Abstract
An estimation of increasing the volume average sedimentation velocity of fine particles in bidisperse suspension due to their capturing in the circulation zone formed in the laminar flow of incompressible viscous fluid around the spherical coarse particle is proposed. The estimation is important for an explanation of the nonmonotonic shape of the separation curve observed for hydrocyclones. The volume average sedimentation velocity is evaluated on the basis of a cellular model. The characteristic dimensions of the circulation zone are obtained on the basis of a numerical solution of Navier-Stokes equations. Furthermore, these calculations are used for modelling the fast sedimentation of fine particles during their cosedimentation in bidisperse suspension. It was found that the acceleration of sedimentation of fine particles is determined by the concentration of coarse particles in bidisperse suspension, and the sedimentation velocity of fine fraction is proportional to the square of the coarse and fine particle diameter ratio. The limitations of the proposed model are ascertained.
Highlights
In a number of industries machines based on the principle of settling of particles in a rotating fluid flow are used for the separation of particulate solids from air or liquid [1].Mathematical models for processes in such devices have long been developed that achieve impressive results
The aim of this paper is to study the circulation zone that occurs in the laminar flow of an incompressible viscous fluid around a spherical particle and the determination of the volume average sedimentation velocity of small particles during the sedimentation of bidisperse suspension, based on a cellular model
Based on a numerical simulation of the laminar flow of incompressible viscous fluid around a spherical particle the geometric characteristics of the circulation zone formed in the rear of the sphere depending on the Reynolds number for 25 < Re < 1000 were obtained
Summary
In a number of industries (mining, chemical, food, etc.) machines based on the principle of settling (sedimentation) of particles in a rotating fluid flow are used for the separation of particulate solids from air or liquid (air cyclones, hydrocyclones, centrifuges, decanters, etc.) [1].Mathematical models for processes in such devices have long been developed that achieve impressive results. In a number of industries (mining, chemical, food, etc.) machines based on the principle of settling (sedimentation) of particles in a rotating fluid flow are used for the separation of particulate solids from air or liquid (air cyclones, hydrocyclones, centrifuges, decanters, etc.) [1]. Reynolds stress model [2,3,4] and Large Eddy Simulation approach [5,6,7] are employed to describe the turbulent flow field in cyclones. A number of effects are in principle incapable of being clearly mathematically described Such effects include abnormal behavior of the so-called separation efficiency function, that is, the portion of the separated fraction of initial material depending on the particle size of the fraction
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