scholarly journals Fracture, aggregation and segregation in dry, granular flows

2021 ◽  
Vol 249 ◽  
pp. 03040
Author(s):  
James T. Jenkins ◽  
Michele Larcher
Keyword(s):  
Debris Flows ◽  
Relative Concentration ◽  
Granular Flows ◽  
Number Density ◽  
Small Particles ◽  
Particle Fracture ◽  
Large Particles ◽  
Pharmaceutical Production ◽  
Particle Kinetic Energy ◽  
Local Number

Particle fracture, the formation of small particles as the result of the breakage of large ones, and aggregation, the formation of large particles as the result of the combination of small ones, have important implications in industry (e.g. food processing, pharmaceutical production) and geophysics (e.g., snow avalanches and rock debris flows). Also, the presence of particles of different size that result from fracture and aggregation can induce segregation, resulting in the migration of large and small particles to different regions of the flow. Here, we formulate simple models for fracture and agglomeration and analyze the evolution of measures of the relative concentration of two sizes of spheres due the combined effects of fracture, aggregation, and segregation in dense, dry, granular flows. Particle breakage and combination is influenced by the frequency of collisions, by the local number density of the spheres, and by the particle kinetic energy. Segregation is predicted using a kinetic theory proposed by Larcher & Jenkins [2].

Structure of Microphase-Separated Silica/Siloxane Molecular Composites

1989 ◽  
Vol 171 ◽  
Author(s):  
Dale W. Schaefer ◽  
James E. Mark ◽  
David Mccarthy ◽  
Li Jian ◽  
C. -C. Sun ◽  
...  
Keyword(s):  
Phase Separation ◽  
Kinetic Studies ◽  
Organic Content ◽  
Small Particles ◽  
X Ray ◽  
Filled Elastomers ◽  
Polymeric Networks ◽  
Large Particles ◽  
Molecular Composites

ABSTRACTThe structure of several classes of silica/siloxane molecular composites is investigated using small-angle x-ray and neutron scattering. These filled elastomers can be prepared through different synthethic protocols leading to a range of fillers including particulates with both rough and smooth surfaces, particulates with dispersed interfaces, and polymeric networks. We also find examples of bicontinuous filler phases that we attribute to phase separation via spinodal decomposition. In-situ kinetic studies of particulate fillers show that the precipitate does not develop by conventional nucleation-and-growth. We see no evidence of growth by ripening whereby large particles grow by consumption of small particles. Rather, there appears to be a limiting size set by the elastomer network itself. Phase separation develops by continuous nucleation of particles and subsequent growth to the limiting size. We also briefly report studies of polymer-toughened glasses. In this case, we find no obvious correlation between organic content and structure.

Analysis of the Particles’ Movement Over the Flat and Profiled Rotating Discs surface in the Velocity Layer of the Viscous Gas

2021 ◽  
Vol 6 (2) ◽  
pp. 17-23
Author(s):  
Valeriy I. Pinakov ◽  
Konstantin V. Kulik ◽  
Boris E. Grinberg
Keyword(s):  
Qualitative Difference ◽  
Surface Region ◽  
Vertex Angle ◽  
Oscillation Regime ◽  
Small Particles ◽  
Magnus Force ◽  
Near Surface ◽  
Rotating Discs ◽  
Large Particles ◽  
Velocity Layer

Experiments on the rotating in the air cones with vertex angle β = 120º and flat disc shown that on frequencies Ω ≥ 2.5 hertz exists a qualitative difference in movement for the particles with diameters d ≈ 1 mm and d ≈ 0.1 mm. The particles with d ≈ 0.1 mm move in the near-surface region, the particles with d ≈ 1 mm jump up to 3 cm. Comparison of the spherical and aspheric (ellipsoid with axles d, d and 4 /3 d) particles' kinematics moving shown the inevitability of the large particles jump occurrence. Large particles come to self-oscillation regime by reason of periodically appearance of the Magnus force. Small particles are localized in the velocity layer

scholarly journals Gravitational differentiation in the regimes from stokes settling to Rayleigh–Raylor flows

2019 ◽  
pp. 15-30
Author(s):  
V. P. Trubitsyn
Keyword(s):  
Viscous Fluid ◽  
Interacting Particles ◽  
Small Particles ◽  
Continuous Transition ◽  
New Approach ◽  
Earth's Core ◽  
The Core ◽  
The Earth ◽  
Large Particles ◽  
Two Component

The Earth’s core was formed under gravitational differentiation in the course of the separation of iron and silicates. Most of the iron has gone into the core as early as when the Earth was growing. However, iron continued to precipitate even during the subsequent partial solidification which developed from the bottom upwards. At the different stages and in the different layers of the mantle, iron was deposited in different regimes. In this paper, the mechanisms of the deposition of a cloud of heavy interacting particles (or drops) in a viscous fluid are considered. A new approach suitable for analytical and numerical tracing the changes in the structure of the flows in a two-component suspension under continuous transition from the Stokessettling (for the case of a cloud of large particles) to the Rayleigh–Taylor flows and heavy diapirs (for the case of a cloud of small particles) is suggested. It is numerically and analytically shown that the both regimes are the different limiting cases of the sedimentation convection in suspensions.

