Pore-scale effects of geometry and spacing on bubble dynamics and heat transfer in nucleate pool boiling on porous structures

Enhancing pool boiling heat transfer within porous media remains a formidable challenge, primarily due to the intricate coupling between complex structural parameters and multiphase transport phenomena. To bridge the gap between pore-scale hydrodynamics and macroscopic performance, this study employs an advanced cascaded lattice Boltzmann method to rigorously investigate pool boiling on heater surfaces with discrete geometric topologies. Departing from conventional studies focused on homogenized uniform or gradient foams, we elucidate the distinct regulatory mechanisms governing boiling crises at the element level, specifically driven by shape-induced nucleation, vorticity evolution, and capillary-modulated rewetting. Our results demonstrate that triangular topologies induce the highest Nusselt number, where sharp corner singularities accelerate nucleation and promote vigorous bubble departure. Conversely, circular geometries, owing to their symmetry, foster uniform nucleation and stable bubble ascent, offering dynamic stability at the cost of peak heat transfer rates. Trapezoidal structures, however, exhibit disordered phase distribution due to asymmetry, precipitating premature film boiling and suboptimal performance. Furthermore, a critical dimensionless spacing regime (0.65–0.86 capillary lengths) is identified. This regime represents an optimal equilibrium that maximizes beneficial inter-bubble coalescence while sustaining liquid rewetting pathways; deviations lead to either vapor blanketing (narrow spacing) or insufficient flow agitation (wide spacing). Ultimately, this work reveals that performance divergence is fundamentally governed by the synergistic modulation of heat flux concentration, flow confinement, and phase-change thermodynamics, providing vital theoretical guidelines for the topological design of next-generation boiling surfaces.