Effect of throat diameter on the cavitation phenomenon inside an aerated Venturi tube for microbubble production

Aeration in Venturi tubes for microbubbles production has become popular in recent years as it enhanced the transportation of oxygen and other gases in wastewater treatment and mineral engineering. In an aerated Venturi, air/gas was injected upstream into the flowing liquid inside the Venturi tube. The air flows inside the Venturi tube as bubbles, before breakup occurs downstream after the throat area. This method promoted the transportation of particular gases or substances in microbubbles. To further increase the generation of microbubbles, flowing liquid velocity was increased by decreasing the throat diameter, but cavitation started to emerge inside the tube as velocity increased. This present study aims to investigate the effect of reducing the throat diameter on the cavitation number of the aerated Venturi tube and how it affects the breakup characteristics of bubbles. Activities involved in the investigation were: visualization of flow and generated microbubbles, image processing of the images captured, pressure and void fraction measurement, and calculating the cavitation number. The result showed that reducing the throat diameter initiated the cavitation occurrence earlier, and in aerated cases, cavitation exists in the form of cavitated bubbles. Aeration also affects the cavitation number in a non-cavitated flow but does not significantly affect the existing cavitated flow. Reducing the throat diameter also successfully increased the generation of bubbles less than 0.2 mm, but the overall SMD did not show a straightforward relationship with cavitation number.