Study On Mechanism Of Heat And Mass Transfer In Unsaturated Wet Granular Porous Media

The heat and mass transfer of granular and unsaturated wet porous media is common in nature and daily life.To probe into their internal heat and mass transfer behavior and basic mechanism has important academic significance for many disciplines and fields.The liquid distribution in the unsaturated wet porous medium is different with different liquid content,which has a significant influence on its overall transfer characteristics.Therefore,in order to understand the heat and mass transfer process of wet porous media,the influence and the intrinsic the mechanism of the liquid distribution and its diffusion process on the heat and mass transfer phenomenon in the pore scale are studied in this paper.Packed sands are taken as the granular porous media.With different water content,water distribution in the samples and the water evolution process under heating conditions are recorded by high-speed CCD.It is found that with low liquid content,the liquid in pores is mainly exists as the form of liquid bridge,and the water masses between different pores are mostly isolated.In the cases of high liquid content,the water masses between different pores are mostly interconnected.By adding tracer to the samples,it is found that,with low liquid content,the liquid in the near heat source region is reduced apparently due to the evaporation by heating,and the liquid in the relative far region are still maintain a relative high liquid content.The reason is that,though there is a capillary pressure difference between the near heat source region and the far region,the water at the relative region cannot be replenished to the near heat source region for the liquid cannot “jump” due to the liquid masses in different pores are not connected to each other.When the liquid content is high,the water reduce in the near heat source region is not notable because the water between the different pores is mostly connected to each other and the liquid at the far region will move to the near heat source by capillary pressure difference.Based on the experiments,a model of heat and mass transfer in unsaturated wet porous media was established.The internal temperature field evolution of the wet sample under thermal conditions was numerically simulated and compared with the experimental results.Through analysis,it is found that the heat and mass transfer of unsaturated wet porous media should consider the effect of gravity on the gas phase,and the effect of gravity on the liquid phase can be ignored.Under the condition of low liquid content,the liquid phase should not consider the capillary pressure difference effect.However,for high liquid content,the influence of capillary force on the liquid heat and mass transfer must be considered.By comparing the experimental and simulation calculation results,the model describing the heat and mass transfer in unsaturated wet porous media,which considering critical liquid content,was further modified.