Finite element model for the coupled flow of heat and moisture in soils under atmospheric forcing

The Galerkin weighted residual method has been applied to develop a one-dimensional finite element formulation for the coupled equations of heat and moisture flow in soils. The formulation considers pressure and temperature as the dependent variables and is sufficiently general to accommodate various types of initial and boundary conditions. The specific theoretical postulations made in the light of experimental evidence so far can be readily incorporated into the formulation. The formulation has been coded and successfully implemented. This computer model named VAP1 is interactive and portable. It has been verified for various simple cases of uncoupled moisture and heat flow. The simulated results have been compared with available analytical and numerical solutions for these simple cases. The model has also been verified for a fully coupled nonlinear system. For this case the model results have been compared with the measured data available from laboratory experiments on such a system as well as with the results from a finite difference model. Comparisons with measured data indicate that the model is capable of predicting actual evaporation rates over prolonged time periods with good accuracy. It also predicts the water content and temperature profiles to a fair degree of accuracy. The inconsistencies at advanced stages of drying can be plausibly explained in view of the uncertainty in soil property relationships and the limitations of experimental techniques.