Dynamic Simulation of Shear-induced Particle Migration in a Two-dimensional Circular Couette Device

The shear-induced migration of neutrally-buoyant non-colloidal circular particles in a two-dimensional circular Couette flow is investigated numerically with a distributed Lagrange multiplier based fictitious domain method.The effects of inertia and volume fraction on the particle migration are examined.The results indicate that inertia has a negative effect on the particle migration.In consistence with the experimental observations,the rapid migration of particles near the inner cylinder at the early stage is observed in the simulation,which is believed to be related to the chain-like clustering of particles.The migration of circular particles in a plane Poiseuille flow is also examined in order to further confirm the effect of such clustering on the particle migration at early stage.There is tendency for the particles in the vicinity of outer cylinder in the Couette device to pack into concentric rings at late stage in case of high particle concentration.

3D printed aluminum matrix composites with well-defined ordered structures of shear-induced aligned carbon fibers

Carbon fiber reinforced aluminum composites with ordered architectures of shear-induced aligned carbon fibers were fabricated by 3D printing.The microstructures of the printed and sintered samples and mechanical properties of the composites were investigated.Carbon fibers and aluminum powder were bonded together with resin.The spatial arrangement of the carbon fibers was fixed in the aluminum matrix by shear-induced alignment in the3D printing process.As a result,the elongation of the composites with a parallel arrangement of aligned fibers and the impact toughness of the composites with an orthogonal arrangement were 0.82%and 0.41 J/cm^(2),respectively,about 0.4 and 0.8 times higher than that of the random arrangement.

PARTICLE SIZE DISTRIBUTION IN A PLANAR JET FLOW UNDER-GOING SHEAR-INDUCED COAGULATION AND BREAKAGE

A CFD simulation is performed for a particle-laden planar jet flow.The Reynolds number is 8300,and the initial particle diameter is 1 μm.Large Eddy Simulation（LES） is employed to calculate the flow field,and the Taylor-series expansion moment method（TEMOM） is adopted to deal with the balance equation of particle coagulation and breakage.The shear-induced coagulation kernel,power-law breakage kernel and symmetric fragment distribution function are involved.The prediction of the distribution of the mean streamwise velocity of the jet is in good agreement with experimental data.The evolution of particle number concentration,volume concentration,polydispersity,particle diameter and standard geometric deviation is discussed in detail.The results show that as the jet travels downstream,the particle number concentration and volume concentration decrease,while their spans become wider.The polydispersity and particle diameter are very large in the shear layers at the upstream and in the core of vortex structures at the downstream.The particle standard geometric deviation changes within the range of 1.32 ≤σg≤ 1.96,and increases sharply in the shear layers.All variables approach the steady-state as time progresses.

Shear-induced particle segregation in binary mixtures:Verification of a percolation theory

Granular materials composed of different-sized grains may experience undesired segregation.Segregation is detrimental for a lot of industries because it leads to an increase in production costs and wastes.For these reasons,the segregation phenomena have been intensively studied in the last decades,and a lot of models have been provided by many researchers.However,these models are mainly based on empirical relations rather than physical considerations.This paper aims to confirm the main assumptions made by Volpato,Tirapelle,and Santomaso(2020)in their percolation theory by means of DEM simulations.The simulated geometry is a tilting shear box filled with few tracer particles in a bed of coarser sized grains,and simulations are performed for a range of tilting frequencies and size ratios.The results provide meaningful insight on the mathematical model parameters and allow us to say that the percolation theory relies on physically consistent assumptions.

Shear-induced Crystallization in Phase-separated Blends of Isotactic Polypropylene with Ethylene-Propylene-Diene Terpolymer

The compatibility between isotactic polypropylene（iPP） and ethylene-propylene-diene terpolymer（EPDM） in the blends was studied. SAXS analysis indicates that iPP and EPDM phases in the binary blend are incompatible. Isothermal crystallization behaviors of iPP in phase-separated iPP/EPDM were studied by in situ POM equipped with a Linkam shear hot stage. It was found that typical spherulites of iPP were formed both in neat iPP and in iPP/EPDM blends. The radial growth rate（d R/dt） of spherulites of iPP in the blend was not influenced by EPDM phases. Further investigations on isothermal crystallization of iPP in iPP/EPDM after shear with a fixed shear time showed that the crystallization rate of iPP in the blends increased with increasing shear rates, whereas, the crystallization rate was much lower than that of neat iPP. WAXD results showed that β-crystal iPP was formed in neat iPP as well as in iPP/EPDM blends after shearing and the percentage of β-crystal bore a relationship to the applied shear rate. The presence of EPDM resulted in lower percentage of β-crystal in the blends than that in neat iPP under the same constant shear conditions. SAXS experiments revealed that shear flow could induce formation of oriented lamellae in iPP and iPP in the blends, and the presence of EPDM led to a reduced fraction of oriented lamellae.

