Flow of bubbles through nozzles

Abstract One of the fundamental objectives in the mathematical modeling of two-phase flow is to understand and to formulate the interaction forces between two phases. For this purpose a well-defined two-phase flow situation, flow of bubbles through nozzles, was set up in the laboratory. A range of liquid flow fields was set up by flowing water through nozzles. Individual bubbles were injected into the water stream and their trajectories were recorded to provide data for evaluation and comparison with theories. Because of the limitations of the conventional photographic method of recording the bubble path, a computer-based optical system was designed for fast data acquisition. The optimal system works on the principle of the interruption of a light beam by a bubble passing between a sheet of light and a row of phototransistors. The bubble position (horizontal as well as vertical) along the nozzle is determined by its crossing through the light path to several rows of phototransistors attached to the nozzle. The performance and accuracy of the optical system were tested under various known physical situations. All the tests showed that the optical system is competent and effective in studying the motion of bubbles flowing through nozzles. A mathematical model was set up to predict the bubble motion. The various forces included in the model are the drag force, the apparent mass force, the buoyancy force, the bubble expansion force and the history forces. Comparisons between experiments and theories were made through a “point-to-point” numerical testing procedure. Results show that the bubble trajectory can be reasonably predicted (within 10% accuracy) by an equation of motion which includes a suitable drag force (dependent on relative velocity) and an apparent mass force (proportional to relative acceleration). Suggestions regarding the further improvement of the theory are also made.