3D kinematics of cavitation bubbles and the relationship with cavitation intensity in straight-tube ultrasonic microreactors

Abstract

Straight-tube ultrasonic microreactor has notable advantages in nanomaterial preparation. The 3D kinematics of cavitation bubbles impacts its mixing efficiency, which is critical for understanding and optimizing the reactor. High-speed photography, image processing, sonochemical luminescence, degradation of chlorinated hydrocarbons, fatty emulsification, etc., were used to study the 3D motion of cavitation bubbles and intensity. In the channel with a 1–2 mm inner diameter, a few macrobubbles moved along the glass channel, and cavitation bubble clouds were almost unobserved, resulting in lower cavitation intensity and poor emulsification efficiency. At 3–5 mm, bubble clouds were divided into 2–4 segments with a radial-circulation motion. Consequently, both cavitation intensity and emulsification were significantly improved. Moreover, macrobubbles escaped radial circulation, and moved rapidly near walls, but were confined in segments. At 6 mm, the bubble clouds adhered to one side wall, and overall cavitation intensity was similar to 4–5 mm channels.