scholarly journals Flow and fouling in a pleated membrane filter

2016 ◽  
Vol 795 ◽  
pp. 36-59 ◽  
Author(s):  
P. Sanaei ◽  
G. W. Richardson ◽  
T. Witelski ◽  
L. J. Cummings
Keyword(s):  
Membrane Fouling ◽  
Membrane Filter ◽  
Small Particles ◽  
Porous Support ◽  
Equal Area ◽  
Membrane Filters ◽  
Membrane Pores ◽  
Dead End ◽  
Large Particles ◽  
Membrane Geometry

Pleated membrane filters are widely used in many applications, and offer significantly better surface area to volume ratios than equal-area unpleated membrane filters. However, their filtration characteristics are markedly inferior to those of equivalent unpleated membrane filters in dead-end filtration. While several hypotheses have been advanced for this, one possibility is that the flow field induced by the pleating leads to spatially non-uniform fouling of the filter, which in turn degrades performance. In this paper we investigate this hypothesis by developing a simplified model for the flow and fouling within a pleated membrane filter. Our model accounts for the pleated membrane geometry (which affects the flow), for porous support layers surrounding the membrane, and for two membrane fouling mechanisms: (i) adsorption of very small particles within membrane pores; and (ii) blocking of entire pores by large particles. We use asymptotic techniques based on the small pleat aspect ratio to solve the model, and we compare solutions to those for the closest-equivalent unpleated filter.

scholarly journals Scattering Properties of Cometary Dust Based on Polarimetric Data

1991 ◽  
Vol 126 ◽  
pp. 249-252
Author(s):  
Sonoyo Mukai ◽  
Tadashi Mukai ◽  
Sen Kikuchi
Keyword(s):  
Linear Polarization ◽  
Phase Function ◽  
Mie Scattering ◽  
Mixing Ratio ◽  
Small Particles ◽  
Cometary Dust ◽  
Maximum Polarization ◽  
Large Particles ◽  
Lower Maximum ◽  
Phase Angles

AbstractReferring to the dust model in Mukai and Mukai(1990), where the scattering by large rough particles and Mie scattering by small particles are taken into account, a phase function of linear polarization of several comets is examined, especially in a region of phase angles α near a maximum polarization. A lower maximum polarization observed in comet Austin(1989c1) than those in comets West(1975n) and P/Halley leads a speculation that a mixing ratio of rough scattering to Mie scattering in comet Austin increases from a sun-comet distance r of 0.6 AU to 1.2 AU. This implies that a shortage of large particles in comet Austin occured in r <1 AU.

scholarly journals Are Large Particles of Iron Detrimental to Properties of Powder Metallurgy Steels?

Metals ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 431
Author(s):  
Ahmed Abdallah ◽  
Mahdi Habibnejad-Korayem ◽  
Dmitri V. Malakhov
Keyword(s):  
Powder Metallurgy ◽  
Apparent Density ◽  
Heavy Tail ◽  
Number Density ◽  
Iron Powders ◽  
Distribution Histogram ◽  
Compositional Uniformity ◽  
Large Particles ◽  
Size Distribution Histogram ◽  
Sintered Materials

It is experimentally shown that a removal of particles exceeding 100 microns in size from iron powders typically used in the fabrication of medium density powder metallurgy steels has a weak effect on apparent density, flowability and compressibility of blends as well as on density and strength of green bodies. An elimination of such particles, i.e., cutting off a heavy tail of a size distribution histogram at the 100 μm threshold, improves a compositional uniformity of sintered materials, but has no noticeable beneficial effect upon the strength of a final product, which is likely be determined by a fraction of pores and their shapes. A presence of soft pearlitic inclusions hardly matters unless their number density becomes so large that a 3D continuity (integrity) of a hard martensitic matrix is lost. This finding suggests that such an expensive preparatory step as sieving away large particles from as-received mixtures would bear no technological advantages. It was experimentally found that an attempt to lower the threshold below 100 μm noticeably worsened apparent density, flowability and compressibility.

