Analysis of Non-Equilibrium Phase Change in Transfers at Low Water Content by Considering the Film Flow

Analysis of Non-Equilibrium Phase Change in Transfers at Low Water Content by Considering the Film Flow. Abstract: In this study, we analyze the effect of non-equilibrium phase change on transfer at low water content in a sandy soil by considering the contribution of film flow in the motion of liquid water. Indeed, most of the non-equilibrium study methods use for hydraulic conductivity, the van Genuchten-Mualem (VGM) capillary model which does not consider the film flow occurred at low water contents. Thus, we conduct a theoretical study by using an unidirectional non-equilibrium two phase flow model to simulate water transfers by filtration of liquid water and diffusion of water vapour coupled by liquid/gas phase change. We then compare the results of the non-equilibrium with the classical model of VGM for hydraulic conductivity function and another model considering the film flows. The numerical simulation is based on a column of sandy soil exposed to a controlled atmosphere. We observe that the shapes of the profiles of fluxes (liquid water, liquid/vapour non-equilibrium phase change) simulated using the capillary model are very different from those obtained with the model considering the film flow. In this last case, the liquid/gas nonequilibrium is not noticeable as in the case of the capillary model. It seems that the film flows occult the water vapour diffusion by delaying the phase change process, therefore a lower concentration of water vapour into the soil than in the case where the capillary flow alone has been considered.