Nucleation stage of multicomponent bubbles of gases dissolved in a decompressed liquid

Abstract

A new kinetic analysis of degassing and swelling of a decompressed liquid solution with several dissolved gases has been presented. The analysis has been performed for the nucleation stage of formation and growth of supercritical gas bubbles in a closed system under conditions of a limited availability of the dissolved species. The nucleation stage is an important stage of degassing, on which a certain size distribution of gas bubbles is formed, being the starting point for further growth. This stage starts with the appearance of supercritical gas bubbles and is widely completed when the nucleation rate of supercritical gas bubbles diminishes by a decimal order. Neglecting the role of the Laplace pressure in large supercritical bubbles, we were able to introduce the concept of total gas supersaturation and to develop a theory of this stage for liquid solutions with arbitrary number and any values of supersaturations and solubilities of the dissolved gases. First, we have considered slowly growing bubbles within the mean-field approach assuming a stationary diffusion of gases to bubbles at moderate total gas supersaturation. In the case of large total gas supersaturation, we have built a description of fast growing bubbles on the basis of the extended excluded volume approach with nonstationary nonuniform diffusion shells around the bubbles and mean-field mixing of the concentration of gases at the external boundaries of the shells. A main novel feature of the developed theory is its ability to predict the kinetic behavior of the whole ensemble of bubbles with different sizes under changes in the initial gas composition in the liquid solution at its fast decompression. It has been shown that the effects of nonstationary diffusion may be very significant in the growth of multicomponent bubbles and, in particular, are responsible for a significant swelling of a decompressed liquid solution. Distribution of supercritical bubbles in sizes as a function of concentrations of solute gases at any moment of the nucleation stage, the duration of the nucleation stage, and the swelling ratio at the end of the nucleation stage have been determined.