MODEL-BASED EXPERIMENTAL ASSESSMENT OF THE FORCES ON A BUBBLE WITH DIFFUSION CONTROLLED GROWTH

摘要

Prediction of, for example, bubble radius at detachment and bubble trajectories require knowledge of the forces exerted on the bubble. The present study aims at experimental validation of a Lagrangian model for the hydrodynamic forces exerted on a vapor bubble that is growing with the shape of a truncated sphere in uniform approaching flow. A dedicated experimental set-up has been designed so that the flow that approaches the bubble is practically uniform. A novel bubble generator, with a constant temperature at the base where the bubble is formed is positioned in the center of a vertical tube. A high-speed camera has been used for filming bubble growth and detachment from two sides simultaneously. The deformation at detaching bubbles has been quantified using 3D reconstructions of the bubble shape. Histories of the bubble radius and main axes are measured. Main non-hydrodynamic force components in the direction perpendicular to the vertical wall have been determined from measured quantities. The sum of these forces should equal the hydrodynamic force that is independently assessed using model predictions and measured parameter histories. This comparison is made. A sensitivity analysis is performed of all individual force components. Some errors are compensating each other, other errors have quite some influence on the final accuracy of the force determinations.