Particle shape tunes fragility in hard polyhedron glass-formers

Soft Matter ◽  
2021 ◽  
Author(s):  
Erin G. Teich ◽  
Greg van Anders ◽  
Sharon C. Glotzer
Keyword(s):  
Relaxation Time ◽  
Particle Shape ◽  
Hard Particle ◽  
Density Dependent ◽  
Particle Shapes

More tetrahedral particle shapes make less fragile hard particle glass-formers, as evidenced by the density-dependent slope of the log of relaxation time, s(ϕ/ϕC) ≡ ∂ log τα/∂(ϕ/ϕC).

Evolvement law of a macroscopic traffic model accounting for density-dependent relaxation time

2017 ◽  
Vol 31 (31) ◽  
pp. 1750291 ◽  
Author(s):  
Yu-Qing Wang ◽  
Xing-Jian Chu ◽  
Chao-Fan Zhou ◽  
Bin Jia ◽  
Sen Lin ◽  
...  
Keyword(s):  
Relaxation Time ◽  
Traffic Flow ◽  
Flow Model ◽  
Initial Density ◽  
Traffic Model ◽  
Traffic Flow Model ◽  
Density Dependent ◽  
Macroscopic Traffic Flow ◽  
Boundary Perturbations ◽  
Initial Density Distribution

In this paper, a modified macroscopic traffic flow model is presented. The term of the density-dependent relaxation time is introduced here. The relation between the relaxation time and the density in traffic flow is presented quantitatively. Besides, a factor R depicting varied properties of traffic flow in different traffic states is also introduced in the formulation of the model. Furthermore, the evolvement law of traffic flow with distinctly initial density distribution and boundary perturbations is emphasized.

scholarly journals The effect of particle shape on the deformation and stress reduction of a gravel soil due to wetting

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Reza Mahinroosta ◽  
Vahid Oshtaghi
Keyword(s):  
Particle Size ◽  
Shear Stress ◽  
Particle Size Distribution ◽  
Normal Stress ◽  
Size Distribution ◽  
Stress Reduction ◽  
Particle Shape ◽  
Particle Breakage ◽  
Direct Shear ◽  
Particle Shapes

AbstractThis paper investigates the effect of particle shape on the stress reduction and collapse deformation of gravelly soil using a medium-scale direct shear test apparatus under different relative densities, normal stress, and shear stress levels. A new method based on the Micro-Deval test was introduced to produce sub-angular particles from angular particles. Therefore, two series of soil specimens were obtained with the same rock origin, particle size distribution, and relative density but different particle shapes. In addition to traditional direct shear tests on dry and wet specimens, a specific test procedure was applied to explore the stress reduction and collapse of soil specimens due to wetting. The results of the tests, including shear stress–shear displacement and vertical displacement-shear displacement, were compared. The results showed that the stress reduction and settlement due to wetting increased with vertical and shear stress levels in both types of particle shapes, with higher values in angular particle shapes. The particle breakage of the soil specimens was also studied quantitatively using the change in the particle size distribution before and after the test. It was shown that the wetting of the samples had more impact on the particle breakage in angular gravel than sub-angular gravel, which increased linearly with the normal stress.

scholarly journals Frac sand crushing characteristics and morphology changes under high compressive stress and implications for sand pack permeability

2016 ◽  
Vol 53 (9) ◽  
pp. 1412-1423 ◽  
Author(s):  
Wenbo Zheng ◽  
Dwayne Tannant
Keyword(s):  
Particle Shape ◽  
Void Ratio ◽  
Size Range ◽  
Particle Sizes ◽  
Shale Formations ◽  
Closure Stress ◽  
Compressive Stresses ◽  
Spherical Grains ◽  
Particle Shapes ◽  
Quartz Grains

Sand consisting of round quartz grains is widely used as a proppant during hydraulic fracturing to produce natural gas from tight shale formations. This paper presents results from sand characterization and crushing tests on Jordan Formation frac sand. It includes an assessment of grain-size reduction, changes in particle shape, and reduction in void ratio. It also examines the implications for permeability reduction through a sand pack caused by the closure stress on a hydraulic fracture. The sand from two size ranges (0.6 to 0.71 mm and 0.5 to 0.6 mm) was tested dry under applied compressive stresses of up to 40 MPa in a crushing cup. The overall sand pack stress–strain response becomes softer as grains are crushed. The particle shape shifts from nearly spherical grains to diametrically split grains and then to small elongated and angular fragments for the smaller particle sizes. The permeability of the sand pack reduces by more than 40% at a 20 MPa stress, which is mainly caused by a decrease in void ratio due to compaction. The permeability reduces by over 70% at a 40 MPa stress, which is primarily caused by void ratio decrease, reduction in particle size, and a shift away from spherical particle shapes. Compared to the ISO 13503-2 standard where only the sand crushing percentage after crushing tests is measured, this paper demonstrates that more information can be extracted from sand crushing tests and that sand pack permeability can be assessed to optimize frac sand selection. A sand with a larger size range has a higher crushing percentage, but is more permeable compared to a sand with a smaller size range. This further indicates that frac sand selection based only on sand crushing percentage is not sufficient to achieve better sand pack permeability.

