Modelling fully coupled moisture, air and heat transfer in unsaturated soils

A theoretical model has been proposed to describe fully coupled moisture, air and heat transfer in unsaturated soils. Pore liquid water and pore air transfer were assumed to be governed by Darcy’s law and pore water vapour transfer was considered to occur due to two effects, first, under molecular diffusion and, second, as part of the bulk flow of the pore air. The pore water vapour transfer due to the molecular diffusion was described using Fick’s law. Heat transfer was formulated to include effects of conduction, convection and latent heat of vapourization. A three dimensional computer program has been developed to incorporate the proposed model for analyzing the transient coupled flow of moisture, air and heat in unsaturated soils. Both the fundamental mathematical formulation and the computer code have been verified by comparing numerical results with test measurements of a drying sand column.