Bacillus mycoides phages and their satellites

1984 ◽  
Vol 30 (5) ◽  
pp. 691-698 ◽  
Author(s):  
Anna S. Tikhonenko ◽  
Nina N. Belyaeva ◽  
Anna F. Kretova
Keyword(s):  
Inner Core ◽  
Structural Elements ◽  
Small Particles ◽  
Electron Microscopic ◽  
Bacillus Mycoides ◽  
Specific Antibodies ◽  
Helper Phage ◽  
Electron Microscopic Technique ◽  
Large Particles ◽  
The Relationship

The relationship between large and small particles of phages No. 1M and H17 reproducing simultaneously in one and the same bacterial cell of Bacillus mycoides was studied by the immune electron microscopic technique. The large particles of phages No. 1M and H17 were morphologically identical with phage No. 1 of B. mycoides, whereas only the tails of small particles of phages No. 1M and H17 were morphologically identical with the tail of phage No. 1. Antigens were identified in phages No. 1, No. 1M, and H17 using specific antibodies against phage No. 1, containing only large phage particles, and specific antibodies against phage H17 small heads. It was shown that (i) all structural elements of large particles and tails of small particles of phage No. 1M were antigenically identical with those of phage No. 1; (ii) all structural elements of small and large particles of phage H17, except the inner core of the tail, were antigenically different from phage No. 1; and (iii) the small heads of phages No. 1M and H17 were antigenically identical. Particles of phage No. 1 are morphologically and antigenically identical with the large particles of phage No. 1M and are antigenically different from the large particles of phage H17. Since the tails of small and large particles are antigenically identical in each phage pair (No. 1M and H17), this suggests that in both cases, the genome of a small defective phage codes for the synthesis of head proteins only, whereas its tail is borrowed from the corresponding helper phage. The small phage may therefore be considered as a satellite of the large phage which depends on a helper partner for production of complete particles and whose tail proteins are identical with those of the helper phage.

Assessment of Scavenge Efficiency for a Helicopter Particle Separation System

2011 ◽  
Author(s):  
Leiyong Jiang ◽  
Michael Benner ◽  
Jeff Bird
Keyword(s):  
Shape Factor ◽  
Flow Characteristics ◽  
Particle Separation ◽  
Operating Conditions ◽  
Separation Mechanism ◽  
Separation System ◽  
Small Particles ◽  
Inlet Velocity ◽  
Separation Systems ◽  
Large Particles

The effectiveness of a typical helicopter particle separation system has been numerically assessed at practical operating conditions and sand environments for various scenarios. The particle separation mechanism and its limitation are revealed by the flow characteristics and particle trajectories in the flow-field. The separation-by-inertia concept is effective for removing large particles, but problematic for small particles of diameter (d) ≤ 36μm. The particle size, shape factor, and rebound characteristics exert substantial effects on particle scavenge efficiency. On the other hand, the effects of gravity, particle inlet velocity, inlet mass distribution, and engine operating conditions on scavenge efficiency are minor or limited for the configurations and operating conditions considered in the present study. In addition, a few suggestions for further investigation on engine particle separation systems are included.

LDV measurements of an air-solid two-phase flow in a vertical pipe

1984 ◽  
Vol 139 ◽  
pp. 417-434 ◽  
Author(s):  
Yutaka Tsuji ◽  
Yoshinobu Morikawa ◽  
Hiroshi Shiomi
Keyword(s):  
Two Phase Flow ◽  
Laser Doppler Velocimeter ◽  
Medium Size ◽  
Phase Flow ◽  
Small Particles ◽  
Vertical Pipe ◽  
Two Phase ◽  
Air Turbulence ◽  
Large Particles ◽  
Particle Velocities

Measurements of air and solid-particle velocities were made in a vertical pipe two-phase flow by the use of a laser-Doppler velocimeter (LDV). Five kinds of plastic particles, diameters of which ranged from about 3 mm to 200 μm, were transported in a vertical pipe of 30 mm inner diameter. It was found that, the smaller the particle size, the flatter was the mean air velocity distribution for the same mass flow ratio of solids to air. Large particles increased air turbulence throughout the pipe section, while small particles reduced it. Both effects of promotion and suppression of turbulence were observed at the same time in the presence of particles of medium size, that is, the turbulence was increased around the pipe centre and reduced near the wall. The frequency spectrum of air turbulence normalized by the turbulence intensity was not changed by the large particles. In the presence of the small particles, the higher-frequency parts of the spectrum increased.

Particle Deposition in a Room-Scale Chamber With Particle Injection

2005 ◽  
Author(s):  
N. Zhang ◽  
Z. Charlie Zheng ◽  
L. Glasgow ◽  
B. Braley
Keyword(s):  
Particle Deposition ◽  
Particle Number ◽  
Particle Distribution ◽  
Turbulent Transport ◽  
Distribution Patterns ◽  
Particle Number Density ◽  
Number Density ◽  
Small Particles ◽  
Particle Injection ◽  
Simulation Results

A model simulating the deposition of small particles with turbulent transport, sedimentation, and coagulation, is presented. Experimental measurements were conducted in a room-scale chamber using a specially designed sequential sampler. The measured deposition-rate data are compared with the simulation results. Distributions of particle-number density at different times are plotted in several viewing planes to facilitate discussion of the particle distribution patterns.

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