An investigation on the effect of divergent angle on performance of Venturi-type bubble generators
In sewage treatment engineering, fine bubbles are often involved in promoting biochemical reaction processes in various aerated bio-reactors. Bubble size and its distribution are key parameters for evaluating the performance of a bubble generator. Size distributions of bubbles produced by Venturi-type bubble generators with different divergent angles (7.5°, 10.0° and 12.5°) were measured and compared in current work. Effects of the liquid and gas flow rates on the bubble size were also discussed. It is showed that the bubble size distributions followed a log-normal distribution. A larger divergent angle or liquid flow rate led to more smaller bubbles with larger number density being generated by the generator. The averaged bubble diameter has a −1.2∼−1.4 power dependence on the liquid Reynolds number, and has a −0.6∼−1.2 power law dependence on the divergent angle when liquid Reynolds number varied from 4.9 × 104 to 1.4 × 105. Gas Reynolds number has little effect on bubble size with void fraction varied from 0.02% to 1.5%. Moderately increasing the divergent angle is an effective method to obtain smaller bubbles.