Removal of Co(Ⅱ) from aqueous solution by complexation-ultrafiltration and shear stability of PAA-Co complex

Removal of Co(Ⅱ) from aqueous solutions by complexation-ultrafiltration was investigated using polyacrylic acid sodium(PAAS) as complexing agent with the help of rotating disk membrane,and the shear ability of PAA-Co complex was studied. The effects of the mass ratio of PAAS to Co(Ⅱ)(P/M) and pH on the rejection of Co(Ⅱ) were studied,and the optimum conditions were P/M=8 and pH=7. The rejection of Co(Ⅱ) was over 97% when the rotating speed of the disk(n)was less than 710 r/min at the optimum P/M and pH. The distribution of the forms of cobalt on the membrane surface was established by the membrane partition model, and the critical shear rate,the smallest shear rate at which the PAA-Co complex begins to dissociate,was calculated to be1.4×10^4 s^-1,and the corresponding rotating speed was 710 r/min.The PAA-Co complex dissociated when the shear rate was greater than the critical one. The regeneration of PAAS and recovery of Co(Ⅱ) were achieved by shear-induced dissociation and ultrafiltration.

The antithrombotic activity of mini-type tomatoes is dependent on the particular variety and the stage of harvest. Lycopene content does not contribute to antithrombotic activity

The prevention of arterial thrombotic disease has a high priority in developed countries. We have focused our studies on the antithrombotic activity of those fruits and vegetables with the potential to prevent the disease, and the present study was undertaken as part of a series of investigations to examine beneficial fruits and vegetables. For this purpose, suitable laboratory tests as well as diets have been devised. In the current investigation, we have classified various tomato varieties with antithrombotic properties, and we now have extended our overall data to include more than ten antithrombotic varieties of fruits and vegetables. A method designed to measure shear-induced platelet activity (the Global Thrombosis Test, GTT) was used to assess haemostasis in vitro and a He-Ne laser-induced thrombosis technique was utilized to examine arterial thrombogenesis in vivo. Concentrations of the antioxidant, lycopene, were also measured. Three mini-type tomato varieties, coded “Cin”, “Pik” and “Caec”, and one mediumtype variety, coded “K”, were harvested at different stages of maturity. All mini-type varieties demonstrated antithrombotic activity at an early (green) stage. The antithrombotic activity decreased with the maturation of “Cin” and “Caec” but remained constant at all stages of maturity with “Pik”. The medium variety, “K”, did not possess antithrombotic activity. Lycopene was not detected at any stage in any of the tomato varieties, suggesting that this antioxidant did not contribute to antithrombotic activity. The present results indicated that the antithrombotic activity of tomatoes is dependent on the particular variety and stage of maturity, and that this activity is not due to lycopene.

Antithrombotic Effects of Different Strains of Lactic Acid Bacteria

Objective: The aim of the present study was to assess the antithrombotic properties of different strains of orally available antithrombotic lactic acid bacteria (LAB). Research Methods & Procedures: Antithrombotic activity, antiplatelet reactivity and/or thrombolytic activity, were measured in seven strains of LAB and LAB cell-free-extracts (LAB filtrates) using the shear-induced platelet reactivity/thrombolytic activity, The Global Thrombosis Test (GTT), with non-anticoagulated rat blood in vitro. Subsequently, the most potent antithrombotic strains identified in vitro were assessed in vivo after oral administration in mouse carotid arteries using a helium-neon laser-induced thrombosis model. Result: Five strains out of seven LAB (Lactobacillus paracasei KW 3100, Lactobacillus fermentum NBRC 3961, Lactobacillus pentosus JCM 8333, Leuconostoc oeni Elios 1, Pediococcus pentosaceus NK-2) promoted significant endogenous thrombolysis in vitro. In addition, one strain (Lactobacillus fermentum NBRC 3961) significantly inhibited shear-induced platelet re-activity. Three antithrombotic strains, Lactobacillus fermentum NBRC 3961, Leuconostoc oeni Elios 1, and Lactobacillus pentosus JCM 8333, were further assessed in vivo. The results demonstrated that filtrates, and the cells per se of these LAB, modulated antiplatelet activity and/or thrombolytic activity, and that the antithrombotic mechanisms were mainly influenced by protein content (60% - 70% of dry matter). Conclusion: The findings suggested that some strains of lactic acid bacteria could usefully provide the basis for the production of oral antithrombotic probiotics.

