Drying as an immiscible displacement process with fluid counterflow

Experiments with refractive-indexmatched materials show that evaporation of a liquid from a porous medium produces a modified form of immiscible displacement. In this process the displaced fluid is removed from the pore structure by counterflow in the same pore channels as the displacing fluid. Pressure gradients that arise from fluid flow result in displacement fronts that, unlike conventional displacement fronts, are inherently stable irrespective of the relative viscosities of the fluids. © 1987 The American Physical Society.