Numerical and theoretical study on the spreading characteristics of droplet impact on a horizontal flowing liquid film

Abstract

Droplet impacts on moving films involve many industrial applications. However, limited numerical and theoretical work has been performed to study droplet impact on flowing films. In this paper, the influence of the thickness of the moving liquid film on dynamic characteristics of a single droplet impact was studied by the CLSVOF method. An analysis of the velocity field, pressure field and vorticity cloud diagram inside the liquid showed that as the liquid film thickness increased, the migration distance of the asymmetric crown, the amount of liquid flowing into the crown wall and the angle between the crown wall and the liquid film all increased. Moreover, based on the conservation of mass and momentum, the mathematical model of droplet spreading was extended to a moving liquid film for the first time, which has a wider range of applications, and the mathematical model was also verified by combining the numerical and experimental results. The spreading velocity of the droplet on the moving liquid film is exactly equal to the average of the upstream and downstream spreading velocities; the relationship between the spreading diameter and contact time is a power-dependent trend with a power index of approximately 1/2, and with increasing liquid film thickness, the power index increases slightly. This study not only extends the kinetic theory of droplets impinging on a liquid film but also provides guidance for practical processes such as spray cooling and impinging stream chemical synthesis.