Investigation of frosting and defrosting on superhydrophobic surface

Abstract

Frosting and defrosting on superhydrophobic surface have been investigated. For comparison, specimens with different wettability are prepared for the experiment including superhydrophilic surface, hydrophilic surface, hydrophobic surface and two superhydrophobic surfaces with different nano-structure. From the investigation, the density of frost gets higher and energy barrier for nucleation gets lower as the contact angle gets lower. The weight of frost layer over unit area is recorded according to time. It is found both superhydrophobic surface and superhydrophilic surface can reduce the amount of frost due to nucleation process and initial frost structure which are influenced largely by surface energy. During the defrosting process, there was water remaining on the samples except the SPA (silanized porous aluminum) superhydrophobic surface. A thin uniform water film was left on the superhydrophilic surface due to its superhydrophilicity. Droplets adhere to the polytetrafluoroethylene (PTFE, Teflon R AF 601 S2, 6 wt%,DupontTM) nano-fiber superhydrophobic surface due to the flexibility of its textile PTFE nano-fiber structure. Water contact state is changed from Cassie-Baxter state into Wenzel state after defrosting. As the nano-structure on the SPA superhydrophobic surface is rigid and multi-scale porous, it could be free from water adhering after frost melts. This finding indicates the potential application of SPA superhydrophobic surface as an effective defrosting method which has higher supercooling degree and frost reduction effect and could be free from water adhering during the defrosting process.