Experimental study and modelling of the water phase change kinetics in soils

Summary When dealing with porous media, the liquid‐gas phase‐change is generally considered instantaneous, while a retardation time is observed in the case of hygroscopic soils. So far, little research has been done to characterize the non‐equilibrium behaviour of water phase change. Therefore, we propose a macroscopic model of the liquid‐gas phase‐change rate in porous media, based on the difference of chemical potentials between the liquid and its vapour, which is taken as the driving force. It introduces a phenomenological coefficient that must be determined experimentally. An original experiment able to create a macroscopic non‐equilibrium between the liquid and its vapour is described. Analysing the return to equilibrium leads to the determination of the phenomenological phase‐change coefficient. Depending on the range of partial vapour pressure, two different behaviours are observed: a linear domain close to equilibrium and a non‐linear one far from equilibrium. The results emphasize the relation between water retention properties in hygroscopic porous media and these phase‐change characteristics.