Numerical simulations of multi-hop jumping on superhydrophobic surfaces

Water vapor condensation on superhydrophobic surfaces has received much attention in recent years because of its ability to shed water droplets via coalescence-induced droplet jumping. However, the efficient removal of jumping droplets can be limited by droplets return to the surface due to gravity, entrainment in bulk convective vapor flow, and entrainment in local condensing vapor flow. The return droplet merged with others and induced multi-hop jumping, whose mechanism still remains poorly understood. In this work, a VOF simulation is carried out to investigate the multi-hop jumping. If the returned droplets contact the droplets on the surface before touching the surface, the returned droplet coalesce with the droplets on the surface in the air, which is not conducive to shrinkage and rebounding, and the intrinsic multi-hop jumping process is inhibited. The momentum of the returned droplets is transformed into the momentum of the jumping droplets, and the multi-hop jumping process is strengthened. The multi-hop jumping velocity is linearly related to the velocity of the returned droplet. When the droplet radius ratio is less than 0.615, the momentum generated by the intrinsic multi-hop jumping can be neglected, and the multi-hop jumping velocity can be predicted base on the velocity of the returned droplet. This work will provide effective guidelines for the design of functional SHSs with enhanced droplet jumping for a wide range of industrial applications.