Bubble formation in a coflow configuration in normal and reduced gravity

Abstract

Abstract A study of bubble generation for constant gas‐flux condition by single‐nozzle injection in a coflowing liquid is reported. Focusing on single‐bubble generation in the dynamic and bubbly flow regime, the onset condition for bubble coalescence is investigated. The role of various forces involved in the bubble formation process is studied, and an overall force balance describing bubble dynamics is developed. Gas‐momentum flux 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‐gravity experiments. Effects of the fluid properties, injection geometry, and flow conditions on bubble size are investigated.