DRYING TECHNOLOGY, 1 (1), 3-33 (1983-84) DRYING GRANULAR POROUS MEDIA - THEORY AND EXPERIMENT Stephen Whitaker and William T-H. Chou Department of Chemical Engineering University of California Davis, California 95616 U.S.A. Key Words and Phrases: mass transfer, heat transfer, capillary action, evaporation front. ABSTRACT From a general theory of drying granular porous media, we have constructed a simplified theory that consists of a set of coupled, volume-averaged transport equations for the temperature and the saturation. The theory incorporates the liquid and vapor phase con- tinuity equations, combines the liquid, solid and vapor phase thermal energy equations into a single temperature equation and makes use of Darcy's law for the liquid phase to account for moisture trans- port owing to capillary action. By purely qualitative reasoning, one can show that combined heat and mass transfer theories of drying can- not provide a complete theoretical explanation of drying phenomena and a detailed comparison between theory and experiment supports this point of view. Speculation concerning the logical course of subse- quent theoretical studies is provided. INTRODUCTION The motion of both liquid and vapor phase moisture through a rigid, inert, porous solid is described by the governing equations and boundary conditions for mass, momentum and energy. A detailed listing of these governing equations and boundary conditions is 3 Copyright © 1983 by Marcel Dekker, Inc. 0737-3937/83/0 I 0 l'{)003$3.50/0