Droplet impact on superheated surfaces with different wettabilities

Abstract

In this work, single droplet impact on superheated surface with 5 to 220 Weber numbers, 110 °C to 360 °C surface temperatures and 10°, 78° and 122° surface contact angles of deionized water was experimentally investigated. The surface wettability was changed by spray-coating thin films on the aluminum plates and the surface roughness maintained very small. Six typical droplet impact and boiling modes were observed and classified. The Ts-We regime map was used to illustrate the droplet impact and boiling modes. The results show that the surface temperature required for the transition from droplet boiling with atomization to droplet boiling without atomization increases with the increase of Weber number and surface wettability. The curve separating the droplet rebound with atomization mode and droplet breakup with atomization mode is not monotone on the hydrophilic surface and bare aluminum surface. On the hydrophilic surface, the recoil of the spread film is very weak at the deposition mode and droplet rebound requires higher surface temperature. Besides, the droplet breakup will not occur on the hydrophilic surface with lower surface temperature (Ts ≤ 150 °C). On the hydrophobic surface, the deposition mode is absent and atomization cannot be observed for any surface temperatures when the Weber number is small (We = 5 or 20).