Droplet impacting a superhydrophobic mesh array: Effect of liquid properties

Generation of monodisperse droplets by a large droplet impacting a mesh array is a common technique in microfluidic engineering, materials science, and drug production. Understanding the dynamic mechanism behind this is critical to controlling this process. This work uses a nonorthogonal multiple-relaxation-time lattice Boltzmann (LB) method to simulate a droplet impacting a mesh array. By varying the droplet viscosity and surface tension, a comprehensive parametric study is carried out to investigate the influence of droplet properties on the dynamic process of droplet impact, penetration, and fragmentation. The results indicate that the inertial effect dominates the spread stage of droplet impact. At later stages, the viscous drag and surface tension act to prevent the spread of the droplet, which results in different maximum spreading diameters. The penetration of the droplet through the mesh initially leads to the formation of a liquid jet, the length of which is determined by the competition between the dynamic pressure and capillary pressure. Different jet breakup lengths are observed for various Weber numbers. The maximum spreading diameter and jet breakup length are predicted by an extended model over a wide range of liquid properties, in good agreement with the LB simulation results. An analysis is also conducted from an energy perspective. It is found that the surface energy significantly decreases after the fragmentation of the high-viscosity droplet, which is caused by the merge of satellite droplets after the jet breakup.