Experimental studies of droplet nucleate boiling characteristics on micro-cavities surfaces with different wettability

Abstract

In this study, micro-cavities surfaces with different wettability are prepared by combining nanosecond laser micro-nano processing technology, chemical oxidation and electrochemical corrosion. The effects of micro-cavities and surface wettability on evaporation time and bubble dynamics are experimentally investigated. The results show that micro-cavities surfaces with smooth structures exhibit excellent evaporation performance as micro-cavity serves as the nucleation site for bubble. The existence of CuO film on micro-cavities surfaces with superhydrophilic structures increases the thermal resistance and hinders the bubble growth, which causes poor droplet evaporation process. On the other hand, the Rayleigh-Taylor instability is easily triggered on micro-cavities surfaces with superhydrophobic structures due to lower surface tension of the solid–liquid interface. This phenomenon causes the strong fluctuation and prolongs the evaporation process. The vapor jet or fluctuating liquid–air interface is observed at the droplet center from the thermal pattern of micro-cavities surfaces with smooth structures. On micro-cavities surfaces with superhydrophilic structures, the fluid at the top of droplet has an obvious temperature gradient due to the existence of vapor bubble. However, strong fluctuation is developed on micro-cavities surfaces with superhydrophobic structures, leading to the fact that the fluid near the liquid–air interface is cooled. Entrapped air inside the micro-cavities serves as the bubble seed for micro-cavities surfaces with smooth structures and micro-cavities surfaces with superhydrophobic structures, thus shortening the time for bubble nucleation.