Experimental investigation on proper use of dual high-low frequency ultrasound waves—Advantage and disadvantage

An experimental study was conducted to investigate the proper use of dual frequency ultrasound irradiation in sonoreactors. For this purpose, two waves with frequencies of 1.7 MHz and 24 kHz were combined. A dual frequency rig was equipped with a high frequency 1.7 MHz ultrasound transducer and a low frequency one generating 24 kHz waves. Dushman competitive reactions were used to study micromixing, Weissler reaction for evaluating cavitation activity and ammonia degradation experiment to investigate the superposition effect of two coupling waves on decomposition strength. The results revealed that combining these waves has a positive effect on number of generating cavitation bubbles and micromixing performance. However, this combination reduced the strength of the low frequency wave and diminished the ammonia degradation process efficiency. The micromixing enhancement in terms of the segregation index in dual frequency irradiation mode is approximately 46.9% and 40.1% more than single low and high frequency irradiation, respectively. On the other hand, the ammonia removal efficiency is reduced by 10.3% in dual frequency irradiation compared to single low frequency layout.