Fabrication Of Superhydrophobic Surfaces On Metallic Substrates And Study Of Gas-Liquid Two-Phase Flow In Micro/Mini Channels

A simple and convenient technique for fabricating superhydrophobic surfaces is developed. Super-hydrophobic surfaces on Aluminum, Aluminum alloy and Zinc substrates are prepared in this work by constituting metal surface with acidic etching and subsequently decreasing the surface energy with fluoroalkylsilanes coating. The as-prepared surfaces show water contact angles of larger than 150°, as well as roll off angels of about 5° (5-μL droplet). The resultant surfaces are characterized by means of scanning electron microscopy (SEM). The results show that a "toy bricks" structure forms on the superhydrophobic surface of aluminum and aluminum alloy substrates and microscale crystal and fine nanogrooves structure forms on Zinc substrates. Both of them are hierarchical roughness structures of unitary self-similarity. The experimental results demonstrate that the surface microstructures are the key to the preparation of superhydrophobic surfaces. Effects of different parameters on contact angles are investigated. And the chemical structures of the superhydrophobic surface are analyzed.The channel with superhydrophobic surface is structured and some fancy phenomena such as "ladder configured flow", turning flow and sinusoidal flow are observed when water flowing in a rectangular channel constructed with one superhydrophobic wall and one super hydrophilic wall in the opposite side. The existence of shear-free nano-air layer at the fluid-solid boundary is the essential reason for these fancy phenomena.Experiments of air-water two-phase flow are performed in 1-5mm glass tubes at atmospheric pressure. The experimental results together with large amounts of observation judgment are used to ascertain the flow patterns of horizontal and vertical upward flow in micro/mini channels. Flow pattern transition is described in detail and flow maps were drawn respectively. It is found that the flow maps drawn in this study are basically coinciding with previous published ones. Furthermore, distinguishing flow patterns by pressure fluctuation is attempted and the results show it is feasible.