Phase-field LBM simulation of evaporation and condensation in regular porous media: A unit-cell study

In this study, phase change phenomena in porous media are investigated using the phase-field lattice Boltzmann method combined with the Hertz–Knudsen–Schrage phase change relation. To systematically analyze the effects of porous structure and wettability, two types of regular porous media—aligned and staggered configurations—are considered, each with high and low porosity levels. A range of contact angles (30°, 45°, 60°, and 75°) is examined to capture the influence of wettability on evaporation and condensation processes. The simulation conditions are designed to resemble heat pipe operating regimes, with a small temperature difference (ΔT=5 K) and pore sizes between 35 and 50 µm. The results reveal that during evaporation, liquid pinning at the solid interfaces plays a critical role in enhancing the phase change rates, while in condensation, the behavior is less sensitive to pinning. It is shown that increasing the contact angle generally reduces the evaporation rate, while its effect on condensation is less straightforward. Additionally, analysis of contours highlights the edge-dominant nature of the phase change within the porous structures. The evaporation rate is similar in the aligned and staggered structures, but dropping the porosity from ε=0.75 to 0.57 cuts the rate by about 20%–25% at θ = 30°. For condensation, the staggered structure yields 60%–70% higher rates than the aligned one, yet the same porosity drop still cuts the rate by roughly 55% at the same contact angle. The outcomes provide fundamental insights for designing porous media in applications such as heat pipes, where efficient phase change is essential.