Department of Mechanical Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
Phys Rev E. 2017 Oct;96(4-1):043112. doi: 10.1103/PhysRevE.96.043112. Epub 2017 Oct 30.
We investigate the effect of capillary condensation on gas diffusivity in porous media composed of randomly packed spheres with moderate wettability. To simulate capillary phenomena at the pore scale while retaining complex pore networks of the porous media, we employ density functional theory (DFT) for coarse-grained lattice gas models. The lattice DFT simulations reveal that capillary condensations preferentially occur at confined pores surrounded by solid walls, leading to the occlusion of narrow pores. Consequently, the characteristic lengths of the partially wet structures are larger than those of the corresponding dry structures with the same porosities. Subsequent gas diffusion simulations exploiting the mean-square displacement method indicate that while the effective diffusion coefficients significantly decrease in the presence of partially condensed liquids, they are larger than those in the dry structures with the same porosities. Moreover, we find that the ratio of the porosity to the tortuosity factor, which is a crucial parameter that determines an effective diffusion coefficient, can be reasonably related to the porosity even for the partially wet porous media.
我们研究了在具有中等润湿性的随机堆积球体组成的多孔介质中，毛细凝结对气体扩散系数的影响。为了在保留多孔介质复杂孔隙网络的同时模拟孔尺度上的毛细现象，我们采用了粗粒化格子气模型的密度泛函理论（DFT）。格子 DFT 模拟表明，毛细凝结优先发生在被固体壁包围的受限孔隙中，导致狭窄孔隙的阻塞。因此，部分润湿结构的特征长度大于具有相同孔隙率的相应干燥结构的特征长度。随后利用均方位移方法进行的气体扩散模拟表明，尽管在部分凝结液体存在的情况下有效扩散系数显著降低，但它们大于具有相同孔隙率的干燥结构的有效扩散系数。此外，我们发现，决定有效扩散系数的关键参数孔隙率与迂曲度因子的比值，即使对于部分润湿的多孔介质，也可以与孔隙率合理相关。
