Two-Phase Flow Models and Computational Fluid Dynamics

4 Two-Phase Flow Models and Computational Fluid Dynamics 

One-dimensional flow models are adopted in the early stages of model development for predicting the solids holdup and pressure drop in the riser. These models consider the steady flow of a uniform suspension. Four differential equations, including the gas continuity equation, solids phase continuity equation, gas-solid mixture momentum equation, and solids phase momentum equation, are used to describe the flow dynamics. The formulation of the solids phase momentum equation varies with the models employed [e.g., Arastoopour and Gidaspow, 1979 Gidaspow, 1994], The one-dimensional model does not simulate the prevailing characteristics of radial nonhomogeneity in the riser. Thus, two- or three-dimensional models are required. 

For the motion of a gas-solid suspension in the riser, both the gas and particle velocities have local averaged and random components. Thus, it is desirable to develop a mechanistic model which incorporates a variety of interactive effects due to both the gas and particle velocity components (see Chapter 5) as given in the following [Sinclair and Jackson, 1989]  

The two-fluid models considering these effects for the gas-solid flow in a riser can be described by Eqs. (5.168) through (5.170). In these models, the gas and solid are treated as two interpenetrating fluids (see 5.3). 

A0 Opening area for the mechanical valve or L-valve turbulent regime or choking to the fast fluidization regime 

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