Influence of solids motion on ultrasonic horn tip erosion in solid–liquid two-phase flows

Abstract

Ultrasound technology is a promising technique for wastewater treatment. However, its industrial application and scale-up face numerous problems, such as ultrasonic horn tip erosion. In solid–liquid flow systems, the synergy between cavitation and solid particle erosion is unclear, and the influence of solids motion is relatively unknown. By analyzing the tribosystem near the tip surface, we hypothesize that the synergistic erosion depends on the flux of solid particles flowing past the surface, relating to the local solids concentration and velocity. This hypothesis was investigated by ultrasonic cavitation–particle erosion tests performed in an eccentrically agitated tank. To study the effect of local concentrations and velocities, we carefully controlled the total solids and impeller speeds by integrating their coupled influence. Results indicate that synergistic erosion was aggravated at higher solids concentrations and velocities, and both parameters, based on a sensitivity analysis, show similarities in their relative degree of influence on erosion. This supports our hypothesis, which unifies the two parameters into a single factor, and explains the synergism in solid–liquid flows. Understanding these influencing factors and mechanisms will contribute to erosion prediction and the optimization of ultrasound applications in wastewater treatment processes.