Limited Enhancement of Subatmospheric Boiling on Treated Structured Surfaces With Biphilic Pattern

Abstract Boiling heat transfer suffers deteriorations under subatmospheric conditions, which can be attributed to a shortage of viable nucleation sites at declining pressures. In this work, the possibility enhancing low-pressure saturated boiling water using combination wettability patterning and structural modifications was experimentally explored. The copper test surface, comprised an array circular “dimples” (0.3 mm in depth, 0.5 diameter, 3.0 pitch), spray-coated by polytetrafluoroethylene (PTFE) coatings so as form matching biphilic pattern with surface cavities. resulting dimpled showed appreciable enhancement—with maximum 60% increase average coefficient nucleate compared flat surface—down about 9.5 kPa. Further lowering pressure 7.8 kPa, however, found lead diminished performance gains. visualization study bubble departure dynamics revealed signs additional vapor trapping hydrophobic-coated cavities, induce uninterrupted regeneration zero waiting time explain qualified enhancement boiling. Thanks potential secondary pinning contact line inside hydrophobic incomplete detachment could prevail somewhat lower pressures than otherwise possible without dimple structure, leaving behind significantly more residues. However, vapor-trapping capacity decrease pressure, provided clues regard reduced efficacy even