The Breakup Characteristics of Bubbles in Venturi Tubes Under Different Levels of Dissolved Gas

抄録

Venturi tube is a microbubbles generator with simple and robust design. Air was injected into the liquid flow, transported through the throat of the Venturi tube and break up as microbubbles in the diverging area. In high-speed liquid, cavitation occurred along with the air transported to the throat of the Venturi tube. One of the factors that affected cavitation existence is dissolved gas level in the liquid. Therefore, this study aims to compare the microbubble collapse phenomena under different dissolved gas level to further understand the effect of cavitation to microbubbles formation. In this experiment, two different dissolved oxygen level (DO) were used to represent the dissolved gas level in the liquid. The result showed that although breakup mechanism was generally the same for both DO level, higher DO at high liquid speed had more wrinkles on its bubbles surfaces during the bubbles breakup process. Pressure measurement results at higher liquid speed demonstrated that DO 8.5 mg/L had slightly higher inlet pressure than DO 6.5 mg/L for the same gas flow condition. Calculation on bulk cavitation number and pressure loss coefficient suggested cavitation occurrence at higher liquid speed and higher air flow ratio. Higher DO have slightly higher pressure loss coefficient under the same bulk cavitation number. On the other hand, bubbles number distribution results showed that higher DO condition produced more bubbles than lower DO specifically at higher liquid speed with low and medium air flow ratio. Calculation of SMD for different DO at high liquid speed resulted in a slightly smaller bubbles diameter at low and medium air flow ratio of higher DO while the value is almost the same for high air flow ratio. At low liquid speed, higher DO have smaller SMD value for all air flow ratio cases.