Surface heat and mass transfer coefficients for multiphase porous media transport models with rapid evaporation

Multiphase transport models of food processes require surface heat and mass transfer coefficients as boundary conditions that are traditionally assumed. A conjugate heat and mass transfer model is solved for simple microwave heating of food as a porous medium (from which vapor blows out) with air flow over it, such that there is no need to provide the boundary conditions at the food-air interface. Surface fluxes due to diffusion and flow (blowing) are computed for both vapor and heat from which transfer coefficients are obtained. As evaporation increases with heating, vapor flux due to pressure-driven flow increases but remains small compared with diffusive flux. Vapor accumulation at the interface increases the diffusive flux, leading to an 8% increase in mass transfer coefficient. Heat transfer at the interface occurs through both conduction and flow, and the heat transfer coefficient shows a slight decrease (10%) as blowing increases with heating. The rate of heating has minimal effect on the transfer coefficients. (C) 2011 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.