Liquid film flow boiling heat transfer on cylinder for successive droplets impact

Abstract

The situation on boiling heat transfer when droplets impact on heated cylinder is popular in the industrial applications, but the research in this field is very lacking. In this paper, an experiment that generates continuous high heat flux in one-dimensional heat conduction was designed to study the liquid film flow boiling heat transfer on cylinder for successive droplets impact, and the effects of droplet impact frequency and droplet impact velocity were analyzed. The results show that, at the single-phase heat transfer stage, increasing the droplet impact frequency or impact velocity can promote heat transfer performance. At the initial stage of nucleate boiling, increasing the two influencing factors makes more heat be taken away by sensible heat and latent heat of liquid vaporization. However, at the later stage of nucleate boiling, the droplet impact frequency has little effect on the heat transfer performance. The heat converted into the sensible heat of liquid is small due to low impact frequency, but the elevation of latent heat of liquid vaporization makes up for the shortage, resulting in the heat transfer performance being unexpectedly similar with the high impact frequency. At this stage, increasing droplet impact velocity does not affect the heat taken away by the sensible heat of liquid, but boosts the liquid vaporization rate and utilizes the latent heat of vaporization. Furthermore, the triggering mechanism of critical heat flux on the cylinder was revealed, which obviously differs from the case of droplets impacting on the flat surface. Finally, an empirical correlation to predict the boiling heat transfer characteristics was established.