Experimental Study And Numerical Simulation On Mechanism Of Heat And Mass Transfer In Wet Porous Media

The heat and mass transfer process in wet porous media is a common phenomenon in nature and human life.Therefore,it has great application significance and scientific value to study the heat and mass transfer process in porous media.The heat and mass transfer in micro scale determines the macroscopic transport phenomena,hence,to explore microscopic heat and mass transfer mechanism is helpful to understand the macroscopic properties of heat and mass transfer in porous media.In this paper,stacked sands were used as porous medium,and the water morphology in wet sands samples was observed by a CCD combined with a stereo microscope.Meanwhile,to analyze the mechanisms of heat and mass transfer of porous media in pores,the experimental observation of water diffusion was conducted with heating.The results show that liquid mainly exists as liquid bridges in porous media with relatively low liquid content.With heating,the water near the heat source evaporates and diffuses to the relatively far region,and results in the decrease of the moisture content in the heating source adjacent region.However,in samples with low liquid content,liquid bridges in different pores do not contact with each other,so the liquid cannot “jump” between different pores and thus there is almost no liquid flow in the porous media.For porous media with relatively high liquid content,the liquid in different pores usually connects to each other,therefore liquid can flow in pores by the capillary force.A model is proposed to describe the heat and mass transfer in saturated wet porous media based on the experimental results.In this model,a capillary coefficient is introduced to consider capillary driven liquid flow in pores.The temperature distribution and liquid distribution in wet porous media were studied byexperiments and simulation.It showed that,for cases with low liquid content,the simulation results were in good agreement with the experimental results when the liquid flow driven by capillary force ignored.In contrast,for high liquid content samples,the simulation results were close to the experimental results when the liquid flow driven by capillary force was considered.In summary,the capillary driven liquid flow should be ignored in low liquid content porous media which liquid mainly maintains as liquid bridges,and,it should be taken into account in high liquid content porous media which most liquid connects in different pores.