Mesoscale Simulations on the Ultrahigh Heat Flux Evaporation of R143a within Ultrathin Nanoporous Membrane Using a Modified Dimensionless Lattice Boltzmann Method

Abstract

A modified dimensionless pseudo-potential lattice Boltzmann method capable of restoring all related thermophysical properties of any working fluid and spatial/temporal scales of the computational domain is developed in this work. Direct numerical investigations of ultrathin liquid film evaporation of R143a within nanoporous membranes to its ambient pure vapor are carried out. The characteristics of evaporation-driven replenishing flow and the self-regulation of liquid-vapor interface profile under different heat fluxes are captured. In the case of intensive ultrathin liquid film evaporation within nanopore, the apparent contact angle could not reach as small as Young's contact angle θ0 for isothermal conditions due to the self-regulation of liquid-vapor interface. As a result, the maximum capability of nanoporous membranes to replenish the liquid is limited. Under the ambient temperature T0 = 318.19 K, before the three-phase contact line (TCL) recedes into the nanoporous membrane, a heat flux as high as qin,max = 1.52 kW/cm2 can be sustained with a superheat about Ts = 7.79 K for a membrane with pore radius rp = 38.71 nm, pore depth Lp = 294.96 nm, Young's contact angle θ0 = 23° and porosity η = 0.66. The maximum heat flux qin,max increases with the increase of rp and the decrease of Lp and θ0. The present work presents a promising numerical method to optimize thermal management devices using complex micro-nano composite structures.