Numerical experiments to simulate vertical vapor and liquid water transport in unsaturated non-rigid porous media

Abstract

We present numerical simulations using a model named VALTRAUDE (VApor and Liquid TRansport in Unsaturated DEformable media). It was developed to simulate thermal induced heat and vapor transport and liquid water flow in unsaturated soil as affected by both hydraulic and thermal gradients. Both of the flow phenomena are coupled using the Philip and de Vries [Philip, J.R., de Vries, D.A., 1957. Moisture movement in porous materials under temperature gradients. Trans. Am. Geophys. Union 38 (2), 222–231.] theory. VALTRAUDE is able to consider the porous medium to be non-rigid. We therefore compare numerical simulations of water flow in rigid and non-rigid soil columns under isothermal and non-isothermal conditions. Simulation results indicate that the isothermal steady-state equilibrium pressure head distribution in a soil column under non-isothermal conditions, when the soil column is sealed at the top and at the bottom, so that water content remains constant, is replaced by a dynamic flow equilibrium, where flow of liquid water is balanced by flow of vapor. Thus, in a state of non-isothermal equilibrium, the hydraulic gradient is not zero, and the matric potential at the top of the soil has lower values than under isothermal conditions. Comparing rigid with non-rigid soils, in the case of dry initial conditions and non-isothermal boundary conditions we found smaller flow rates and therefore less negative values of matric potential at the top of the soil. With wet initial conditions, there is nearly no difference between rigid and non-rigid soil.