Direct simulations on the ultrahigh heat flux evaporation of R143a within nanopillars using lattice Boltzmann method with multi-block grid

Direct numerical investigations are conducted to study the ultrathin liquid film evaporation of R143a within square nanopillars using an improved thermal pseudo-potential lattice Boltzmann method (LBM) with a multi-block grid. The simulations successfully capture the evaporation-capillary-driven replenishment flow, the self-regulation of the liquid–vapor interface, and the dynamic evolution of the contact angle under high heat fluxes. At an ambient temperature of 311.27 K, the local critical heat flux (CHF) of the nanopillar surface can reach 2.1 kW/cm2. The results reveal that the CHF is primarily restricted by either the capillary replenishment capability or the thermodynamic limit of homogeneous nucleation, depending on the geometric configurations. With a fixed surface wettability, increasing the nanopillar height or the spatial pitch effectively reduces viscous flow resistance, thereby enhancing the capillary-limited CHF. However, this enhancement eventually reaches a plateau due to the thermodynamic constraint of homogeneous nucleation. This study demonstrates the capability of the LBM in accurately determining the superheat limit of homogeneous nucleation and nucleation site density, providing a theoretical framework for quantifying complex phase-change dynamics in nanostructured surfaces.