Gas injection from slot nozzles with various shapes in water

Results of experiments examining behaviour of gas bubbles detouching from slot nozzles of various shapes are presented. Gas was injected into water through the slot nozzles of 200 mm in length and 0.05, 0.1 mm in width. Four types of the slot nozzles were used: (a) flat nozzle, (b) mountain-shaped nozzle, (c) valley-shaped nozzle, (d) unilaterally inclined nozzle. They were made of Teflon which is poorly wetted by water. The bubble behavior is described by two parameters: bubble diameter formed at the slot nozzle and the number of bubble sources. It was found that the gas injection through the mountain-shaped nozzle produces the smallest bubble while the largest bubble is formed when the valley-shaped nozzle is used. Bubbles produced at the flat nozzle and unilaterally inclined nozzle were almost the same in size which is intermediate between the bubble sizes for the mountain-shaped and valley-shaped nozzles. Comparative experiments showed that, when gas is injected through a wetted slot nozzle, the bubble size is much smaller than that for the nonwetted slot nozzle of the same design (flat nozzle) at lower gas flow rates. For all experiments, the bubbles become smaller as the number of bubble sources increased.