Granular flow fluid particle interactions

Before these individual canonical cases and several cases of misconceptions will be discussed in greater detail, it makes sense to first review the fundamental concept of fluid-particle interaction for both single-particle and multiple particle flows. Note that particle—particle interactions and particle collisions, the concepts of granular temperature and granular flow inclusively, are largely outside the scope of this chapter. 

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 ... 

We have examined the effect of kiln aerodynamics on fluid mixing and combustion. It is equally important to look at the aerodynamic effect on dust carryover from rotary kilns processing mineral materials. Although the principles behind particle motion are related to granular flow which will be covered in Chapter 4, the interaction of the flow of fluid in the freeboard and the active layer surface of the kiln bed is an aerodynamic phenomenon. 

In the first coarse-grained approach, the discrete phase is treated as an Eulerian continuum, interpenetrating with the real continuous phase. The particle-particle interactions are then captured by an effective particle phase rheology obtained from kinetic theory of granular flows. These so-called two-fluid (Euler-Euler) models have been very successful at predicting the dynamic properties of, e.g., gas-solid fluidized beds (see Van derHoefet al, 2008 Verma et al, 2013). Despite their success, two-fluid models also have their limitations they are usually limited to idealized cases ofmonodisperse hard sphere particles, while extensions to polydisperse mixtures (e.g., in size or in contact properties) are difficult to make. Also, because no particles are explicitly tracked, it is difficult to include particle properties which may vary from particle to particle, such as particle temperature, surface moisture concentration, or chemical surface species concentrations. 

In some cases the interaction between the particles and the surrounding fluid is of little significance, although at other times this can have a dominating effect on the behaviour of the system. Thus, in filtration or the flow of fluids through beds of granular particles, the characterisation of the porous mass as a whole is the principal feature, and the resistance to flow is dominated by the size and shape of the free space between the particles. In such situations, the particles are in physical contact with adjoining particles and there is... 

There are two main approaches for the numerical simulation of the gas-solid flow 1) Eulerian framework for the gas phase and Lagrangian framework for the dispersed phase (E-L) and 2) Eulerian framework for all phases (E-E). In the E-L approach, trajectories of dispersed phase particles are calculated by solving Newton s second law of motion for each dispersed particle, and the motion of the continuous phase (gas phase) is modeled using an Eulerian framework with the coupling of the particle-gas interaction force. This approach is also referred to as the distinct element method or discrete particle method when applied to a granular system. The fluid forces acting upon particles would include the drag force, lift force, virtual mass force, and Basset history force.Moreover, particle-wall and particle-particle collision models (such as hard sphere model, soft sphere model, or Monte Carlo techniques) are commonly employed for this approach. In the E-E approach, the particle cloud is treated as a continuum. Local mean... 

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