Biphilic surface to improve and stabilize pool boiling in vacuum

Abstract

• Water pool boiling performance on a biphilic surface at 10–103 kPa was studied. • The change in bubbles dynamics compared to bare surface was observed. • The heat transfer enhancement up to 3.7 times was obtained. • Biphilic surface led to boiling stabilization at pressures down to 10 kPa. To date the usage of biphilic surfaces is one of the most promising ways to simultaneously enhance heat transfer and increase critical heat fluxes during boiling. However, the vast majority of studies devoted today to the influence of surfaces with mixed wettability on boiling performance refer to atmospheric pressure conditions. At the same time, the problems of heat transfer rate increasing and stabilizing the boiling process at subatmospheric pressures are particularly acute, which is associated with some features of boiling in a vacuum and its high practical relevance. The paper presents the results of experimental study on the local boiling characteristics, including the bubble departure diameters and emission frequencies, and the heat transfer rate during water boiling on a biphilic surface in the pressure range of 10–102 kPa. As a result of experiments, it was shown that the hydrophobic areas of the fabricated biphilic surface are the sites of continuous vapor bubbles generation in the entire range of the studied pressures. At the same time, the slight increase in the size of detached bubbles and their emission frequency from the hydrophobic spots was observed with pressure reduction. It was also demonstrated that in the range of low pressures (less than 40 kPa), the biphilic surface is characterized by noticeably smaller bubble departure diameters and much higher emission frequencies compared to bare surface. The analysis of boiling curves obtained using IR thermography revealed that the developed biphilic surface provides a significant heat transfer enhancement - up to 3.7 times during boiling at subatmospheric pressures compared to bare surface. Moreover, a significant decrease in the surface superheating and in the amplitude of integral temperature oscillations is observed, which represents the boiling stabilization at low subatmospheric pressures (less than 20 kPa) for the fabricated surface.