Three-dimensional pore-scale simulations of thin-film evaporation on micro-pillar wicks

This study presents three-dimensional pore-scale numerical investigations of thin liquid film evaporation on hydrophilic micro-pillar array wicks, utilizing the pseudo-potential multiple-relaxation-time lattice Boltzmann liquid–vapor phase-change method. The simulation captures both the steady-state meniscus morphology and the dynamic recession behavior during dryout, offering pore-scale insights into the evaporation-to-dryout transition. At the pore scale, we numerically capture the profile of the curved meniscus during steady-state evaporation, as well as its continuous recession during dryout after surpassing the capillary-driven dryout heat flux. A parametric study is conducted to systematically investigate the effects of wettability, pillar pitch, and pillar height on the dryout heat flux. A thermal-fluidic analytical model for predicting capillary-driven dryout heat flux is applied to verify the simulated dryout heat flux and wickabilities of the micro-structured wicks. We demonstrate that wickability—characterized by both the liquid front velocity and the volumetric wicking flow rate—governs the capillary-limited heat transfer performance. We find that the influence of both wettability and pillar pitch on the dryout heat flux is primarily attributed to wickability, as characterized by the liquid front propagation rate. While the liquid front propagation rate initially increases and finally flattens out with increasing pillar height, the wickability characterized by volumetric wicking flow rate continues to rise with the increasing pillar height. The analytical predictions for the capillary-limited dryout heat flux demonstrate good agreement with the simulation results. This work advances the understanding of pore-scale evaporation and offers design guidelines for optimizing capillary wick structures in thermal management applications.