Fully Coupled Analysis of Heat, Moisture, and Air Transfer in Unsaturated Soil

This paper presents a new theoretical formulation of coupled heat, moisture, and air transfer in unsaturated soil. A mechanistic approach is adopted that extends a previous potential-based formulation of coupled heat and moisture transfer at constant air pressure. An assessment of the accuracy of the research is presented via comparisons with experimental work for isothermal moisture/air transfer and coupled heat/moisture transfer at constant pressure. Excellent correlation was achieved. Furthermore, verification of the complete new formulation has been achieved by satisfactory comparison of results with those obtained from an independent alternative numerical model. An application of the model to an example test problem is then presented, making use of thermophysical soil parameters that have been independently established for a range of the soil properties specified in the formulation. A number of features of interest related to the interaction between elevated temperatures, induced increased air pressure, and infiltration rates are described. The importance of including the air phase is thus identified, particularly in relation to its effect on the hydration process.