Effects of orifice height and gas flow rate on underwater bubbles dynamics in crossflow

Abstract

This study employs high-speed photography and image processing to investigate the effects of orifice heights ($H_n/\delta$ = 0, 0.5, and 2, where $\delta$ represents the boundary layer thickness) and gas flow rates (Q_g = 0.5, 2, and 10 L/min) on bubble dynamics in crossflow. Results indicate that higher gas flow rates extend bubble formation time, enlarge the bubble diameter, increase the terminal rising velocity, and reduce the trajectory inclination angle. Additionally, greater orifice height accelerates liquid flow at the orifice. This acceleration leads to earlier bubble detachment, which reduces the bubble diameter, increases the trajectory inclination angle, and lowers the terminal rising velocity. Furthermore, a mathematical model was developed to comprehensively describe the entire process of bubble formation and rising, accurately predicting kinematic parameters such as bubble velocities and the forces acting on the bubble. In the formation stage, the model agrees well with experimental data (error ∼ 10%), identifying buoyancy $F_B$ and mass-related inertial force $F_{Imx}$ as the dominant detachment force in rising and streamwise direction, respectively. In the rising stage, the model incorporates a terminal velocity correction to account for the impact of preceding bubbles, significantly enhancing accuracy (error < 7%). It identifies $F_B$, suction from preceding bubbles $F_w$, and drag $F_{Dy}$ as the key factors affecting the rising velocity. Meanwhile, forces in the streamwise direction are minimal as the terminal streamwise velocity approaches the incoming flow velocity. These findings significantly enhance our understanding of bubble dynamics under crossflow, providing valuable insights for optimizing industrial processes involving gas-liquid interactions.