Analysis of Flow State in Venturi Tube for Fine Bubble Generation

Abstract

Bubbles with a diameter of 100 μm or less are called fine bubbles, which have been applied widely in the industrial fields due to its strong detergent, bactericidal effect, and bioactivity. Ballast water is the seawater to stabilize the center of gravity of a ship. In water purification, a technology has been developed to reduce the dissolved oxygen (D.O.) concentration and pH by mixing water with gas to deaerate D.O. and dissolving CO2, but gas is mixed with such water. When purifying water quality, it is important to reduce the bubble diameter when gas is mixed with water, and to improve the efficiency of dissolving CO2 by degassing D.O.. In this research, a method to improve the mixing efficiency of ballast water treatment equipment by improving the fine bubble generation efficiency of the venturi tube is investigated by experiment and simulation analysis. We design venturi tubes with different divergent angles and investigate the optimized geometric combination by experiment and numerical simulation for improving the fine bubble size and volume. From the experimental results, we find that in the nozzles with small divergent angles the low pressure region becomes longer and the pressure recovery slows down, which promote the breakup of bubbles. The simulation results show that in the nozzles with the divergent angles of 15°and 20°, the affection region of gas-liquid two-phase flow becomes larger, and the concentration of bubbles near the wall or near the center of the nozzle will promote the breakup process of bubbles.