Experimental Investigation of Microbubble Evolution in the Liquivac Multiphase Flow Pump

This paper aims to experimentally investigate the mechanisms of microbubble characteristics evolution within an axial pump. The findings will aid in assessing the pump performance by identifying the range of bubble sizes and comparing them with the threshold size (<300 µm). This study also provides evidence supporting the use of such pumps as microbubble generators for large-scale applications, such as aquaculture farms and dissolved air flotation (DAF) in water treatment processes. The temporal and spatial characteristics of microbubbles were analysed at water flow rates of 16.7, 33, 50, 67, and 83 L/min, and air volumetric qualities (β) ranging from 10% to 40%, at a pump rotational speed of 2900 rpm. High-speed photography and image processing techniques were employed to record 200 video frames (around 6 second) to analyse them in order to determine the mean microbubble size and distribution. The main findings include: i) bubble size decreases along the axial direction from the pump inlet to the outlet; ii) microbubble size decreases with higher water flow rates and increases with higher air volumetric qualities; iii) increased impeller rotation, at constant water flow rate and air volumetric quality, reduces microbubble size.