Figure 3. Effect of the diameter and type of the release pipe on the particle size distribution of microbubbles
The size distribution of microbubbles in straight and bend pipes with the same length was shown in Fig. 3(C). The particle size of microbubbles in the straight release pipe is concentrated between 20~60 μm, and the peak value appears at 40 μm. While the microbubbles generated in the bend pipes are concentrated in 40~80 μm, and the peak frequency distribution is 55 μm. The cumulative curve of microbubble particle size shows that the proportion of microbubbles with particle size less than 50 μm (65%) generated in the straight release pipe is 20% higher than that of the bend type (Fig. 3(D)). In conclusion, the microbubbles generated by the straight release pipe have small particle size and concentrated distribution range. When the microbubble moves in the straight pipe, it is only subject to the resistance along the way, while when it moves in the release pipe with an elbow, it is also subject to the local resistance generated by the elbow in addition to the resistance along the way, resulting in the loss of microbubble pressure in the pipe, making the microbubble particle size larger. Besides, the elbow increases the turbulence intensity of the fluid, which increases the collision probability in the process of microbubble movement, resulting in the rupture or merger of microbubbles, and the particle size of microbubbles becomes larger.