An Experimental Study of a Single Droplet Impacting Onto a Heated Surface at High Impact Weber Numbers

Spray cooling is known to be one of the most effective methods of cooling high heat flux electronics. In order to better understand the fundamental physics and heat absorption of spray cooling, single droplet impingement on a heated surface has gained numerous attention. Although extensive research has been performed on single droplet impingement, the literature is sparse regarding the study of the heat transfer at high impact velocities. Upon the impact of the droplet, the surface temperature drops dramatically and rapidly. At higher impact conditions this temperature drop is even more severe and therefore fast response thermal instrumentation is required to measure the instantaneous surface temperature. In this work, intrinsic thermocouples were designed and fabricated to effectively capture the dramatic surface temperature gradient immediately upon the impact. High speed digital video camera was utilized to capture the hydrodynamics of the droplet, the spreading and receding phases, and to observe the evaporation process. It was found that the surface temperature dropped more significantly as impact We number was increased. This was due to the formation of a larger diameter and thinner liquid film on the heated surface. Consequently, the evaporation rate was found to increase as impact We number was enhanced.