Increase In Fraction Of Particles Research Articles

Viscoelastic Fluid Flow Model for Hydrodynamic Behaviour of Magnetorheological Fluid in Valve and Shear Modes for a Damper System

In this present study, the flow behaviour of magnetorheological fluid in valve and shear modes for damping system is modelled and analysed. The fluid is modelled as viscoelastic fluid flowing between two parallel plates in pressure driven flow mode, and also as direct shear mode. In the work, the post-yield shear thinning or thickening behaviour of magnetorheological fluids are accounted for. The velocity and pressure distributions in the unsteady magnetorheological fluid flow between the electrodes of the damper are obtained by solving the momentum equation of the magnetorheological fluid flow using the Laplace transform method. There is an excellent agreement between the results of the present model and the results of the experimental studies. The adopted viscoelastic flow model describes that the rheological behaviour of the fluid is separated into distinct pre-yield and post-yield regimes. The fluid flow velocity, velocity gradient, and shear stresses have all been shown to be enhanced by an increase in the pressure drop. The viscosity of the fluid increases with an increase in the volume fraction of particles in the fluid, which causes the resistance of the fluid to flow to increase and thereby, reduces the fluid flow velocity. Fluid flow velocity is decreased as a result of increasing magnetic field strength. The design of clutches, rotary brakes, dampers, shock absorbers, prosthetic devices, polishing and grinding tools, etc. will all benefit greatly from the adoption of the current model.

MATHEMATICAL MODELING OF CELLULAR DETONATION WAVE SUPPRESSION BY SYSTEM OF INERT POROUS BODIES

Numerical simulation of the interaction of cellular detonation in a hydrogen-air mixture with a system of porous filters located at the walls of the channel was carried out. The main regimes and critical conditions for the attenuation and suppression of detonation in the filter system were obtained. In the first realized regime, at the volume fraction of filter particles less than critical, a detonation wave (DW) decelerates to a velocity less than the Chapman-Jouguet velocity and propagates in a stationary mode; a detonation cell size increases. In the second realized regime, at the volume fraction of filter particles equal or greater than critical, a DW splits into the shock wave (SW) and the lagging combustion front with the destruction of cellular structure. A map of detonation regimes was constructed. It follows from this map that with an increase in the volume fraction of particles in the filters, the gap between the filters can also be increased to successfully suppress the detonation.

Axisymmetric stagnation-point flow and heat transfer of nanofluid impinging on a cylinder with constant wall heat flux

The steady-state, viscous flow and heat transfer of nanofluid in the vicinity of an axisymmetric stagnation point of a stationary cylinder with constant wall heat flux is investigated. The impinging free-stream is steady and with a constant strain rate, k ?. Exact solution of the Navier-Stokes equations and energy equation are derived in this problem. A reduction of these equations is obtained by use of appropriate transformations introduced in this research. The general self-similar solution is obtained when the wall heat flux of the cylinder is constant. All the previous solutions are presented for Reynolds number Re = k ?a2/2n f ranging from 0.1 to 1000, selected values of heat flux and selected values of particle fractions where a is cylinder radius and n f is kinematic viscosity of the base fluid. For all Reynolds numbers, as the particle fraction increases, the depth of diffusion of the fluid velocity field in radial direction, the depth of the diffusion of the fluid velocity field in z-direction, shear-stresses and pressure function decreases. However, the depth of diffusion of the thermal boundary-layer increases. It is clear by adding nanoparticles to the base fluid there is a significant enhancement in Nusselt number and heat transfer.

3D Monte Carlo simulations on the aggregate structures of a suspension composed of cubic hematite particles

ABSTRACTIn the previous study, from the viewpoint of surface modification technology, we considered a quasi-2D suspension in thermodynamic equilibrium in order to investigate the characteristics of magnetic cubic particles on a material surface. The present study has been expanded to include 3D Monte Carlo simulations of a suspension of magnetic cubic particles in order to discuss a regime change in the structures of cubic particle aggregates. We attempt to elucidate the dependence of a regime change in the aggregate structures on a variety of factors. The main results obtained here are summarised as follows. If the magnetic interaction strength is sufficiently large, closely packed clusters are formed by repeat and expansion of a cluster unit composed of eight particles, which may be the most preferred configuration as it gives rise to a minimum energy. A regime change in the internal structure of aggregates appears in a narrow range with increasing magnetic interaction strength. As the applied magnetic field strength is increased, closely packed clusters collapse and are transformed into wall-like clusters that are formed along the magnetic field direction. An increase in the volumetric fraction of particles induces a regime change from thick chain-like clusters to the formation of wall-like clusters.

