Experimental study of two-phase heat transfer of droplet impact on liquid film

Abstract

Spray cooling is an effective heat transfer technique capable of handling high heat fluxes and temperatures. The study of droplet impact offers a simplified approach to understanding the fundamentals of spray cooling and elucidates the effects of droplet diameter and velocity. Experiments on a single-droplet impact on a thin liquid film with boiling bubbles are carried out in this study. Two-phase interface evolution is observed using high-speed video, and the heater surface temperature variation at the impact point following an impact is recorded and analyzed, which can be divided into the response stage, the recovery stage, the steady stage, and the slow recovery stage. Furthermore, a cooling factor based on the change in heater surface temperature is introduced to evaluate the cooling effect of droplet impact. Results show that the steady stage plays a significant role in the heater surface cooling process. Moreover, the maximum cooling factor increases appreciably with increasing droplet diameter and impact velocity.