Experimental study of the visualization of bubble breaking mechanism on the swirl type MBG output channel

This study aims to determine the mechanism of breaking bubbles into small size in a Swirl type microbubble generator (MBG) with variations in water discharge (QL) at the distance of the air nozzle to the MBG outlet of 1mm. Observations were made using a Phantom Miro M310 high speed video camera with a maximum resolution of 1200×800 to record the microbubble phenomenon. All measurements were taken at a frame rate of 3000 fps. The spatial resolution and frame rate used in this study allow the behavior of the microbubbles to be observed in detail. The focal length and lens aperture are 85 mm and 2.8 mm, respectively. The length between the lens and the viewing area is 350 mm. A wide measuring field and a narrow depth of field were obtained, which is about 2 mm. Its field of measurement is 40.3 mm x 85 mm, and it was found that the 1 pixel of the camera represents 89,55 µm. The results of the investigation showed that the mechanism of the bubbles breaking into smaller sizes starts with bubbly flow in the mixing chamber channel, then forming ligaments at the MBG outlet, before finally bursting into small bubbles. At higher QL and constant air flow (QG), more bubbles were produced and more uniform with smaller size.