Simple gas-liquid dispersion system is only a single continuous phase in the liquid bubbles, or gas continuous phase only a single droplet of the situation, which has done a lot of research. But the single bubble is too simplistic to distributed systems, obtained by the research findings can not be directly applied to real multi-bubble dispersed system. Currently, the most studied is generated from the single hole on the formation mechanism of single bubble motion characteristics, methods used and the potential flow model of the mechanical model.
Application of high-speed photography to observe the orifice in the stationary liquid Bubble formation process is generally believed that bubble formation of two phases: expansion stage and off stage. To determine the bubble diameter from the orifice Department can analyze the forces on the bubble is generally believed that the role of bubbles by four forces: buoyancy, surface forces, viscous forces and inertial force. If the gas flow is low, viscous forces and inertial forces can be ignored, just consider the role of buoyancy and surface forces. If the two forces balance, the system is stable, you can find the formula for calculating the bubble diameter. Many scholars at home and abroad for different types of continuous phase flow field, the force analysis of the bubble diameter varying formulas.
Potential flow model
(1) cross-flow of liquid is isothermal, non-sticky, non-uniform rotation and incompressible fluid;
(2) Gas is an ideal gas;
(3) Bubble cavity within the pressure and the pressure the same and always remains spherical, and only in his neck to maintain contact with the chamber, and downward movement in contact with the plate;
(4) A liquid gas liquid interfacial area was between the pressure and surface tension Cha result of the interaction but in the process of the formation to maintain constant surface tension.
The potential function of the knowledge to determine the unsteady Bernoulli equation of fluid sphere surface pressure distribution on this basis, the expansion of the sphere on the bubble, sliding and bubble surface pressure distribution and the process of bubble motion were study proposed to predict bubble size and deformation of the mathematical model, and proved to be the formation of gas bubbles in the fluid properties and fluid inertia force control, while the liquid inertia force can interface to the speed and acceleration, and gas-liquid quantitative calculation of the relative phase velocity.
The role of more than three bubbles
The industrial production in the actual order to speed up the mass transfer rate between the two phases would often they are decentralized This multi-bubble system, the dynamic characteristics of high-speed mechanical analysis is necessary to make it complex than the single bubble Much more complicated to find a suitable theory to explain the mechanism of the process of decentralization is very difficult. In the gas-liquid dispersion system Bubble kept campaigns and through deformation, rupture and coalescence and other changes .If so turbulent continuous phase fluid, acting on the dispersed particles to deform the surface of the force, including sticky Rapid oscillation of shear stress and dynamic pressure, dynamic pressure which turbulence plays a major role. As the turbulence High degree of randomness makes the flow of movement issues become very complex and distributed process of mechanism is also very sleepy Difficult. The current method has empirical distribution function method, stochastic process method, multiphase turbulent dynamics And Population Balance Model.
Bubble or droplet coalescence
Usually only consider the two bubble or droplet coalescence process. Together and usually that is divided into three steps. First, bubbles or droplets from a large distance and the collision near the beginning of the second stage is the film thinning, at this stage from the distance between bubbles or droplets smaller than the radius of liquid begins.At this stage, the bubble or droplet greatly reduced the relative velocity between the bubble and droplet flow rotating in the same time, the liquid film between two fluid particles thinning. The flow of fluid from an external force to persuade the two fluid particles along the direction of its center of mass close to, but because the restoring force caused by surface tension so close to the separation of two fluid particles. The third stage is a liquid film thinning to a certain extent, the distance between fluid particles as small as non-hydrodynamic gravitational instability leading to membrane rupture caused liquid to occur coalescence. As the third phase of the time compared with the previous two stages are very short, usually assume that fluid particle collision and coalescence film thinning is the main stage, two stages of film thinning stage, especially as the focus of the study.
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