Disperse multiphase flow

Savage, S. B. (1983). Granular Flows at High Shear Rates. In Theory of Dispersed Multiphase Flow. Ed. R. E. Meyer. New York Academic Press. 

Fig. 7. Different situations that can be distinguished in modeling dispersed multiphase flow.

Figure 4.2 coupling between phases in dispersed multiphase flows (from Elghobashi, 1991). 

In most practical applications of dispersed multiphase flows, the suspension consists of non-spherical particles having different diameters. The range of particle diameters or particle size distribution may (non-reactive fluidization of particles) or... 

The recent progress in experimental techniques and applications of DNS and LES for turbulent multiphase flows may lead to new insights necessary to develop better computational models to simulate dispersed multiphase flows with wide particle size distribution in turbulent regimes. Until then, the simulations of such complex turbulent multiphase flow processes have to be accompanied by careful validation (to assess errors due to modeling) and error estimation (due to numerical issues) exercise. Applications of these models to simulate multiphase stirred reactors, bubble column reactors and fluidized bed reactors, are discussed in Part IV of this book. 

APPENDIX 4.1. TIME SCALES FOR DISPERSED MULTIPHASE FLOWS (FROM PEIRANO AND LECKNER, 1998)... 

With a Eulerian-Lagrangian approach, processes occurring at the particle surface can be modeled when simulating particle trajectories (for example, the process of dissolution or evaporation can be simulated). However, as the volume fraction of dispersed phase increases, the Eulerian-Lagrangian approach becomes increasingly computation intensive. A Eulerian-Eulerian approach more efficiently simulate such dispersed multiphase flows. 

The fluid dynamics of bubble column reactors is very complex and several different CFD models may have to be used to address critical reactor engineering issues. The application of various approaches to modeling dispersed multiphase flows, namely, Eulerian-Eulerian, Eulerian-Lagrangian and VOF approaches to simulate flow in a loop reactor, is discussed in Chapter 9 (Section 9.4). In this chapter, some examples of the application of these three approaches to simulating gas-liquid flow bubble columns are discussed. Before that, basic equations and boundary conditions used to simulate flow in bubble columns are briefly discussed. 

For dispersed multiphase flows a Lagrangian description of the dispersed phase are advantageous in many practical situations. In this concept the individual particles are treated as rigid spheres (i.e., neglecting particle deformation and internal flows) being so small that they can be considered as point centers of mass in space. The translational motion of the particle is governed by the Lagrangian form of Newton s second law [103, 148, 120, 38] ... 

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