Research On Characteristics Of Bubble Dynamics In Venturi

It generates high temperature and pressure when cavities collapse in the liquid in hydrodynamic cavitation, with a series of cavitational effects such as mechanical effect, thermal effect, chemical effect and optical effect. Hydrodynamic cavitation can be used as a source of energy input to enhance special physical and chemical processes. It possesses of the advantage of low energy consumption, high efficiency, and less pollution, which has broad economic and social benefits.This dissertation is aimed at finding out the mechanism of hydrodynamic cavitational enhancement and the evolution of bubble dynamics. Then the relationship between enhancement effect and influcing factors can be built to guide the designing and optimization of hydrodynamic cavitational reactor. Researches are mainly developed into such directions as follow.The comparisons between the three goveming equations (Rayleigh equation, Rayleigh-Plesset equation, Gilmore equation) are done based on the bubble dynamics, both in theory and in experiment. The Gilmore equation gives more realistic picture of single bubble dynamics, which is choosen to simulate the bubble evolution and collapse intensity in venturi tube. The effect of liquid viscosity, surface tension and compressibility on bubble behavior is studied. The influence of operating parameters, geometric parameters, and character of flow filed in the collapse intensity is investigated. A correlation is developed to predict the collapse pressure generated as a function of the influencing factors.A numerical method is developed to solve the collapse pressure of bubble cluster, which is origin of the energy transfer theory from the collapsing bubbles to the nearby-uncollapsed bubbles. The Monte Carlo method is used to deal with the bubble cluster model considering the size distribution of bubbles. The statistical property and collapse pressure in collapse process are obtained by combining the bubble governing equation, the model of bubble collapsing by the layer, and the pressure field of cavitating flow. The effect of operating parameters and geometric parameters is analyzed. It is also developed a correlation between collapse pressure and influencing factors. The numerical results show good accordance with experimental results.The collapse profiles of bubble cluster are described numerically on the bases of collapse model and the model of cavitating flow. It shows the evolution process of bubble cluster from graphic structure. The cavitation area and intensity can be predicted from the results. The numerical results of collapse profiles agree well with the experimental pictures.Based on the theory of Computational Fluid Dynamic, the simulation of the cavitating flow in venturi is carried out by using CFD software Fluent, with a User-Defined Function for RNG k-εturbulence model. On the bases of these, the effect of modified turbulent viscosity on simulation results is discussed, and the cycle process of unsteady cavitating flow is described, and the reason of bubble cluster shedding is analyzed. Finally, the analysis of operating parameters and geometric parameters affecting the characteristics of cavitating flow is done.