| Summary: | The present experimental study aimed to investigate the performance and characteristics of the dissolved oxygen in water aeration under the variations of the gap between the air nozzle and the outlet of new developed swirl flow type of the microbubble generator (MBG). The present experimental investigation, the flow rates of both of air (QG) and the water (QL) were determined in the range of (0.1–0.8) l/min and (20–50) l/min, respectively. The shadow photographic technique was used to extract the results of a high-speed camera of microbubbles images to find the bubbles size and their distribution. The dynamic physical absorption model was used to measure the coefficient of the oxygen volumetric mass transfer (KLa). The results show that the microbubbles size (diameter average davg and peak PDF curve) produced by the swirl MBG type was smaller and more uniform than that of produced by orifice MBG type. Next, the characteristics of the microbubbles were investigated by the combinations of QG, QL and the gap between the air nozzle and the outlet of the microbubble generator. Here, it is noticed that the higher the gas flow rate, the higher the average diameter of the bubble. The higher the liquid flow rate, the lower the average diameter of the bubble. Furthermore, the QL increases with KLa. Finally, the empirical correlations to predict the KLa, davg and the log-normal distribution of the bubble diameter were proposed.
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