Double-bubble ultrasonic cavitation dynamic differential equation obtained from superposition principle is normalized. MATLAB is used to analyse the effects of bubble linearity, double-bubble distance, sound frequency, sound pressure amplitude on cavitation process. Bifrequency ultrasound is introduced into the equation under discussion in this article. The calculation results show that bubble linearity is a main factor, which determines cavitation characteristics. The effect of sound pressure is strongest, and the frequency effect is the next strongest. Double bubble interactions affect cavitation characteristics to a certain extent, which reduces with distance increasing. Bifrequency ultrasound has a limited effect on cavitation characteristics, and it turns biggest when two component pressure amplitudes are equal.

Based on Jacobson's molecular free length theory in lipuids and the relationstip between the ultrasonic velocity and the molecular free length in organic liquids, the equation of pressure coefficient of ultrasonic velocity in organic liquid binary mixtures is derived. The calculated pressure coefficients of ultrasonic velocity are in good agreement with the measured results.

Molar sound velocity, molar adiabatic compressibility and Van der Waals constant of gaseons, liquid and supercritical carbon dioxide at different temperature and pressure are calculated using liquid acoustical models and data of sound velocity, density, molar volume and adiabatic compressibility of carbon dioxide provided by National Institute of Standards and Technology, USA. The results show that the liquid acoustical models can be used in study acoustical property of supercritical carbon dioxide in wide ranges of temperature and pressure. The surface tension, conglutination and diffusivity at different temperatures and pressures are calculated. And the mutative rules of these physical quantities are analyzed. The data can provide reference for supercritical liquid technique.

Based on the condensing vapor model, the expression of sound speed close to critical point is deduced,which shows the relationship between the sound speed and the density fluctuating index and thermal capacity at constant volume. Close to critical point, the sound speed of liquid carbon dioxide is inversely proportional to the density fluctuation index. The bigger the density fluctuation index, the smaller the sound speed. The sound speed is maximal at minimal density fluctuation index, where small fluctuations of density induces large fluctuations of sound speed. When the pressure increases and approaches to critical point, the rapid increase of thermal capacity induces decrease of sound speed. When the pressure increases and departs from critical point, the rapid decrease of thermal capacity at constant volume induces increase of sound speed. The calculated values of sound speed from the expression are in good agreement with the reference values from NIST.

碰撞因子， 碰撞因子温度系数， 克分子碰撞因子， 声速温度系数