Pool Boiling And Anti-fouling On Hydrophobic Coatings Prepared With Chemical Etching

In this paper, rough TiO₂-FPS composite hydrophobic surfaces were prepared on AISI 304 stainless steel substrates in order to study the influence of chemical etching process on the pool boiling heat transfer and fouling characteristic. The influence of processing parameters on the morphology and hydrophobicity of surfaces were studied and favorable etching condition was found. The structure and property of the material surfaces play important roles in the pool boiling, thus in this paper, chemical etching and liquid phase deposition techniques were utilized to fabricate fine hierarchical micro- and nano-structured surfaces on stainless steel substrates, and the surfaces were further modified by the low surface free energy agent of Fluoroalkylsilane. It has been found that the chemical etching process can build porous rough structure on surface, and significantly improve hydrophobicity of composite coatings. The heat transfer and fouling resistance performance of different surfaces were studied in pool boiling device. The results showed that chemical etching process can obviously enhance the heat transfer performance. The chemical etched coatings showed about one time enhancement in heat transfer coefficient over polished SS surface. And the fouling experiments in CaSO4 solutions indicated that coating surfaces can reduce fouling resistance of heat transfer surfaces. When the heat flux is 50.69 kW·m-2,and the concentration of CaSO4 solution ranged from 1.8 to 2.1 g/L, the anti-fouling performance of hydrophobic surfaces on smooth and chemical etched substrates were investigated. The chemical etched coating surfaces showed about 18% of fouling resistance than that of smooth substrate, while still exhibited more than 60% anti-fouling enhancement than polished stainless steel surfaces. On the one hand, the rises on rough surface provided more adhension position for fouling particles and accelerated fouling deposition. On the other hand, surfaces with low free energy can inhibit fouling deposition,thus enhance the anti-fouling performance of surfaces. Namely the results above due to the combination effects of surface roughness and surface free energy.