Modelling and experimental investigation of transient, non-equilibrium mass transfer during steam stripping of a non-aqueous phase liquid in unsaturated porous media

The present paper addresses the one-dimensional unsteady process of steam stripping of the unsaturated zone of soils contaminated with nonaqueous phase liquids (NAPLs). First, the volatilization mechanism and the transport by steam are considered, taking the view that nonequilibrium exists between liquid and vapor phases; second, the effect of evaporation on the specific area is taken into account. The governing equations are rendered dimensionless and solved in closed form. For various dimensionless numbers, solutions are presented, showing the role of the prevailing physical phenomena. Experiments have been performed using two sand mixtures with water and NAPL saturations ranging from 24% to 44% and from 3.8% to 9.4%, respectively. The experimental results confirm the applicability of the theoretical model presented. Furthermore, the analysis results in an empirical correlation for the Sherwood number valid for a broad range of Peclet numbers (2 <Pe <60).