A receding evaporative front model for the drying characteristics of a flat plate III: pressure and moisture distributions

Abstract

A composite model is presented for the pressure and moisture distributions during a three-stage drying process of a flat plate with a fixed base. In the first stage (saturated stage), the body is fully saturated and capillary flow prevails. During the second stage (partially saturated stage), the evaporative front recedes through the material and divides it into saturated and unsaturated regions. The saturated part of the body is modelled using Darcy\'s Law for pressure-driven flow, while the unsaturated part is characterized by a Fickian diffusion equation, where the pressure model and the diffusion model are coupled through the receding evaporative front. In the third stage (fully unsaturated stage), the saturated region of the partially saturated stage is obliterated and the body is entirely unsaturated. It is shown that the critical point can occur in either the partially saturated stage or the fully unsaturated stage, depending upon the evaporation rate and other parameters of the drying process; both the pressure in the liquid and the moisture concentration of the body increase with distance from the drying face at any given time.

Keywords: drying, pressure, moisture, distribution, flat plate

Global Journal of Engineering Research Vol.4 (1&2) 2005: 49-61