Description of confined nanoflow transport considering the effects of capillary condensation and heat transfer by means of a two-phase lattice Boltzmann model

Abstract

The pseudopotential two-phase Lattice Boltzmann method is used to study a flow with condensation and evaporation through slits ranging between 8 to 24 nm in width by applying a pressure gradient. The slits are about 700 nm long. The fluid described by the Carnahan-Starling equation of state is in the form of a vapor upstream of the pore. For the smaller applied pressure gradient, the vapor flows through the slit. However, for higher values of the pressure gradient, as the gas flows through the slit, the fluid condenses, and consequently, liquid flows through the slit. The liquid may leave the slit, or it evaporates. Here, the condition at the interface between the liquid and the gaseous flow region, where mass transfer by evaporation takes place, is investigated. The pressure difference across the curved meniscus is consistent with the Young-Laplace equation and nearly independent of the mass flow rate. However, the curvature of the interface depends on the strength of the fluid-wall interaction. The curvature of the meniscus and effects influencing the curvature play an important role in the process. Considering the temperature field in the transport process reveals that different boundary conditions for the domain influence the mass flow rate. Heating the slit from the downstream side decreases the mass flow rate.