Effects of surfaces wettabilities on horizontal falling-film flow pattern

It is significant to study and regulate the inter-tube falling film flow pattern for the heat transfer of falling film devices. In this paper, the effect of surface wettability on the flow pattern is considered using three different tubes, super-hydrophilic and hydrophobic, includes hydrophilic tubes for comparison. Visual experiments and theoretical analysis are performed to study the effects of wettability on inter-tube flow pattern. The results show that staggered and inline column patterns are remarkably affected by the surface wettability. For super-hydrophilic and hydrophilic surfaces, only staggered column mode can be found for water. But for hydrophobic surfaces the inline column pattern occurs. In addition, there is a upper thread contact angle for staggered column mode, and the critical value is 67°. While for inline column mode, the minimum contact angle exists, and the critical angle is 106°. © 2016, Science Press. All right reserved.