Simultaneous Heat, Mass and Momentum Transfer during Biomass Drying

Abstract

A mathematical model is presented of transport phenomena and moisture evaporation of biofuels exposed to radiative/ convective heating. The medium is considered as a three-phase mixture: virgin solid with bound water to the FSP, capillary water that partially fills the pores, and bubbles containing inert gas and water vapor. Transport phenomena account for convection of capillary water, convection and diffusion of water vapor, surface diffusion of bound water, heat convection and conduction, liquid and gas phase pressure and velocity variations. The partial pressure of vapor is equal to its equilibrium value, which is a function of both temperature and moisture content. The high-temperature (600K) drying of 1 × 10-2m thick particles, with an initial moisture content of 50% on dry basis, has been simulated by varying the external heat transfer coefficient and the permeabilities to liquid and gas flow. The results of the simulations are applied to understand the dynamics of thermal drying and to assess the validity limits of simplified theories of moisture evaporation, usually introduced in the mathematical description of moist particle pyrolysis and gasification.