Author(s): Arsalan Behzadipour; Amir Azimi

Linked Author(s): Arsalan Behzadipour

Keywords: Bubble plume; Air-water mixing; Bubble dynamics; Bubble size; Bubble velocity

Abstract: Bubble plumes are an example of multiphase flow, which can be used in nature-like aeration tanks and as gas diffusers for lake aeration. A set of experimental tests was carried out to investigate the effects of grid-screen in vertical bubble plumes with different nozzle sizes and airflow discharges. Two nozzle diameters of 1 mm and 3 mm and two airflow discharges of 4 L/min and 6 L/min were selected for this study. A grid-screen with different grid openings was installed at the center of the bubble plume and at different elevations from the nozzle (Xs = 0.14 m, 0.22 m, and 0.30 m) to study oxygen transfer enhancement and mixing capacity of bubbles. The effects of grid-screen openings, distance from the nozzle, and airflow discharge on variations of bubble characteristics were examined. A Refractive Bubble Index (RBI) probe was used to measure bubble diameter, bubble size distribution, bubble concentration, interfacial area, and the centerline velocity of bubbles. Experimental results indicated that increasing the distance between the grid-screen and the nozzle increased the bubble concentration by 9% and reduced the bubble size by 31%. It was found that the size of grid-screen and its distance from the nozzle in high air discharge of 6 L/min decreased the vertical velocity of bubbles by 38%. The results showed a direct correlation between the airflow rate and the total number of air bubbles in bubble plumes with a grid-screen. Moreover, bubble velocity hindered by the grid-screen and gradually increased after a distance from the grid-screen. By installing a grid-screen at 0.3 m above the nozzle, the time-averaged bubble concentration increased by 18% and the time-averaged bubble velocity decreased by 31% in comparison with a benchmark test without a grid-screen.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022695

Year: 2022