Abstract: Firstly,according to the physical parameters of substance's critical point,the principles and methods for artificial implantation of cavitation nuclei in supercritical fluid are proposed.Secondly,by analyzing the physical characteristics of supercritical fluid,such as high hydrostatic pressure,low surface tension and no steam inside cavi- tation bubbles,the cavitation threshold of supercritical fluid is derived with the help of Rayleigh model.Then,by comprehensively taking into consideration the strong compressibility and physical characteristics of supercritical fluid,a simplified Gilmore equation for the calculation and analysis of supercritical fluid cavitation is given.More- over,according to the experimental data provided by the American National Standards Institute,density-pressure relationship and sound speed-pressure relationship of supercritical CO₂ fluid are fitted to solve the Gilmore equa- tion.Finally,the effects of initial radius,fluid temperature,sound pressure amplitude and ultrasonic frequency on the ultrasonic cavitation process are analyzed.The results indicate that the threshold of supercritical fluid is similar to hydrostatic pressure; and that,when ultrasonic sound pressure is greater than cavitation threshold,the movement of bubbles under the action of ultrasonic is similar to that of conventional liquids,such as water.

Key words: ultrasonic cavitation, cavitation bubble, cavitation threshold, sound pressure amplitude, supercritical fluid, Gilmore equation