Dynamics and heat transfer of a hollow droplet impact on a wetted solid surface

A numerical model based on the coupled level set and volume of fraction (CLSVOF) method is developed to investigate dynamics of a hollow droplet impacting on a wetted solid surface and the associated heat transfer process. Numerical results show different impact behaviors of the hollow droplet as compared to a continuous dense droplet. One of the distinctive flow features of the hollow droplet is a central counter jet, which is not present in continuous dense droplets. Analysis of pressure distribution indicates that the central counter jet is mainly due to the pressure gradient inside the hollow droplet during the impact and spreading. Simulation results also show that the impact velocity of the hollow droplet determines its spread factor, dimensionless spreading edge-jet height and central counter-jet height, all with positive relations. The complicated transient heat transfer between the impacting droplet and the surface was analyzed. The average heat flux increases with higher impact velocity. Overall heat transfer during hollow droplet impact is found to be lower than that during continuous dense droplet impact. These results provide better understanding of hollow droplet impingement and heat transfer on wetted surfaces. (C) 2018 Elsevier Ltd. All rights reserved.