Theoretical and experimental investigation of quasi-steady-state bubble growth on top of submerged stainless steel nozzles

This study investigates bubble growth on submerged 0.11–0.84 mm diameter stainless steel nozzles under quasi-steady-state both theoretically and experimentally. The bubble shape and an analytical formula for the bubble volume during growth are derived based on a force balance method, which includes the effect of the surface tension, buoyancy and gas/liquid hydrostatic forces, as well as the pressure rise due to the effects of gas flow rate. Experiments are conducted under low gas flow rate conditions (0.015–0.83 ml/min) on three different-sized orifices with bubble growth recorded by a high speed optical camera. Detailed characteristics related to bubble growth such as the variation of the instantaneous contact angle, radius of contact line, radius at the apex of the bubble and bubble height are obtained. The shape of the bubble is in excellent agreement with predictions of the Young–Laplace equation, and the derived analytical bubble volume predicts experiments well under the flow rates investigated here. The waiting and bubble formation time are found to be non-monotonic with orifice diameter. A multistage bubble growth scenario is identified and found to be controlled by the motion of the contact line, as well as by the inter-play between various acting forces.