TURBULENT GAS-PARTICLE FLOW IN VERTICAL RISERS

Many experimental studies on the cross-sectional distribution of parti cles in vertical risers have revealed marked segregation of particles. These flows are inherently unsteady with large fluctuations in suspen sion density. In this article, we have analyzed the time-smoothed equa tions for the motion of dense suspensions to demonstrate the role of t hese fluctuations on the occurrence of segregation. It is shown that t he particles will congregate in regions where the kinetic energy of fl uctuations associated with the particles is small. In the context of t ransport of small particles such as FCC, a simplified model based on t he mixture velocity can be constructed. A speculative K-epsilon model based on this velocity is analyzed to illustrate the extent of segrega tion of particles afforded by unsteady fluctuations.