Capillary condensation in porous media considering a phase transition multiphase model

Resumo

Capillary condensation in building porous materials and the correct understanding of its underlying physics, leading to the enhancement of vapor transfer at low moisture contents, is a challenging research theme. In porous constrictions, the adsorbed moisture onto the solid surfaces of a porous material can grow around these surfaces, leading to what we know as capillary condensation: these constrictions are filled with liquid and, in consequence, form bridges, enhancing vapor diffusion through the porous material. Capillary condensation, thus, results from the intermolecular attraction forces between the vapor and the liquid molecules that are adsorbed onto the solid surfaces around constrictions. Vapor sorption has been modeled for materials presenting high hygroscopicity by considering the thermodynamic stability conditions of two-phase systems in single cavities of simple geometry, such as cylinders or spheres (Philippi et al., 1994), (Dutra et al., 2017). The continuous development of more rigorous molecular-based models of fluid systems, together with advances in computational resources, has resulted in an improved understanding of the underlying physics of these systems. In this study, an isothermal multiphase lattice-Boltzmann model with phase transition (Siebert et al., 2014) is used to simulate vapor condensation on the surface of a pore constriction represented by the spacing between two spheres (or cylinders in a two-dimensional simulation). The spacing between the solid bodies dictates if the liquid layers adhered to the walls give rise to capillary condensation. The results tend to agree with the Young-Laplace law.  References Dutra, L., Mendes, N., & Philippi, P. (2017). On the characterization of pore size distribution of building materials. Journal of Building Physics. https://doi.org/10.1177/1744259117698515 Philippi, P. C., Yunes, P. R., Fernandes, C. P., & Magnani, F. S. (1994). The microstructure of porous building materials: study of a cement and lime mortar. Transport in Porous Media, 14(3), 219–245. https://doi.org/10.1007/BF00631003Siebert, D. N., Philippi, P. C., & Mattila, K. K. (2014). Consistent lattice Boltzmann equations for phase transitions. Physical Review E, 90(5), 053310. https://doi.org/10.1103/PhysRevE.90.053310