National University of Science and Technology “MISiS”, Moscow, Russia:

A. P. Tyukin, Applicant for a Doctoral Degree at the Department of Minerals and Man-Made Materials Concentration and Processing, Сandidate of Technical Sciences, e-mail: TukinAP@yandex.ru
T. I. Yushina, Head of the Department of Minerals and Man-Made Materials Concentration and Processing, Candidate of Technical Sciences

The application of waterless gravity concentration techniques is a lot more limited compared with that of conventional techniques that involve using aqueous medium. Correspondingly, the development, manufacturing and optimization of the equipment and techniques for gas-dynamic separation and classification of granular materials lack the intensity that applies to conventional aqueous circuits. At the same time, during density-based gas-dynamic separation of granular materials, the effective separation mass transfer can be reached when a stable dynamic pressure of the laminar gas flow on the particles in one direction is secured. It is extremely important to define a numerical criterion for gas-dynamic separation efficiency. Together with the difference in the speed of particles of the separated components, the speed ratio serves as a parameter that directly determines the gas-dynamic separation efficiency. With the separator parameters and regime being constant, the separation efficiency can be impacted by two factors:
– presence of particles of various diameters in the fed material of a particular size;
– a differing spherical shape factor of the particle.
This paper describes the results of a series of experiments that confirm the following conclusions:
1) maximum difference in the average speeds of particles of the separated components can be reached when the acceleration channel has a certain length and depends on the physical properties of the particles and the separation regime. It tends to increase as the linear gas speed rises. The limiting factor includes the need to ensure a laminar gas flow, which limits how much its linear speed can be increased;
2) the particle speed ratio is at its maximum when the acceleration has just begun and it then approaches 1 asymptotically. The limiting factor includes a mechanically unstable process of the mixture being fed in the acceleration channel, which does not allow to continuously shorten the acceleration path till the values approach 0.
A practical conclusion was made which says that a gas-dynamic separator should be designed to have an acceleration channel with minimum cross-sectional height and minimum length; and the maximum allowable speed of the working fluid should be specified to prevent its turbulent flow.

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