Nucleation, growth and bubble detachment in liquid-vapor phase change on structured surfaces

Abstract

Comprehensive grasp of heat and mass transfer, particularly in applications involving liquid-vapor phase change, hinges on management of nucleation, growth, and detachment of vapor bubbles. Various parameters influence the dynamics of phase-change heat and mass transfer and thus dictate the interactions between the surface, the liquid, and the vapor, profoundly impacting the underlying processes. To tailor these phenomena and harness them for technical applications involving high heat flux densities and intense mass transfer, such as boiling and electrolysis, surface functionalization is under intense development. By designing structured surfaces and creating preferential nucleation sites that promote heterogeneous nucleation, it is possible to exert control over the location and density of active nucleation sites on the surface. This, in turn, enables the regulation of bubble growth and detachment from the surface. With the aim of identifying optimal surface treatments for functionalizing surfaces and enhancing their performance in phase-change applications, we evaluated the nucleation, growth and detachment of a single bubble in a liquid-vapor phase change on untextured and laser-textured surfaces during water electrolysis. Platinum was chosen as the preferential material due to its favourable electrochemical properties for the hydrogen evolution reaction in acidic media. Electrolysis was performed at various voltages and the bubble dynamics were evaluated through high-speed imaging to investigate the intricacies of bubble growth and their mutual interactions. At 3.5 V using the laser textured surface, hydrogen bubbles detaching from the electrode surface had on average 40% smaller diameter, while the frequency of their detachment was 2,5-times higher compared to the untextured surface. This opens the possibility for further research that could lead to improving the efficiency of electrolysis.