CONTROL OF POOL BOILING HYDRODYNAMICS THROUGH SURFACE WETTABILITY PATTERNING
Boiling surface enhancements including engineered wettability, porous coatings, and other geometric modifications have long been explored to meet increasing heat dissipation requirements. Recent investigation of the effects of biphilic surfaces, i.e., those with intermixed wetting and non-wetting regions, on pool boiling heat transfer have indicated potential enhancements of both the boiling heat transfer coefficient and the critical heat flux (CHF) compared to a uniform hydrophilic surface. There is no unified explanation for the CHF enhancement mechanism on biphilic surfaces, which does not follow the accepted understanding of the effects of uniform surface wettability on CHF and boiling hydrodynamics. In this study, we fabricate biphilic surfaces with the goal of controlling liquid-vapor hydrodynamics, as a potential enhancement mechanism. The surfaces feature alternating superhydrophobic and hydrophilic stripes of equal width. The stripe widths differ from surface to surface while the total area of each wettability type is maintained at 50% each, to identify the impact of this stripe width on the boiling behavior. Unlike prior studies, the superhydrophobic surface texture is infiltrated with liquid prior to boiling, i.e., brought into an initial Wenzel state. Nucleate boiling from this initial state prevents vapor bubbles from spreading over these regions and enables large superhydrophobic areas to be incorporated without detrimental effects on CHF. Nucleation preferentially occurs on the superhydrophobic regions, allowing control of the hydrodynamics via the surface wettability patterning. The heat transfer coefficient and CHF improve as the stripe width decreases under this mode of boiling; the possible mechanisms of enhancement on biphilic surfaces are discussed based on evaluation of prevailing theories.