coefficient of diffusivity is not adequate for the description of the behavior of mass transfer in a porous medium. Transfers of mass of all phases and the transfer of heat must be considered simultaneously. Based upon the principle of non-equilibrium irreversible thermodynamics, the macroscopic laws of conservation, and the liquid-vapor equilibrium of a porous system, a set of basic equations for simultaneous mass and heat transfer is developed. The developed theory is applied to the investigation of moisture migration in a light-weight concrete wall subjected to a temperature gradient. The result reveals that in addition to diffusion, both the capillary and the evaporation-condensation mechanisms, which are strongly affected by the topology of a porous system, are important in the drying process. © 1979.