International Journal of Heat and Mass Transfer, Vol.132, 1105-1115, 2019
Reduction in the contact time of impacting droplets by decorating a rectangular ridge on superhydrophobic surfaces
Increasing attentions have been paid to the reduction in contact time between rebounding droplets and solid surfaces because of its potential applications in self-cleaning, anti-icing, anti-dew, and so forth. Owing to the axisymmetric spreading/retraction dynamics of impacting droplets on flat surfaces, there is a minimum contact time. Recently, adding a cylindrical wire or a triangular ridge on superhydrophobic surfaces has been proven to be an effective approach to break through this limit. Here, via lattice Boltzmann simulations, we show that droplets impacting superhydrophobic surfaces decorated with a macro rectangular ridge can also yield a significantly reduced contact time. Based on the simulated snapshots of impact dynamics, we reveal that the presence of the rectangular ridge can induce a tunable nonaxisymmetric spreading/retraction dynamics. We found that once an impacting droplet is split into two fragments by the ridge, the contact time will be lower than the limit achieved on the flat surfaces with the same contact angle. We observe three different retraction ways for the split fragments depending on impact Weber number (We) as well as ridge height and width. When the formed fragments only retract once before they rebound from the surface, a lower contact time can be achieved. However, if they retract twice or re-coalesce after retracting once, the contact time will increase. We demonstrate that a maximum 48% reduction in contact time can be reached on the ridged surface at We = 29.6. (C) 2018 Elsevier Ltd. All rights reserved.