Liquid flow transition and confined free film formation on a vertical plate with an open window

A novel element for gas–liquid contact, a plate with rectangular windows was designed to enhance absorption process. This paper describes some experimental observations of free-surface flows arising when thin liquid film flows through the window. Dozens of windows with different geometries and six fluids with Ka varying from 52 to 3000 were used to investigate the flow mechanism. Various free-surface flow patterns composed of droplets, columns, sheets and their combinations were observed in the window region with increasing liquid flow rate. At a critical flow rate, liquid film was able to full fill the window and unique wavy trains were observed (named as twin-liquid films). To characterize the film formation conditions, an empirical equation based on experimental data was proposed. Hysteresis phenomenon was manifested by obviously different flow rate for the film formation and breaking. Multiple and dynamic flow structures shown here would broaden traditional knowledge of liquid flow in packed columns and clarify the mechanism of mass transfer intensification for the perforated packings.