Instability analysis of vapour-filled bubbles in turbulent flows in ore flotation processes

Introduction. The subject of the study is a method of flotation, in accordance with which a mixture of air with hot (with saturation temperature > 104 °C) water vapour – vapour-air mixture is used as a gas phase in flotation. One of the consequences of aeration of cold slurry by air bubbles filled with hot water vapour is a change in their size distribution. Materials and methods. The study used a system in which water is separated from its vapour by a heat-insulating quasi-baffle as a thermophysical model of the process. The two-phase vapour-liquid flow starts at the moment when the quasi-baffle is instantly removed. The effectiveness of pulp aeration was experimentally tested on samples of copper-nickel ores from two deposits. Results. It is shown that the initial size distribution function is shifted towards smaller bubbles as a result of the turbulent velocity field. Discussion. Phase transitions cause changes in bubble size. As the vapour condenses, the bubble size decreases, but at the same time the heat exchange between the liquid medium and the vapour deteriorates, the pressure of which increases sharply as a result of overheating. As a result, the surface of the bubble makes periodic radial pulsations (oscillations). However, heat exchange between the phases is irreversible: the amount of heat received by the bubble during expansion due to evaporation of the carrier medium is less than it gives to the carrier medium in the form of condensation heat during compression. Therefore, the bubble size fluctuations are damped. But it is possible that the energy accumulated by the bubble during radial compression can be transferred into the energy of the pressure wave and the deformation oscillations caused by it, which are performed with a large amplitude and crush the bubble. Conclusion. The interaction of a vapour-air bubble with a liquid consists in phase transitions – condensation of vapour and evaporation of the carrier medium. The change of bubble size as a result of thermophysical transitions of vapour as a gas is of subordinate importance. Resume. High technological efficiency of the developed technology has been confirmed on samples of ores of the exploited deposits. The development of the theory of flotation by thermally loaded bubbles can go in the direction of research of physical and chemical regularities of the process.