An Effective Approach for the Preparation of High Performance Thermal Conductive Polymer Composites Containing Liquid Metal

The preparation of high-performance thermal conductive composites containing liquid metals(LM)has attracted significant attention.However,the stable dispersion of LM within polymer solution and effective property contribution of liquid metals remains significant challenges that need to be overcome.Inspired by the properties of the dendritic structure of the tree root system in grasping the soil,“shear-induced precipitation-interfacial reset-reprotonation”processing strategy is proposed to prepare nanocomposites based on aramid micron fibers(AMFs)with hierarchical dendritic structure.Thanks to the combination of van der Waals force provided by hierarchical dendritic structure,electrostatic interaction between AMFs and LM,coordinative bonding of―NH to LM,together with interfacial re-setting and multi-step protonation,several features can be achieved through such strategy:conducive to the local filler network construction,improvement of interfacial interaction,improvement of the stability of filler dispersion in the solvent,and enhancement of mechanical and thermal properties of the films.The resulting AMFsp H=4/LM films demonstrate a thermal conductivity of 10.98 W·m^(-1)·K^(-1)at 70%filler content,improvement of 126.8%compared to ANFs/LM film;while maintaining a strength of~85.88 MPa,improvement of 77%compared to AMFs/LM film.They also possess insulation properties,enable heat dissipation for high power electronics.This work provides an effective strategy for the preparation of high performance polymer composites containing liquid metal.

An approach of the internal friction-dependent temperature changes for conventional and pure biogenic lubricating greases

This work investigated the temperature changes inside the bulk of lubricating greases under controlled high-shear stress conditions(250-500 s-1).For this purpose,a newly developed temperature-measuring cell called Calidus was successfully tested.The temperature changes(ΔT)have been related to the greases'components(thickener,base oil-type,and composition)and the structural degradation of the lubricating greases.Furthermore,a theoretical approach was proposed for calculating the internal temperature change of lubricating greases during shear stress.All greases showed an internal temperature profile characterised by a sudden rise inΔT within the first 4 h from starting the test and subsequentΔT decay until it reaches the steady state value.Furthermore,it was found that greases C1 and C5,formulated with lithium and calcium soap,respectively,with different soap content(16.1 wt%and 9.7 wt%,respectively),but the same base castor oil,showed the highest value of the maximumΔT,c.a.3.2 K,and the most drastic drop ofΔT.These greases showed both the highest specific densities and heat capacities.In addition,they showed the lowest ratio of expended energies(Rtee),which means more structural degradation in the stressed grease.On the contrary,the grease C3,with 13 wt%of Li-soap but the lowest base oil's viscosity,showed the lowest maximumΔT and the temperature profile was characterised by a moderate variation ofΔT along the test.The biogenic grease B3 developed a low-temperature change in the group of pure bio-genic greases close to grease C3.

Better Choice:Linear Long Chains Rather than Branched Ones to Improve Mechanical Performance of Polyethylene through Generating Shish-Kebabs

We utilized two structurally different long chains(linear and branched ultra-high molecular weight polyethylene)to reveal the dependence of flow-induced crystallization on long chain architecture,and prepared two bi-disperse systems of 98 wt%short chain and 2 wt%long chain.A flow field was applied to the bi-disperse polyethylene melt by a modified injection-molding machine,known as oscillation shear injection molding(OSIM).For the first time,the structural influence of long chains on flow-induced shish-kebab formation was systematically investigated.For the intermediate layer of OSIM samples,the branched long chains were better than the linear long chains at inducing shish-kebab formation,agreeing with the reported literatures,because the branches can maintain their oriented conformations longer.But unexpectedly,the reverse is the case for the core layer of OSIM samples,where the shear flow was much weaker than the intermediate layer.To understand the unexpected phenomenon,the lifetime of shishes induced by different long chains was compared.Result demonstrated that the linear-induced shishes possessed higher thermal stability than the branched-induced ones so that the linear-induced shishes could survive in the core layer of OSIM samples.Additionally,unlike other methods for flow-induced crystallization,OSIM could create samples for measuring mechanical properties,and thus offer the chance to reveal the relationship between structure and performance.The mechanical results demonstrated that both long chains remarkably enhanced the mechanical properties because of the significant promoting effect of long chains and intense flow fields on shish-kebab formation.However,the linear long chains induced more stable and flawless shishes with higher tensile strength and modulus(80.4 and 1613.5 Mpa,respectively)than the branched ones(74.4 and 1489.3 Mpa).Our research not only helps elucidate the mechanism of shish-kebab formation but also provides a better choice to reinforce polymers by adding long chains with suitable structure.