Numerical simulation of boiling in wick structures: Comparative analysis of mono-, Bi-, and hybrid porous media

Efficient thermal management is critical in high-power electronic and energy systems, where overheating can lead to performance degradation or material failure. Capillary-driven boiling in porous media is a promising passive cooling solution. The advent of advanced fabrication methods, such as additive and subtractive manufacturing, enables controlled fabrication of porous structure geometry. However, limited research exists to numerically guide porous structure design and explore the complex pore-scale two-phase interplay during the boiling phenomena. The present work provides an in-depth pore-scale numerical investigation of capillary-fed boiling in three porous configurations: monoporous, biporous, and hybrid (combining mono- and biporous) media. Simplified cluster geometries were used to model complex biporous and hybrid structures, and simulations were carried out spanning heat flux levels from 1 to 50 W/cm², validated against experimental data. At low heat fluxes, monoporous and hybrid wicks outperform biporous ones due to reduced vapor entrapment. However, at high heat fluxes, biporous structures exhibit superior performance, thanks to their higher permeability and stronger capillary pumping, which enhance vapor removal and liquid replenishment. Under the peak tested heat flux of 50 W/cm², the biporous media achieves the lowest wall superheat (∼15 K) and vapor saturation (∼0.25), indicating the highest resistance to dry-out. The hybrid wick demonstrates the best performance under low to moderate heat fluxes, whereas at high heat flux levels it exhibits intermediate performance, benefiting from both monoporous and biporous characteristics. The results in this work elucidate the complex two-phase boiling phenomena in varied porous structure geometries that have been commonly experimentally applied. As such, it may serve as a design guide for future advanced wick structures in high-performance cooling systems.