Some problems of modeling the liquid cavitation degassing. I. Acoustic cavitation.

Abstract

In recent decades, cavitation methods of liquid degassing have become widely used, which today have practically replaced the traditional time-consuming mechanical and chemical methods of degassing in industry. The application of cavitation methods is based on the fact that a part of the neutral gases present in the liquid is not in a dissolved state, but in a so-called "free" state in the composition of a large number of vapor-gas bubbles, the size of which is measured on the scale of micro- and nanometers. The nature of the stable, long-term existence of such micro-bubbles has not yet found a reasonable explanation and is the subject of debate among researchers. Cavitation methods of degassing, both hydrodynamic and acoustic, are aimed precisely at the rapid removal of these bubbles from the liquid together with the free gas present in them. The advantage of using acoustic cavitation methods is the ability to precisely control the frequency and intensity of ultrasound, as well as the duration of sounding. Acoustic degassing methods are based on two mechanisms: the passage of dissolved gas inside pulsating bubbles due to the effect of "directed diffusion" and the convergence and subsequent coalescence of neighboring bubbles under the influence of force Bjerknes As a result, the growing bubbles quickly float up and leave the liquid together with the free gas. In recent years, a large number of articles on the comprehensive study of acoustic degassing processes have been published. According to the authors of these publications, the mechanism of degassing at the microscopic level and all the diversity of bubble dynamics, depending on the frequency and intensity of the sound, remain unclear. This article examines the main problems of modeling acoustic degassing processes, which confirm the absence of generally accepted clear ideas about the physical nature and mechanisms of cavitation phenomena and a general approach to the analysis of the obtained results. In order to develop research in this direction, the article also presents the results of a computational experiment on the coalescence of pulsating bubbles, conducted by the authors on the basis of a model of the dynamics of a single bubble previously created by them. As a result of the theoretical study, new, previously unknown information about the force interaction of pulsating bubbles of different sizes was obtained, which can be considered as a certain contribution to the understanding of the mechanisms of acoustic degassing.