Flow Of Spherical Particles Research Articles

Математическое моделирование потока капель распыливающего устройства

The paper presents the results of mathematical modeling, numerical and laboratory experiments aimed at developing an optical method for estimating the size distribution of droplets in a spray. The optical method is based on analyzing the brightness of light reflected by drops of a liquid. The ob-ject of study was a spray of a transparent liquid (distilled water) produced by a centrifugal axisym-metric nozzle. It is known that the intensity (brightness) of light reflected by a drop is proportional to the surface area of the drop, and for spherical drops, accordingly, to the square of the drop’s di-ameter (hereinafter, the terms intensity and brightness are used as synonyms). For a more detailed representation of the patterns of this dependence in the case of a flow of droplets, we considered a mathematical model representing the spray as a flow of spherical particles with parameterization of almost all significant properties: arbitrary distribution of droplets in size and speed as well as changes in these characteristics over time during the movement of drops along the flow. We ob-tained formulas and tested a mathematical model of nozzle spray that takes into account the change in droplet density due to the scattering of droplets in the spray cone and the inhomogeneity of veloc-ity fields. The zone of possible cessation of droplet fission was determined.

Discharge Flow of Spherical Particles from a Cylindrical Bin: Experiment and DEM Simulations

A series of the DEM simulations of the outflow of wooden spheres from a flat-bottomed container was reported, considering the maximum diameter to arrest the flow. Numerical simulations of the discharge process were performed, and the micro-mechanics of the discharged particles were described. The effect of the sliding friction coefficient between particles, rolling friction coefficient, and modulus of elasticity of particles on the clogging process was investigated. The results of the simulations of the mass flow rate of spheres have shown a fairly close agreement with the experimental results. The real particles of wood were not perfectly spherical, their properties were anisotropic, and their frictional properties were non-homogenously distributed on the surface. Nevertheless, these deviations from ideal conditions did not produce a considerable discrepancy in the results. No direct relationship between the interparticle friction and the clogging was found; however, a relationship between the stability of the dome formed at flow arrest and the rolling friction was observed. An increase in Young’s modulus of particles by two orders of magnitude did not affect the clogging process, but a slightly higher probability of clogging was found for softer particles.

DEM simulations of quasi-two-dimensional flow of spherical particles on a heap without sidewalls

Surface flows of granular materials find several important applications in both nature as well as industry. The effect of sidewalls on such flows is known to be large. Here, we study the rheology of such flows on a quasi two-dimensional heap without sidewalls, at different mass flow rates. It is seen that the surface angle of the heap, for all the mass flow rates, is the same and corresponds to the neutral angle. System variables such as the velocity, volume fraction and stresses are reported as a function of depth from the free surface of the heap. The friction coefficient and volume fraction are also studied as a function of the scaled local shear rate and these are also found to be independent of the mass flow rate. The behaviour observed in the present work is different from that reported in previous studies of surface flows with side walls.

Clogging of granular material in vertical pipes discharged at constant velocity

We report an experimental study on the flow of spherical particles through a vertical pipe discharged at constant velocity by means of a conveyor belt placed at the bottom. For a pipe diameter 3.67 times the diameter of the particles, we observe the development of hanging arches that stop the flow as they are able to support the weight of the particles above them. We find that the distribution of times that it takes until a stable clog develops, decays exponentially. This is compatible with a clogging probability that remains constant during the discharge. We also observe that the probability of clogging along the pipe decreases with the height, i.e. most of the clogs are developed near the bottom. This spatial dependence may be attributed to different pressure values within the pipe which might also be related to a spontaneous development of an helical structure of the grains inside the pipe.

A study of the mixing and segregation mechanisms in the Bohle Tote blender via DEM simulations

The flow of spherical particles in a tumbling blender is investigated using discrete element methods (DEM). Simulations are performed on a collection of particles that are mono-disperse and bi-disperse in size. The mono-disperse system is primarily used to assess the quality of mixing as a function of fill level and time. Results reveal that radial convection is faster than axial dispersion transport. This slow dispersive process hinders mixing performance in this geometry. We also find that both axial dispersion and radial convection worsen as the blender fill level is increased. This trend is corroborated by recent laboratory experiments performed in an identical geometry. Particle velocity profiles indicate that the flow is composed of two regions: i) a high velocity layer cascading atop ii) a nearly ‘solid body’ rotation region. Segregating mechanisms are investigated using bi-disperse systems, which show that small particles segregate in pockets at both extremes of the axis of rotation.