Peculiarities of solid particles separation in an unsteady turbulent flow of a pneumatic centrifugal classifier

Abstract

Abstract. The task of developing a centrifugal air classifier is to improve the efficiency of classification and to extend the range of regulation for separation boundaries of various micropowders, especially in the field of particle sizes equal to less than 10 microns.The mechanism of centrifugal separation of particles is considered in [1], where it is shown that motion of particles in a separation zone is both of a deterministic and random character. As currently it appears impossible to create an accurate model of the process taking into account the polydispersity of a powdered material, the concentration of a heterogeneous medium, the rotation of particles, as well as their interactions with each other and the channel walls, the turbulent fluctuations and the inverse effect of particles onto the carrier flow, it is advisable to consider the aerodynamics of the carrier flow and motions of individual particles in the carrier stream with a known velocity distribution separately [2].Let us consider the physical formulation of the problem for a profiled zone of a separation classifier (Fig. 1). The geometry of the separation classifier's zone, which actually is the zone in which the process of separating a powder into large and small products takes place, consists of two discs spaced H from each other, which rotate at a certain angular velocity d around the axis OZ.The bottom disc is flat, the upper one is profiled varying as Z = f (R). Along its perimeter the structure receives an outside air flow (cross section A-A) with a certain angular velocity g and a radial velocity component U 1 . Then, due to pressure difference, it passes through the working area of the structure and leaves it through the cross section C-C. Through the lower outlet (cross section R 2 -R 3 ) an additional gas flow Q add is supplied at an angular velocity add together with particles which, under the effect of the centrifugal and the aerodynamic forces, fall into coarse and fine fractions. Moreover, due to prevalence of the aerodynamic force, the fine separation product passes through the working area and it is removed from the separation element in the cross section C-C. Under the action of the centrifugal force the coarse fraction extraction is conducted through the cross section A-A.Formation of areas with a high concentration of particles not only degrades the aerodynamic situation in the separation zone, but also prevents the passage of fine particles into the fine separation product. Using unsteady oscillations of the carrier medium rate allows reduction of residence time for particles of a boundary size and a size close to it and, thereby, reduction of rope-formed compositions of particles in the separation zone of the centrifugal machine. a Corresponding author: zpavel@niipmm.tsu.ru This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.