Theoretical Analysis Of Acoustic Cavitation In Supercritical Carbon Dioxide

Because of the special physical properties,supercritical fluid has been applied to many fields,such as active component extraction.However,the solubility of most materials in supercritical fluid is low,which leads to low work efficiency.Therefore,the enhancement technology of supercritical fluid begins to rise,and ultrasound enhancement has achieved remarkable results.Most researchers hold that the physical mechanism of ultrasonic enhanced supercritical fluid technology only involves mechanical effect,heating effect,activation effect and luminous effect,and whether cavitation effect plays an active force role is unclear.In this paper,the acoustic cavitation experiment of supercritical carbon dioxide that had been conducted by this research group will be introduced,and then the theory of supercritical carbon dioxide acoustic cavitation will be analyzed and discussed comprehensively.The contents are as follows:Based on the cavitation threshold of supercritical carbon dioxide,the equipment,procedures and results of the metal sheet corrosion test and the polymer production test conducted by this research group are introduced.The results show that cavitation can occur in supercritical carbon dioxide under the action of high-power ultrasonic wave.Modified LHSS equation and Tait equation are used as the basic equations to solve the state equation of supercritical carbon dioxide,the minimum mean error rate is used as the adaptability,the genetic algorithm is used to bring in the physical property data of the supercritical carbon dioxide,which is provided by the American National Standards Institute,and the two equation parameters are gotten based on the MATLAB platform,thus obtaining the new LHSS equation and isothermal Tait equation.Meanwhile,modified Tait equations at various temperatures are calculated,and the relationship between temperature and the equation parameters is established to get a new Tait equation based on PVT relationship.Through the cross check of the new LHSS equation and Tait equation,it is found that LHSS equation is applicable to the calculation of the physical property of supercritical fluid with large volume.The mean error rate of Tait equation is about 1%,which is very suitable for the calculation of the PVT properties of supercritical carbon dioxide.When a large amount of actual data is given,it is universal using genetic algorithm to solve the equation coefficients.In addition,based on the typical compressible cavitation bubble kinetic equation,by regarding the gas in the bubble as Van Der Waals Gas,in view of the derived supercritical carbon dioxide state equation,a kinetic model of Van Der Waals cavitation bubble in supercritical carbon dioxide is established.Using Runge-Kutta algorithm for solving,it is found that under the action of ultrasonic wave,Van Der Waals bubbles in supercritical carbon dioxide will also undergo an oscillating process until being stable.Finally,based on the natural resonance frequency formula of cavitation bubbles in liquid,in view of the supercritical carbon dioxide state equation,the natural resonance frequency formula of cavitation bubbles in supercritical carbon dioxide is derived,and the influence of resonance condition,sound pressure amplitude and fluid temperature on the phenomenon of acoustic cavitation in supercritical carbon dioxide is analyzed.The research results show that the natural resonance frequency in supercritical carbon dioxide is related to the initial radius of cavitation bubbles,the hydrostatic pressure and the temperature.In supercritical carbon dioxide,the estimation formulas of the natural resonance frequency and the initial radius of cavitation bubbles are in the same order of magnitude as the estimation formulas in water,and the influencing factors and influence extent of the cavitation effect are basically the same as those in water.These characteristics further indicate the possibility of cavitation in supercritical carbon dioxide in theory.