A distributed air microbubble generator can produce microbubble solutions of uniform bubble diameter and high concentration. Two-phase fluid mixers of rotor-stator structure are usually used for generating microbubbles by distributed air. The structure design of its stator and rotor depends on the composition of two-phase medium to disperse. Both the stator and the rotor have independent effects on the characteristics of the two-phase fluid mixing device.
Rotor-stator mixers are of several types including the Silverson mixer, which is often used for homogenization and dissolution in liquid-liquid two-phase fluids. However, it reveals some defects in gas-liquid two-phase fluid mixtures. It is because the viscosity of gas-liquid two-phase fluid is relatively low compared to liquid-liquid two-phase fluid and the difference in gas and liquid density is very large. It is also because gas dispersion in the liquid is very difficult, and the conventional rotor-stator mixer configuration cannot provide sufficient pressure gradients in the shear gap, an important indicator of microbubble generation, due to the self-characteristics of gas-liquid two-phase fluid flow.
In order to increase the pressure gradient in the shear gap, Cha Su Song, a researcher at the Nano Physics Engineering Institute, has proposed a stator structure with a shear blade and rotor-stator engagement relationship. Then, he has evaluated the bubble diameter distribution formed in gas-liquid two-phase fluid flowing through the generator by the CFD-PBM method and compared it with experimental results.
Both the rotor and stator are of a shear blade structure. He analyzed the bubble diameter distribution in the fluid analysis program ANSYS Fluent 18.1. Then, he built a microbubble generator with the same structure as in the analysis and did some experiments. After that, he measured bubble diameter distribution by zeta potential analyzer (Malvern Zetasizer Nano ZS) and compared it with the analytical results.
The average bubble diameters obtained by CFD analysis and experiments were about 107nm and 113nm, respectively, which were in good agreement. In conclusion, the improvement of stator structure in the distributed air microbubble generator has a significant effect on generator characteristics.
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