Asymmetric heat transfer characteristics of a double droplet impact on a moving liquid film

In this work, a coupled level-set and volume of fluid method is employed to investigate a two-dimensional double droplet impact on a moving liquid film. The flow and heat transfer characteristics are analyzed for various film moving velocities, horizontal spacings between the two droplets, impact velocities, and film thicknesses. The results show that four small jets occur near the neck at the contact regions between the droplet and film at the initial impact stage. Subsequently, the two peripheral jets expand outward and form a crown, while two inner jets merge into a central uprising jet. The largest local wall heat flux appears in the two impact regions; however, three extra peaks are observed in the jet regions due to the enhanced convection heat transfer. As compared with impact on the stationary film, the peripheral and central jets for impact on the moving film exhibit an asymmetric feature due to shearing effect of the film, leading to an asymmetric and enhanced local wall heat flux. The asymmetry becomes more significant for larger film moving velocities. The heat transfer enhancement in the impact region is more remarkable for a smaller spacing between the two droplets, a higher impact velocity, or a thinner film thickness based on the present simulation conditions.