Effects Of Liquid Morphology On Properties Of Porous Media Made Of Stacked Particles

The heat and mass transfer process of porous media exists widely in the nature and our life, so the research on porous media has great engineering background and scientific value. Most research efforts on porous media are based on homogenization approach, and thereby ignore the detailed micro-scale effects. So considering the micro-scale effects, the study on the influence mechanism of liquid content on apparent characteristics and macroscopic transport properties of porous media will contribute to making a deep understanding of the influence factors of macroscopic properties.The theoretical research on heat transfer of wet porous media focuses more on the relationship between the thermal conductivity and water content, particle diameter, temperature, et al. And the experimental research mainly focuses on the trend of thermal conductivity with the change of water content and rarely pays attention on the micro-scale effects. With the change of liquid content, the liquid morphology present different state, this will affects the particles aggregation state and the apparent characteristics and macroscopic transport properties of porous media.Glass beads are used as particles stacked porous medium, and the liquid content is Water, O.Olmol/L NaCl solution and 0.02mol/L KC1 solution. The microstructure in the wet porous media is observed by a CCD combined with a stereo microscope. The samples apparent volumes at different moisture content were measured. Thermal conductivity was obtained by a thermal constant analyzer (TPS 2500S). Two-electrode method was used to determine the electrical conductivity.By the micro view observation experiment, it shows that the liquid mainly existed as liquid bridge at low liquid content, while liquid in different pores connected to each other at higher liquid content. The liquid effect on particles altered with a variation of the transformation of liquid morphology and distribution, resulting in changing the aggregation state of particles and the apparent properties of the porous media. Besides, the incremental rate of electrical conductivity presents a different trend within different liquid content range. The electrical conductivity increases slowly within low liquid content, and it increases rapidly when liquid content in samples exceeds a certain liquid content, this is caused by the change of liquid morphology and distribution. In another word, besides the micro view observation experiment, the critical liquid content at which the liquid morphology shifts from a state with liquid bridge into an interconnected state can be determined by the result of electrical conductivity.A theoretical model based on the experiments is built. This derives the functional relation between the critical liquid content and the contact angle of liquid. Furthermore, the prediction from the model is in good agreement with the experiment.