Selection of convective moisture transfer driving potential and its impacts upon porous plate air-drying characteristics

Abstract A theoretical model is developed to simulate the convective air-drying process of an unsaturated porous plate using the representative elementary volume (REV) approach. The model considers a variety of transport mechanisms and uses the specific humidity (mass fraction) as the convective mass transfer driving potential, which is thought to suit for modeling of non-isothermal water evaporation into air fluid. The partial differential equations included in the model are discretized and solved fully implicitly using the predicator-corrector method. Calculations are performed with two water vapor concentrations including the specific humidity and vapor density as the mass transfer driving potential to clarify how the potential selection will affect the drying characteristics. Calculations are performed for plate thickness of 15 mm and air temperatures of 320.15, 333.15 and 348.15 K. The results show that use of the vapor density as the driving potential causes underestimations of the wet surface temperature and plate moisture content, and this tendency becomes more conspicuous for a lower air temperature. It is recommended to use the specific humidity as the mass transfer driving potential to better describe the moisture and heat transfer during the convective drying of an unsaturated porous medium.