EFFECT OF HYDROPHOBICITY ON DEWETTING OF LIQUID FILM OF TWO-PHASE FLOW IN A HORIZONTAL TUBE

Abstract

A study on the effect of hydrophobicity on dewetting of the liquid film of two-phase water-air flow in hydrophobic macro-channels (4.76 mm i.d.) was presented here. The tube material is fluorinated ethylene propylene (FEP) which has an inborn hydrophobic property with contact angle 96.08°. To increase the hydrophobicity of the channel, the channel surface was treated by sandpaper number grit 400, 320, 100, and, 80 to develop micro structured surface forming the air layer below the water droplet which increased the contact angle due to decreased surface energy. The measured contact angle was 109.97°, 111.87°, 121.94°, and, 125.27° in order of increasing hydrophobicity. The two-phase flow of the channels with different contact angles was visualized by a high-speed camera and the flow pattern maps were constructed with superficial velocity and modified Weber number as axis. In the flow pattern map, according to the appearance of the dewetting of the liquid film, the flow pattern was classified into two-types, wet condition and dry condition. It is observed that the increased hydrophobicity affects the transition of wet-dry flow boundary and flow pattern boundary. Modified Weber number which is a ratio of fluid’s inertia to work of adhesion was used to analyze the effect of the hydrophobicity on flow pattern map in two-phase flow.