Dynamics of bubble growth and detachment in a shear flow

The prediction of heat transfer coefficient in convective nucleate boiling remains an open question. Advanced models are based on heat flux partitioning taking into account the contribution of phase change, rewetting of the wall after bubble lift-off or in the wake of the sliding bubble, convection between the nucleation sites. These models require a good prediction of the diameter and frequency of bubble detachment. In this context, specific experiments on isolated bubble nucleation and growth are performed in a shear flow in horizontal channels and in microgravity conditions. High-speed video images and image processing allow to determine the geometrical characteristic parameters of the bubble: bubble equivalent radius, height, position of the center of gravity, width of the bubble foot and contact angles on both sides of the bubble. From these data, the forces acting on the bubble are evaluated and those responsible for bubble detachment (buoyancy, drag and added mass forces) are identified. Recent results on air bubble injection in a shear flow have validated the expressions of the capillary force and the drag force in the case of a quasi-static bubble growth. The force balance model is a first step toward the prediction of the bubble detachment diameter. This approach has been successfully validated for air bubble injection in a shear flow. In the case of a boiling bubble, the growth is most of the time very rapid and the inertia force as added mass force has to be taken into account.