Particle-fluid behavior

While Fig. 56 demonstrates, from modeling, the disparate nature between G/S and L/S fluidization, Fig. 57 shows continuity in particle-fluid behavior through properly selected intermediate systems, thus reconciling through theory the phenomenological discrimination between aggregative and particulate fluidization. 

So far, some researchers have analyzed particle fluidization behaviors in a RFB, however, they have not well studied yet, since particle fluidization behaviors are very complicated. In this study, fundamental particle fluidization behaviors of Geldart s group B particle in a RFB were numerically analyzed by using a Discrete Element Method (DEM)- Computational Fluid Dynamics (CFD) coupling model [3]. First of all, visualization of particle fluidization behaviors in a RFB was conducted. Relationship between bed pressure drop and gas velocity was also investigated by the numerical simulation. In addition, fluctuations of bed pressure drop and particle mixing behaviors of radial direction were numerically analyzed. 

There are several approaches to developing the correct scaling relationships. Probably the most straightforward is the nondimensional-ization of the governing equations. If we can write the proper equations governing the fluid and particle dynamic behavior, we can develop the proper scaling relationships even if we can t solve the equations (at present we can t). In essence, if a model is designed which follows the... 

Undoubtedly other factors may promote pseudoplastic behavior. For example, a decrease in size of swollen, solvated, or even entangled molecules or particles may occur under the influence of shearing stresses, to give the same changes in fluid behavior as in particle alignment. 

The efficiency of particle-fluid contacting in fluidization, popularly described in terms of the quality of fluidization, has its origin not only in the physical properties of the fluidizing medium and of the solid material of which the particles are composed, but also in the particle characteristics and in the group behavior of the particles while in motion. Particle characteristics include size, size distribution, shape, and surface roughness or texture, while... 

For granular flow (as distinct from the classical kinetic theory for a dilute gas) the net external force acting on the particle depends on the microscopic velocity because of the phase interaction terms introduced to consider the interstitial fluid behavior. However, the net force can be divided into two t3rpes of contributions, a set of external forces Fe which are independent of c and a separate steady drag force F i. Hence, the net force exerted on a particle is re-written as ... 

For the mechanical behavior of two particle-fluid systems to be simitar, it is necessary to have geometric, hydrodynamic, and particle trajectory similarity. Hydrodynamic similarity is achieved by fixing the Reynolds number for the flow around the collector. By (4.26), similarity of the particle trajectories depends on the Stokes number. Trajectory similarity also requires that the particle come within one radius of the surface at the same relative location. This means that the interception parameter, R = dp/L, must also be preserved. 

The heat transfer characteristics in multiphase systems depend strongly on the hydrodynamics, which vary significantly with particle properties. The particle size, size distribution, and shape affect the particle and fluid flow behavior through particle-fluid and particle-particle interactions. A discussion of the hydrodynamic characteristics of packed and fluidized beds follows. 

Two effects could, in principle, serve to invalidate this assumption. Highly unlikely in the troposphere is that sufficient heat would be generated by chemical reactions to influence the temperature. Absorption, reflection, and scattering of radiation by trace gases and particles could result in alterations of the fluid behavior. 

This equation describes the evolution of the distribution of the population of particles whose collective behavior reproduces fluid behavior. 

Visualization has played a central role in the development of the field of microfluidics and associated applications. It is both a natural desire and highly informative to see what is going on inside these small-scale systems. The inherent scale of these systems results in significant deviations from macroscale fluid behavior, most notably due to an increase in the role of surface effects and diffusive transport of mass, momentum, and energy. Unique micro- and nanoscale transport phenomena present many opportunities for advanced functionality as exploited by the many applications described in this encyclopedia and elsewhere. The scale of these systems, however, also presents some unique challenges with respect to visualization. Most notably, on the microscale the nonintrusive requirement precludes the use of many techniques commonly applied to macroscale flows, such as hot-wire anemometry and the injection of dye by mechanical means. In addition, it is not possible to observe the phenomena without the use of a microscope. Several visualization techniques have, however, been successfully applied to microscale flows. Like much of the research in microfluidics and nanofluidics, many proof-of-concept contributions have appeared in the 1990s, and subsequent advancement has been rapid. Most visualization techniques applied to microstructures may be conveniently divided into two categories particle-based methods and scalar-based methods [1]. 

In recent years, DEM has been used in combination with computational fluid dynamics (CFD) aiming at investigating particulate behavior in fluid phase. For a two-phase particle-fluid system, the solid motion and fluid mechanics are solved through the application of Newton s equations of motion for the discrete particles and Navier-Stokes equations for the continuum fluid [2]. 

Pneumatic conveying is a common method for transportation of particulate solids within or between processing plants. Particles are mobilized commonly using air and transported inside pipes or ducts. To attain a consistent flow of particles, particle mobilization and fluid pressure drop should be understood in detail. Stationary particles and excessive pressure drop could halt the flow. Figure 7.35 shows a study by Kuang et al. [84] on particle-gas behavior in a horizontal pipe with a view to investigate particle porosity and velocity distribution as well as gas pressure drop. 

Furthermore, NEMD enables the fluid microstructure to be studied in nonequilibrium steady states and to compare this structure with experiment (Hess Hanley 1982). The nonequilibrium distributions of particle positions and momenta are reflected in the thermophysical properties of viscosity, dilatancy and normal pressure differences. In molecular fluids such as lubricants, nonlinear fluid behavior is brought about in part by shear induced changes in molecular conformation. ... 

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