Characteristics Of Evaporation From Thin Porous Media

The drying-induced transport phenomenon in porous media is very common not only in nature but also in industrial application,which has an increasingly wide utilization in energy,chemical industry,environmental engineering,agriculture,including specific examples such as proton membrane fuel cell,geothermal energy exploitation,sewage disposal,petroleum exploitation,carbon dioxide sequestration,etc.Evaporation of porous media is a complicated process which involves gas-liquid phase transition,heat and mass transfer and fluids displacement.A fundamental understanding of evaporation characteristics in porous media is of great interest for both industrial application and scientific research.Thin porous media is a typical porous media which is featured by its thickness much smaller than its in-plane dimension,the surface tension is quite important.Free fluids or other external factors have important effect on such porous media.So this study will emphasize on the evaporation characteristics of thin porous media.Evaporation of porous media is a typical multi-scale problem.From the micro perspective,the process is affected by the microstructure,size,topology and connection type of the pore.On the other hand,this process can be described macroscopically.In present study,we first conducted an experiment of water evaporation from glass-silicon chip,obtained gas-liquid interface movement and the gas-liquid phase distribution during evaporation by employing image processing.This experiment further validates the pore-network model with capillary valve effect applied in present study and offers an inspiration for developing new pore-network models in the future.Then a pore-network model is developed to discover evaporation characteristics in thin porous media with mixed wettability from pore-scale and disclose the effect of wettability on the characteristics.A criteria is gained to determine the transition from constant rate period to falling rate period for porous media with mixed wettability.Finally based on the investigation from pore scale,an initial research has been made to evaluate the continuum model by noncontinuum model,the effects of gas invasion pattern on the relationship between diffusivity and local saturation has been studied and we also demonstrated that the diffusivity is not only the function of local saturation,but also the interface area of gas-liquid phase.