Hybrid lattice Boltzmann study of boiling in 2D porous media with comparison to pool boiling

Boiling heat transfer, renowned for its exceptional efficiency, has become the preferred choice in numerous engineering applications due to its ability in achieving high heat flux under low wall superheat. The heat transfer is influenced by multiple parameters, including surface wettability, contact angle, and solid geometry, etc. While extensive researches focused on boiling over flat walls, the understanding of these parameters on boiling within porous media remains very limited. Using a hybrid thermal two-phase lattice Boltzmann model (LBM), this study explores the boiling heat transfer in 2D porous media. First, the hybrid model is validated by single-droplet evaporation and single-bubble boiling. Subsequently, the boiling heat transfer in porous media under different wall superheat and contact angles was systematically investigated and compared with boiling on flat wall. The corresponding boiling phenomena and the heat transfer curves are analyzed. The results reveal that, compared to flat walls, porous media significantly enhance both maximum boiling heat flux and effective boiling range (from onset of nucleate boiling to film boiling). At neutral surface wettability, porous media leads to flux enhancement (up to 31.9% at 90°) while with hydrophobicity, porous media maximizes the effective boiling range (6-fold at 120°). On the other hand, hydrophilic walls universally improve heat flux and boiling range for both structures, and exhibit stronger effects on flat walls (e.g., 62.5% of effective boiling range increase). Conversely, hydrophobic walls depress onset temperatures across all regimes and suppress heat flux similarly in both configurations, though the constraining effect on the boiling range of porous media is markedly weaker.