on Aug 27, 2010
Multiphase flow system of gas - liquid or liquid - liquid was used experimental measurements and theoretical research in two ways. So far, the two-phase flow and mass transfer phase boundary area has a large number of topics. Basic theory of chemical engineering in recent years, further studies, the measurement of two-phase flow behavior of bubble motion and mass transfer of advanced methods are constantly emerging, the development of computer technology is changing, it all makes it possible to study chemical equipment from the micro occurred within process, so that people study and understand the dispersion process has entered a new phase.
Particles of crystalline and settlement process, microbial or cell growth, cloud and precipitation physics processes, including micro particles (such as droplets, particles, cells, etc.) group, study the dynamical behavior of particle swarm, on the understanding of these important physical processes .The particle system, while there is nucleation, growth, accumulation and micro-behavior, and the existence of particle size distribution. Micro-particle system behavior and particle size distribution of multi-phase system described in the two (multi) fluid model of turbulent closure, and white force is essential. To describe the microscopic behavior and particle size distribution, need to introduce population balance equation.
2 Role of single-bubble
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.
A .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.
B. 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.
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