Fine Bubble Generation with Venturi Tube Under High Gas–Liquid Ratio Condition: Structure Optimization and Bubble Size Prediction

To achieve efficient bubble refinement under high gas–liquid ratio (GLR) conditions in industrial applications, this study investigates the effects of Venturi geometry parameters and operating conditions on bubble size distribution under high GLR conditions. Experiments were conducted with throat velocities ranging from 4.34 to 13.02 m/s and GLRs from 10% to 60%, examining the effects of throat diameters (4 mm and 8 mm) and divergent angles (7.5°, 10°, and 12.5°). A novel baffled Venturi bubble generator was designed by maintaining constant throat flow area and principal parameters. Results showed that Venturi tubes with an 8 mm throat diameter produced smaller bubble sizes at higher liquid flow rates. In contrast, excessively large divergent angles produced unfavorable larger bubble sizes due to higher GLR and flow separation. Based on experimental data (Reynolds number range: 12,163–106,084), a comprehensive bubble size prediction model was established, which simultaneously considers the effects of throat diameter and divergent angle. Increasing the liquid flow rate and reducing the GLR effectively minimize bubble size, while the newly developed bubble generator demonstrates superior performance compared to conventional Venturi designs. These findings provide practical references for the design and industrial application of Venturi bubble generators under high GLR conditions.