Influence of the governing dimensionless parameters on heat transfer during single drop impingement onto a hot wall

The cooling effectiveness of spray cooling is strongly influenced by droplet size and velocity as well as by the fluid properties. To enhance the understanding of the entire process, first of all basic processes occurring in the spray have to be addressed. Therefore, in this study the heat transfer during a single drop impingement onto a dry, superheated wall is investigated numerically, and the effects of the dominating dimensionless parameters on the convective and evaporative heat transfer are analyzed. In order to be able to distinguish between the influences of the individual dimensionless groups, each parameter is varied individually. The study is performed using fluid properties of the refrigerant FC-72. The droplet is surrounded by a saturated vapor atmosphere. The numerical model accounts for the complex two-phase flow, the transient conductive heat transfer within the solid domain and the evaporative mass transfer. Special attention is paid to the local heat and mass transfer close to the moving three-phase contact line. The spreading phase appears to be dominated by the Reynolds number, while in the receding phase the Weber number has the strongest influence on heat transfer. For the evaporation of a sessile droplet, which is the final stage of the impact process, the heat transfer is governed by the Bond number.