Research On Condensation And Heat Transfer Performance On Superhydrophobic Surfaces

Condensation process on superhydrophobic surfaces plays an indispensible role in daily life and industrial application.For instance,fog harvesting and self-cleaning are beneficial aspects of the phenomenon.Dropwise condensation occurs on the surfaces which have lower surface energy.In this paper,condensation process and its heat transfer performance on superhydrophobic surfaces are focused.There are two ideas on the preparation of superhydrophobic surfaces.One is fabricating micro structures,and another is reducing surface energy.In this paper,some micro-scale pillars on silicon wafer were created with photolithography and ion etching technology.And then,an OTS coating was implemented on the substrates.The contact angle and sliding angle of the water droplet on the superhydrophobic surface were measured.It is found that the surfaces with micro pillars and OTS coatings show good hydrophobic properties.This paper also experimentally studies the condensation behaviors and on various silicon surfaces with micro-pillars inside a condensation chamber where humidity and temperature are controlled.The individual droplet growth rate,surface coverage are compared between the silicon wafers with different roughness.The results show that the variation frequency of droplet nucleation,growth and departure on the surface of smooth silicon is the fastest,which show inverse situations on the sample with the greatest value of roughness.In addition,the comparison of contact angle of the samples between after and behind condensation.The contact angle on the surfaces with micro-pillars reduces in comparison of that behind condensation on account of occurring the wetting mode transition from cassie to wenzel.Finally,the model of heat transfer on the superhydrophobic surfaces was studied.This paper introduced the model of individual droplet heat transfer and proposed a model to predict the value of the critical radius of departure on the vertical wall in Wenzel mode by experimental results.