Mesoscale simulation of the equilibrium state of the confined nanoscale two-phase flow in the presence of corner interface and adsorbed liquid layer

Abstract

The equilibrium phase behavior of fluids in confined nanopores shifts from that at the bulk conditions because of the interaction between fluid and solid molecules, known as the adhesive force. In the present study, a two-Phase Lattice Boltzmann approach is utilized to directly model methane’s phase equilibrium in nanochannels. The impacts of the domain temperature, the nanochannel cross-sectional geometry, and the solid–fluid adhesive strength on the equilibrium between the vapor and liquid phase in a confined space and the thickness of the liquid adsorbed layer are investigated. First, the outcomes from the Lattice Boltzmann method for flat and curved interfaces are validated against the reconstruction of the macroscopic Maxwell Equation and Kelvin’s equation using the Carnahan-Starling equation of state, respectively. Second, the equilibrium state of a liquid plug in channels of triangular, square, octagonal, and circular cross-sections with different solid–fluid interaction strengths are investigated. It is observed that by decreasing the angle of the cross-sectional area’s corner, reducing the adhesive force’s strength, and raising the domain temperature, the equilibrium state becomes closer to the bulk saturation state. Besides, it is found that the deviation between the simulation and Kelvin’s prediction is higher for a channel with a smaller hydraulic diameter and less domain temperature. Furthermore, when the condensed liquid layer is in equilibrium with a corner interface, the pressure of the gaseous side remarkably declines with the rising of the solid–fluid adhesive strength. In addition, for nanoconfined two-phase flow, the heterogeneity of the density distribution at a specific temperature is affected by the shape of the nanochannel cross-sectional area and the strength of the adhesive interaction.