Effect of Contact Angle Hysteresis on Droplet Dynamic Behaviors for Hybrid Surface

Superhydrophobic-hydrophobic hybrid surface with different Contact Angle Hysteresis (CAH) in superhydrophobic region are prepared by controlling the etching time of NaOH and (NH4)2S2O8 mixed solution. Departure droplet diameters, sweeping period and drop size distribution of different surfaces are researched through experiments in this paper. Environmental Scanning electron microscopy(ESEM) results show that micro-nano structures of superhydrophobic surface become finer with the increase of etching time, which lead to the increase of CAH of the superhydrophobic surface. Two kinds of droplets drainage behaviors are observed in the condensation experiment: droplets suction horizontally and trans-regional droplets shedding. Superhydrophobic surface with larger CAH is more capable to aggregate the droplets on hydrophobic region thus enhance the renewal of condensation surface and heat transfer performance. Departure droplet diameters of trans-regional droplets decrease with the increase of CAH of the superhydrophobic region and the sweeping period has the same tendency. Compared with completely hydrophobic surface, droplets radius on hydrophobic region of hybrid surface are smaller, which are mainly distributed in 0-50 μm range. © 2017, Science Press. All right reserved.