L. Minkov

MEASUREMENT OF THE RATE OF SEDIMENTATION OF FINE PARTICLES IN A PLATELIKE CENTRIFUGE

The data of experimental investigation of the process of settling of fine particles in a platelike centrifuge have been given. The results obtained on sand and water have shown a nonmonotone character of the relative rate of sedimentation as a function of the total concentration of particles and the presence of the effect of a higher‐than‐average settling rate for the finest fractions. The methods of measurement of the sedimentation of fine particles are discussed, the experimental procedure is described, and systematic experimental errors are analyzed.

Controlling characteristics of hydrocyclone via additional water injection

The results of measuring the parameters of the classification of suspended solid particles by their sizes in a hydrocyclone equipped with a system for additional water injection are considered. The additional injection of water considerably changes the characteristics of the hydrocyclone. A mathematical model that predicts the trend in the change of hydrocyclone characteristics upon the injection of water is described. The mechanisms of the action of radial and tangential injection on classification have been explained. An efficient regime of injection is recommended to attain the required classification characteristics.

Modelling of change of the classifier separation characteristics by water injection into the apparatus

The investigation of the influence of additional water injection in a classifier on the particle separation process characteristics has been performed on the basis of numerical modelling. It has been shown that the increase in water injection velocity leads to the increase of both the cut size and the minimal value of separation curve. The change of the injector opening size influences only the minimum value of the separation function not altering the cut size at the specified water injection velocity.

Kinematics of flow of a slow suspended-particle flux about a sphere as applied to the sedimentation of a bidisperse suspension

A study is made of the kinematics of flow of fine particles about a coarse one in the process of sedimentation of the fine particles. An approximate analytical solution for the increase in the settling rate of fine particles, which is in good agreement with the approximation dependence obtained earlier as a result of numerical experiment, has been found. It has been shown that a relatively weak entrainment of most of the fine particles arriving at the peripheral region of the cell around the coarse particle is of primary importance for the effect of acceleration of sedimentation. A comparison with the available experimental data is made.

On the Accelerated Settling of Fine Particles in a Bidisperse Slurry

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.

Discharge characteristics of a hydrocyclone with built-in injector

On the basis of experimental research and numerical simulation, flow regularities in a 50-millimeter hydrocyclone with injector have been revealed. It is shown that the injected liquid comes out mostly through the lower outlet. At tangential injection toroidal vortex impeding main flow discharge through the lower outlet is formed.

Numerical Modelling of the Molten Metal Flow in a Disk Agitator Mixer

Numerical modelling of the molten metal flow in a crucible under the action of stirred disk agitator is carried out. The influence of the agitator rotational speed on the molten metal flow field is investigated. Dependences of the turbulent diffusivity and the power number on the agitator rotational speed are obtained. The effect of the interaction between the molten metal-air interface and agitator elements on the flow field in a crucible is shown.

Two Approaches for Simulating the Burning Surface in Gas Dynamics

Two approaches for simulating the burning surface in gas dynamics by means boundary conditions and right sides in the equations involving Dirac delta function are discussed. A comparison of numerical steady-state solutions and the exact ones in one-dimensional approximation is performed for two approaches. It is shown that the numerical solutions obtained with the finite-difference scheme of first order accuracy on the base of two considered approaches converge to each other when the mesh refinement is applied. The numerical solution for the steady state problem coincides with the analytical one, if the pressure at the boundary cell face is set equal to the pressure in the center of the boundary cell.

Propellant Grain with Maximum Combustion Efficiency of Metal

This paper reports on the ways of allocating the metal particles in the propellant grain of tube cross-sectional type to provide maximum combustion efficiency of metal. Two-dimensional flow field and the burning rate law govern a transport of the burning metal particles. The analytical correlation for the optimum allocation of metal particles in the case-bounded propellant grain of tube cross-sectional type under the assumption of equilibrium two-phase flow is deduced.

Optimum Disposition of Metal Particles in the Propellant Grain

Using the dispersed metal in solid propellants to increase the temperature of combustion products leads to such a problem as the specific impulse loss due to the incomplete combustion of metal particles in the exhaust products. A redistribution of metal loaded into the propellant grain is one of the methods to decrease the specific impulse loss. This paper reports on the ways to obtain the optimum metal particle disposition for the case-bounded propellant grain of tube cross-sectional type. Three different approaches to analyze the metal combustion efficiency are discussed. The influence of the dynamic nonequilibrium of two-phase flow on the optimum metal particles disposition in the propellant grain of tube cross-sectional type is investigated.