Numerical Simulation Of Heat And Mass Transfer In Drying Process Of Moist Porous Media

Wet porous media drying is a complex process involving simultaneous heat and mass transfer. Although many scholars performed relevant experimental and theoretical researches, more systematic study on heat and mass transfer mechanisms is still lacked. Therefore, developing and solving a rigorous mathematical model of heat and mass transfer in porous mediadrying for accurate prediction and analysis of drying process remain worthy and intersrting.A numerical investigation was carried out on fluidized-bed drying of porous media through numerically solving the mathematical model of coupled heat and mass transfer developed in this Master's research. Based on the mechanisms of fluid flow. Mechanisms of multi-phase heat and mass transfer inside porous materials were first analyzed systematically based on the porous media theory, and heat and mass flux equations of liquid, gas and solid phases were given, respectively. The general governing equations of moist porous media drying were derived based on the classical transport theory combined with Whitaker's volume-averaging theory. The equation set was closured by using heat and mass transfer between porous media and surroundings under circumstance of fluidized-bed drying as external boundary conditions. The governing equations were then simplified into one-dimensional form of spherical coordinate system and two-dimensional form of cylindrical one for specific purposes. The finite-volume method with the fully implicit scheme was adopted for discretization of governing equations. Physical properties of apple were used in the present simulation.The effects of temperature and saturation inside particles on the effective conductivities were examined based on heat and mass flux equations. Under typical operating conditions, heat and mass transfer mechanisms were analyzed and the drying rate-controlling factor was discussed according to the profiles of temperature, saturation and pressure. Under different operating conditions, the effects of gas inlet temperature, gas inlet velocity and bed area factor were investigated. Results show that the drying process can be significantly affected by coupled heat and mass transfer between gas and solid phases. The drying time decreases with increase in the gas inlet temperature and velocity. while increases with increase in the bed area factor.