scholarly journals Relevance of packing to colloidal self-assembly

2018 ◽  
Vol 115 (7) ◽  
pp. 1439-1444 ◽  
Author(s):  
Rose K. Cersonsky ◽  
Greg van Anders ◽  
Paul M. Dodd ◽  
Sharon C. Glotzer
Keyword(s):  
Crystal Structures ◽  
Self Assembly ◽  
Colloidal Crystals ◽  
Causal Mechanism ◽  
Hard Particle ◽  
Self Assembled ◽  
Particle Shapes ◽  
The Ideal

Since the 1920s, packing arguments have been used to rationalize crystal structures in systems ranging from atomic mixtures to colloidal crystals. Packing arguments have recently been applied to complex nanoparticle structures, where they often, but not always, work. We examine when, if ever, packing is a causal mechanism in hard particle approximations of colloidal crystals. We investigate three crystal structures composed of their ideal packing shapes. We show that, contrary to expectations, the ordering mechanism cannot be packing, even when the thermodynamically self-assembled structure is the same as that of the densest packing. We also show that the best particle shapes for hard particle colloidal crystals at any finite pressure are imperfect versions of the ideal packing shape.

Kinetic Simulations for Analysing the Wall Collision Process of Non-Spherical Particles

2002 ◽  
Author(s):  
M. Sommerfeld
Keyword(s):  
Particle Shape ◽  
Fluid Dynamic ◽  
Impact Angle ◽  
Distribution Functions ◽  
Spherical Particles ◽  
Collision Process ◽  
Wall Collision ◽  
Particle Velocities ◽  
The Impact ◽  
Particle Shapes

In wall-bounded gas-solid flows the wall collision process plays an important role and may be strongly affected by wall roughness and particle shape. The modelling of the particle-wall collision mostly relies on the assumption of spherical particles. To extend such models appropriately for non-spherical particles, two-dimensional kinetic simulations were performed for different particle shapes. This implies, that the particle translational and angular motion is calculated by considering the particle shape, however neglecting fluid dynamic effects. The change of the particle velocities during the impact and rebound process was calculated by solving the impulse equations together with Coulombs law of friction. The simulations were performed for a given initial particle velocity by varying impact angle and initial angular velocity. The results for 2000 particle wall collisions allowed us to derive the distribution functions of the impact parameters required to describe the wall collision process for non-spherical particles correctly. Moreover, other wall collision properties, such as rebound angle and velocity ratios could be determined. Finally also a comparison with measurements was possible.

scholarly journals Computational Investigation of Liquid Holdup and Wetting Efficiency Inside Trickle Bed Reactors with Different Catalyst Particle Shapes

2020 ◽  
Vol 10 (4) ◽  
pp. 1436
Author(s):  
Hao Deng ◽  
Baoqi Guo ◽  
He Dong ◽  
Cheng Liu ◽  
Zhongfeng Geng
Keyword(s):  
Fluid Flow ◽  
Particle Shape ◽  
Particle Surface ◽  
Liquid Density ◽  
Reactor Performance ◽  
Liquid Holdup ◽  
Trickle Bed Reactors ◽  
Vof Model ◽  
Trickle Bed ◽  
Particle Shapes

Liquid holdup and wetting efficiency are essential parameters for design of trickle bed reactors. Both parameters play an important role in reactor performance including pressure drop, conversion, and heat transfer. Empirical formulas are usually employed to calculate liquid holdup and wetting efficiency. However, factors such as particle shape and the wetting ability of liquid on the particle surface are not described clearly in traditional formulas. In this paper, actual random packing was built by DEM and CFD simulations were performed to investigate the factors affecting liquid holdup and wetting efficiency in trickle bed reactors, including particle shape, surface tension, contact angle, liquid viscosity, liquid density, liquid, and gas superficial velocity. Detailed fluid flow and liquid-solid interaction were described by VOF model. Four different particle shapes were investigated. It showed the particle shape has great effect and the 4-hole cylinder packing gained both highest liquid holdup and wetting efficiency. The overall simulations gave a detailed description of phase interactions and fluid flow in the voids between catalyst particles and these results could give further guidance for the design and operation of trickle bed reactors.

scholarly journals Effect of Particle Shape on Mechanical Behaviors of Rocks: A Numerical Study Using Clumped Particle Model

2013 ◽  
Vol 2013 ◽  
pp. 1-12 ◽  
Author(s):  
Guan Rong ◽  
Guang Liu ◽  
Di Hou ◽  
Chuang-bing Zhou
Keyword(s):  
Compression Test ◽  
Particle Shape ◽  
Triaxial Compression ◽  
Triaxial Compression Test ◽  
Particle Model ◽  
Model Parameters ◽  
Mechanical Behaviors ◽  
Rock Samples ◽  
Sphericity Index ◽  
Particle Shapes

Since rocks are aggregates of mineral particles, the effect of mineral microstructure on macroscopic mechanical behaviors of rocks is inneglectable. Rock samples of four different particle shapes are established in this study based on clumped particle model, and a sphericity index is used to quantify particle shape. Model parameters for simulation in PFC are obtained by triaxial compression test of quartz sandstone, and simulation of triaxial compression test is then conducted on four rock samples with different particle shapes. It is seen from the results that stress thresholds of rock samples such as crack initiation stress, crack damage stress, and peak stress decrease with the increasing of the sphericity index. The increase of sphericity leads to a drop of elastic modulus and a rise in Poisson ratio, while the decreasing sphericity usually results in the increase of cohesion and internal friction angle. Based on volume change of rock samples during simulation of triaxial compression test, variation of dilation angle with plastic strain is also studied.

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