Non-perturbing cavitation detection / monitoring in sonochemical reactors

Abstract

To optimize the ultrasound irradiation for cavitation based ultrasound applications like sonochemistry or ultrasound cleaning, the correlation between cavitation intensity and the resulting effect on the process is of interest. Furthermore, changing conditions like temperature and pressure result in varying acoustic properties of the liquid. That might necessitate an adaption of the ultrasound irradiation. To detect such changes during operation, process monitoring is desired. Labor intensive processes, that might be carried out for several hours, also require process monitoring to increase their reliability by detection of changes or malfunctions during operation.In some applications cavitation detection and monitoring can be achieved by the application of sensors in the sound field. Though the application of sensors is possible, this necessitates modifications on the system and the sensor might disturb the sound field. In other applications harsh, process conditions prohibit the application of sensors in the sound field. Therefore alternative techniques for cavitation detection and monitoring are desired. The applicability of an external microphone and a self-sensing ultrasound transducer for cavitation detection were experimentally investigated. Both methods were found to be suitable and easily applicable.

Self-sensing cavitation detection capability of horn geometries for high temperature application

“…An alternative method for the measurement of the cavitation frequency spectra is monitoring the electrical signals of the ultrasonic transducers used for excitation. In [12] a feasibility study for this technique has already been conducted. Here the signals of an external microphone, a hydrophone and the transducer's current signal are compared.…”

Self-sensing ultrasound transducer for cavitation detection

“…Neppiras applied the motional impedance of a focussed ultrasound transducer to analyze the movement of bubbles in 1976 [5]. More recently, a correlation between the onset of cavitation and indicators derived from the driving current signal of a piezoelectric transducer showed the feasibility of this method [1]. The advantage of this method is that it may be easily applied to various ultrasound systems as no changes on the system are required.…”

“…Thus, alternative methods are desired to quantify cavitation in situ without the necessity of applying sensors in the liquid. In a first feasibility study the feedback of cavitation on the driving signals of a piezoelectric transducer turned out to be a promising method [1]. This paper deals with a more detailed investigation of this method in a broader frequency range, and compares it broadband acoustic emission.…”

Closed loop cavitation control – A step towards sonomechatronics

“…In acoustic cavitation, the generated frequency components are mostly related to the driving frequency f 0 of the ultrasound transducer [3][4][5][6][7][8][9][10]. Researchers [11][12][13][14] have shown that with a so called self-sensing technique, that is using the ultrasound transducer simultaneously as both an actuator and a sensor, indicators for the presence of cavitation can be detected by observing the transducer's electrical signals. By now the transducer data [12,13] have been compared to those of microphones and hydrophones in order to reach a conclusion on the processes in the fluid.…”