ABSTRACT
This chapter provides the mathematical development of a model for predicting the duration of the regime of constant flux. During the initial stages of liquid evaporation from a soil, capillarity will tend to maintain a nearly uniform liquid saturation. This results in a constant evaporative flux for a finite period until capillarity can no longer sustain a nearly uniform liquid saturation. Consider semi-infinite sediment medium. Initially it has liquid phase uniformly distributed in it. Mass transport at the surface is limited by external conditions, that is, constant flux exists at the boundary. It is assumed that the apparent effective diffusion of the liquid in the unsaturated sediment be approximately constant during this initial constant flux evaporation stage. The period of constant flux may be assumed to end when the surface concentration becomes zero.
