Modeling the Vertical Transport of Dense Gas-Particle Suspensions
In the vertical transport of dense gas-solid flows, the tendency of particles to segregate toward the pipe wall has been well documented. Although earlier models based on the kinetic theory analogy have been able to predict such patterns for perfectly elastic particle-particle collisions, the predictive ability of these models breaks down for inelastic collisions. The mathematical model presented here incorporates two mechanisms that give rise to the lateral segregation of solids, namely the interactions associated with individual particles based on a kinetic theory treatment and the interactions associated with collections of particles based on an analogy with single-phase turbulent flows. In addition, the effect of the collective particle motion on the kinetic theory expressions, the description of which is crucial for the elimination of the undue sensitivity, is accounted for via a time-averaging procedure. The resulting model is able to predict many of the salient features associated with vertical gas-solid flows for realist values of the coefficient of restitution for particle-particle collisions. For example, model calculations display the segregation of particles at the pipe wall as well as the flooding phenomena. The effect of pipe diameter on the predicted relationship between operating variables is also examined; the results of which indicate a complex scale-up behavior. Finally, the quantitative ability of the model is also assessed based on comparisons with a wide range of available dense-phase experimental data.
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