Abstract
A thermodynamic energy “water potential” based on the principles of chemical potential of an element of mixed gas is defined as the driving force of gaseous phase water transfer. Adhesive power or “capillary action” and a portion of the water potential, is confirmed as the driving force of liquid phase water transfer. A numerical model of combined heat and water transfer using the water potential is introduced and influences of forces such as gravity and pressure on water transfer are incorporated from the viewpoint of thermodynamics. A way to estimate diffusivities of gaseous and liquid phase water through porous materials and the thermodynamic relations between such diffusivities and the potential are also shown. Accuracy of the numerical model is demonstrated through a comparison between calculation and experiment for different temperature gradients and water content in a porous material.