Numerical analysis of evaporation from nanopores using the direct simulation Monte Carlo method

Abstract

Liquid evaporation from nanopores has been more recent with progress in nanotechnology. The relevant application ranges from solar-driven water harvesting using nanoporous membranes to thermal management of high-power electronics via coolant evaporation from nanoscale pores. In this work, the direct simulation Monte Carlo (DSMC) method was used to simulate evaporation from nanopores into the half-space, with an axisymmetric computational domain which conforms to the real nanopore geometry. According to the position of liquid–vapor interface, the evaporation regime was divided into: pinning and receding. In the pinning regime, the interface was pinned at the top of the nanopores. A range of Knudsen numbers and Mach numbers were compared, and the structure of the Knudsen layer was also identified in detail. The Knudsen layer thickness was less than 10λ at low Mach number and grew to nearly 40λ at Ma∞ = 0.785. We also examined the effects of porosity on evaporation mass flux. The effects of the receding length were researched in the receding regime. The downstream density decreased from 2.4 × 10−3 to 4.29 × 10−4 kg/m3 with the receding ratio from 1 to 20. Furthermore, the evaporation coefficient was established to determine its impact on gas flow. The present results highlighted the non-equilibrium and non-continuum features of nanoporous evaporation, providing insights into the rarefied gas dynamics within nanopores coupled to the liquid–vapor phase change.