Abstract
Multi-droplet impact on a thin liquid film covering a heated wall is numerically studied using a three-dimensional model with an implement of a random disturbance subjected to Gaussian distribution. The model can effectively simulate the splashing process after droplets impingement. Results show that simultaneous impact lowers splashing threshold due to cracking of central liquid sheet, while successive impact results in higher splashing threshold for the trailing droplet than the leading one due to radial flow inside the residual film. Single-phase heat transfer coefficient in the impinged region is remarkably higher than the undisturbed film region, caused by flow enhanced convective heat transfer. A heat transfer blind spot situated under the central liquid sheet in simultaneous impact is identified, at which relatively high local temperature is observed and heat is more difficult to be rejected due to flow stagnation there. Cooling of the heated wall in successive impact is mainly achieved by contacting of the trailing droplet with the heated wall, rather than mixing of cold droplets and warm film. This study discusses the effects of Weber number, wall heat flux and droplets horizontal/vertical interval on the heat transfer coefficient.
