Many experimental studies on the cross-sectional distribution of particles in vertical risers have revealed marked segregation of particles. These flows are inherently unsteady with large fluctuations in suspension density. In this article, we have analyzed the time-smoothed equations for the motion of dense suspensions to demonstrate the role of these fluctuations on the occurrence of segregation. It is shown that the particles will congregate in regions where the kinetic energy of fluctuations associated with the particles is small. In the context of transport of small particles such as FCC, a simplified model based on the mixture velocity can be constructed. A speculative K-e model based on this velocity is analyzed to illustrate the extent of segregation of particles afforded by unsteady fluctuations.
It is well-known that during high-velocity flow of
gas-particle mixtures through a vertical duct
the particles are distributed nonuniformly over the cross section.
We had shown in an earlier
paper that such a nonuniform state is sustained under fully-developed
flow conditions by the
large scale fluctuations accompanying such flows. In the present
study, we have carried out a
simple analysis of the developing flow problem to demonstrate that the
evolution of the
nonuniform distribution is indeed driven by turbophoresis.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.