3 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.
4 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.
5 Coalescence efficiency
Collision part of the bubble or droplet coalescence occurs, and the definition of aggregate at the number of collisions and the ratio of the total number of collisions for the bubble or droplet coalescence efficiency. As the coalescence process is very complex, the existing models are mainly semi-theoretical semi-empirical model.According to coalescence theory, when the collision of two fluid particles, the contact of time (from two fluid particles from the beginning until the time of exposure) is greater than coalescence time (the film thinning began to drain liquid film rupture at any time or less thin to a critical thickness of the time), then the occurrence of coalescence of two fluid particles. Therefore, contact time and the accumulation of fluid particles and the ratio is a measure of the time whether the accumulation of fluid particles and the key parameters, the ratio is larger, the coalescence efficiency is close to 0, and this ratio is small, the coalescence efficiency approaches 1.
6 Conclusions and Outlook
Two-fluid particle coalescence and the process is usually that there are three steps: (1) two fluid particles near the contact, and hijacked a layer of liquid; (2) The further the two fluid particles close to, the hostage continuously drain liquid, thinning; (3) When a critical thickness of liquid film thinning to occur when the rupture occurred a coalescence. As the film rupture time is very short, usually assume that fluid particles near the contact and film thinning is the coalescence of the main stage, two stages of film thinning stage, especially as the focus of the study. Together and usually refers to the two fluid particles (bubbles or droplets) collide with each other and combined exposure process, rupture and coalescence is the opposite process. Fluid particle coalescence and rupture rate of only directly Jueding Fluid Particle size distribution and interfacial area, but also acts such as the interface is very important impact, affecting many industries DISSOCIATION AND RESPONSE equipment such as oil platforms evaporator, mixed Settler extraction tower, absorption tower, distillation tower, such as multiphase reactor performance and efficiency. Therefore, fluid particle coalescence and rupture rate of problems that have been widespread calls for an important issue.