Modeling Plain Vacuum Drying by Considering a Dynamic Capillary Pressure

S. Sandoval-Torres, J. Rodríguez-Ramírez and L. L. Méndez-Lagunas

Abstract
A coupled drying model for wood is proposed by introducing a dynamic capillary pressure. The pressures of non-wetting phase, the wetting phase, and the capillary pressure at equilibrium has been considered as non-static; this approach includes a two-scale model. According to numerical results, liquid, water vapor and air dynamics in the chamber have strong interactions with re-homogenization in the surface, controlled by capillary forces. The results at 60–100 bar and 70 °C are discussed. The phenomenological one-dimensional drying model is solved by using the COMSOL’s coefficient form and a global equation format. A good description of drying kinetics, moisture redistribution, and mass fluxes is obtained. A comprehensible transition at the fiber saturation point is well simulated.

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Keywords
wood, vacuum drying, dynamic capillary pressure, COMSOL®