BUBBLE FORMATION IN A COFLOW CONFIGURATION IN NORMAL AND REDUCED GRAVITY

A study of bubble generation for constant gas-flux condition by single -nozzle injection in a coflowing liquid is reported. Focusing on singl e-bubble generation in the dynamic and bubbly flow regime, the onset c ondition for bubble coalescence is investigated The role of various fo rces involved in the bubble formation process is studied and an overal l force balance describing bubble dynamics is developed Gas-momentum f lux and buoyancy in normal gravity enhance, while the surface-tension force at the nozzle rim inhibits bubble detachment. On the other hand, liquid drag and inertia can act both as attaching or detaching forces , depending on the relative velocity of the bubble with respect to the surrounding liquid. Predictions of the theoretical model compare well with the present reduced-gravity experiment and available normal-grav ity experiments. Effects of the fluid properties, injection geometry, and flow conditions on bubble size are investigated.