International Journal of Heat and Mass Transfer, Vol.131, 999-1008, 2019
Water film coverage model and its application to the convective air-drying simulation of a wet porous medium
A novel model named the water film coverage model is proposed to quantitatively describe the surface moist situation of a wet porous medium during its convective air-drying process, it assumes that the medium surface exposed to hot air undergoes three stages, i.e. the fully wet, partly wet, and fully dry stages, as compared to the two stage assumption made by the traditional model. The model contains two parameters including the critical water saturation at medium surface at which the water film begins to break, and the coverage constant that characterizes the water film coverage. By combining this new model with our previous porous medium air-drying model, which considers a variety of transport mechanisms and uses the specific humidity as the convective moisture transfer driving potential, a comprehensive model for predicting the air-drying process of a wet porous medium is obtained. Air-drying experiments are conducted to validate the model, they are carried out on a wet sand layer, which consists of silica sand and distilled water and has a thickness of 15 mm, for hot air temperatures of 318.15, 333.15 and 348.15 K. The experimental results show that the sand layer temperature continuously increases throughout the drying process, there is no period during which the sand layer temperature remains constant at the air wet-bulb temperature, as predicted by the traditional model. Comparison of the simulations and experiments supports that the present model can better predict the sand layer temperature and moisture content evolutions than the traditional model. The critical water saturation has a value close to the initial water saturation of the wet sand layer, while the coverage constant takes a value less than unity, which corresponds to an upward convex coverage curve. The present model will reduce to the traditional model when the critical saturation is taken to be equal to the irreducible saturation or the coverage constant is set to be zero.(C) 2018 Elsevier Ltd. All rights reserved.