STUDY ON BUBBLE BREAKUP BEHAVIOR IN A VENTURI TUBE

Abstract

We focus on a venturi-tube-type micro-bubble generator that can generate tiny bubbles with a diameter of 10 µm−1 mm in a high gas volume flow ratio. However, the mechanisms of micro-bubble generation are not clarified. The objective of the present study is to reveal the mechanism of the bubble breakup phenomenon. In order to achieve the objectives, we observed bubble behavior in a venturi tube in detail, and measured the pressure and void fraction profiles in the flow direction. By using the measuring results, the gas−liquid mixture velocity, sonic speed, and Mach number were estimated. In the experimental results, the bubbles expanded once into a divergence region of the venturi tube and then contracted rapidly and broke up into a great number of tiny bubbles. The pressure decreased sharply around the throat of the venturi tube and increased at the bubble breakup region. On the other hand, the void fraction increased downstream from the throat and decreased around the bubble breakup point. These results indicate that the flow was supersonic flow between the throat and the bubble breakup point, while it became subsonic flow downstream from the point. Therefore, it was proposed that a shock was present at the bubble breakup point.