Fluid motion in the presence of solid particles

The prime difficulty of modeling two-phase gas-solid flow is the interphase coupling, which deals with the effects of gas flow on the motion of solids and vice versa. Elgobashi (1991) proposed a classification for gas-solid suspensions based on the solid volume fraction es, which is shown in Fig. 2. When the solid volume fraction is very low, say es< 10-6, the presence of particles has a negligible effect on the gas flow, but their motion is influenced by the gas flow for sufficiently small inertia. This is called one-way coupling. In this case, the gas flow is treated as a pure fluid and the motion of particle phase is mainly controlled by the hydrodynamical forces (e.g., drag force, buoyancy force, and so... 

The effect of treating the particles as point particles (see also Balachandar, 2009) is that the detailed flow between the particles in response to the presence and motion of the particles remains unresolved (see, e.g., Derksen, 2003). As a result, a correlation is required in order to take the fluid—particle interaction into account. The Euler—Lagrange approach is most often used for simulating dilute gas—solid and liquid—sohd flows where the particle size is smaller than the smallest turbulent length scale (eddy) considered in the flow simulation of the carrier phase (Balachandar and Eaton, 2010). 

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