Gas Dynamics of the Process of Separation of Granular Materials Into Fractions by Specific Weight
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Journal of Engineering Physics and Thermophysics, Vol. 93, No. 5, September, 2020
GAS DYNAMICS OF THE PROCESS OF SEPARATION OF GRANULAR MATERIALS INTO FRACTIONS BY SPECIFIC WEIGHT F. G. Akhmadiev
UDC 532.529:66.022.5
A mathematical model of the process of separation of granular materials by specific weight in fluidized beds has been constructed on the basis of the conservation equations of mass and momentum of the heterogeneous media mechanics. Computational and physical experiments on studying the separation process have been carried out. The regime and design parameters of the apparatus that ensure the needed degree of granular material separation into fractions have been determined. Keywords: mathematical model, gas dynamics, separation, specific weight, granular material, fluidized bed. Introduction. In technological processes the necessity often arises to separate granular materials by specific weight or to place separately various granular materials differing in specific weights. The processes of separation of granular materials have gained the greatest acceptance in agriculture in sorting out various granular cultures, in chemical technology, and in mining industry in the course of enrichment of ores. This process is especially difficult to realize when it is necessary to separate granular materials with close specific weights. Moreover, two problems are to be solved in this case: 1) separation of a granular material into fractions; 2) removal of separated fractions from the apparatus. The process of separation of granular materials by dimensions and the methods of their calculation have been studied fairly thoroughly, for example, they were considered in works [1, 2] that contain the review of the methods of mathematical simulation of these processes. For separating granular materials by specific weight apparatuses can be used in which separation is made in a thin fluidized bed, for example, apparatuses of the type described in [3]. During operation of such apparatuses, the original material with the differential distribution function W ( ρ20 ) arrives at the working separating unit that performs a reciprocating motion. In certain regimes of motion of the separating unit (deck) and of fluidization the granular material acquires a number of properties which are absent in an immovable charge and looks like a viscous fluid [4]. The granular material moves as a thin layer from the charging zone to the zone of takeoff of the heavy fraction between two guides. From below, the material layer is blown by a fluidized gas and is brought into a fluidized state. In this case, the gas velocity V1δcr is selected such that 0 0 the velocity of particles with density ρ2cr in the vertical direction could be V2 x1 (ρ2cr ) ≈ 0. Then the particles with density 0 0 0 0 ρ2 > ρ2cr descend to the base of the bed, while the light particles ρ2 < ρ2cr rise to the bed surface. Thus, as a result of their joint movement along the apparatus the separation of the light and heavy particles occurs, i.e., separation of the material into tw
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