The influence of energy input on the particle size of disintegrated excess sludge in the ultrasonic disintegration process.

The objective of this research was to examine the influence of energy input on the particle size distribution of disintegrated sludge. The change of particle size distribution indicates the deagglomeration of flocs and disruption of micro-colonies. As the digestibility of sludge increases with dispersion, particle size analysis is an important factor in evaluating the disintegration process. Four different levels of energy input were used in the research: 10-100 kWh·m-3. All samples showed significant changes as far as dispersion (kdCST = 22.98-74.67, kdFCOD = 3.23-18.46), lysis (kdSCOD = 4.22-12.09), acidification (kdVFAs = 1.78-12.61), nitrogen release (kdTN = 4.02-21.61) indicators were concerned. Results indicate the gradual decrease of measured particle size with increasing energy input. The energy supplied to the disintegration process primarily promotes deagglomeration and with the rise of energy input, the destruction of cells. For EV = 50 and 100 kWh·m-3 an increased occurrence of lysis effects and increase in particle fraction <99.9 μm was noted. The highest efficiency evaluated by increase of filtered chemical oxygen demand (FCOD) and soluble COD (SCOD) per unit of volumetric energy - ΔCOD and ΔSCOD (mgO2·Wh-1) was obtained for Ev = 10 WhL-1, which corresponds to the most significant change in particle size distribution. The volume of particles <99.9 μm rose from 1.92% for non-disintegrated sludge to 26.62% for volumetric energy 100 kWh·m-3.

Experimental study of electrochemical mass transfer in an annular duct with the electrolyte nanofluid

The paper shows experimental studies on mass transfer phenomena in the nanofluid flowing through an annular channel. The effect of aluminium oxide nanoparticles on mass transfer was investigated in the channel with hydraulic diameter 10.5 mm.The experiment was performed using the electrochemical limiting current technique.A classical system for mass transfer measurements, based on ferricyanide ion reduction at the cathode and ferrocyanide ion oxidation at the anode has been applied. The base fluid (base-electrolyte) was composed of equimolar potassium ferri-ferrocyanide solution and sodium hydroxide solution. The nanofluid tested (nano-electrolyte) was composed of the base-electrolyte and spherical, 99.9% pure aluminium oxide nanoparticles, of about 40 nm in diameter. The nano-electrolyte used was characterized by volume particle fractions: 0.005%, 0.01%, 0.015%, 0.02%, 0.025%, 0.04%, 0.05% and 0.06%.Mass transfer processes during the forced transitional and turbulent flow of the nano-electrolyte through the horizontal annular channel were investigated. The fully developed hydrodynamic profile was considered. Mass transfer coefficients at the cathode attached to the inner surface of the channel were measured. The experiment was performed with the Reynolds numbers ranging from 2080 to 10430. Bulk ion concentrations in the electrolyte were measured experimentally during each test which minimized errors resulting from ion concentration decomposition. There occurred changes in the mass transfer coefficients depending both on nanoparticle concentration and the Reynolds number. With an increase in nanoparticle fraction, mass transfer was reduced. Measurements for the transitional and turbulent regime indicated that the mass transfer coefficients achieved their lowest values at the largest value of nanoparticle fraction. However, the reduction in mass transfer was not proportional to an increase in particle fraction. The maximum reduction of about 12% was observed for the largest Re numbers and the maximum particle fraction.

Experimental and Statistical Analysis of MgO Nanofluids for Thermal Enhancement in a Novel Flat Plate Heat Pipes

Metallic fluids like CuO, Al2O3, ZnO, SiO2 and TiO2 nanofluids were widely used for the development of working fluids in flat plate heat pipes except magnesium oxide (MgO). So, we initiate our idea to use MgO nanofluids in flat plate heat pipe as a working fluid material. MgO nanopowders were synthesized by wet chemical method. Solid state characterizations of synthesized nanopowders were carried out by Ultraviolet Spectroscopy (UV), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) techniques. Synthesized nanopowders were prepared as nanofluids by adding water and as well as water/ethylene glycol as a binary mixture. Thermal conductivity measurements of prepared nanofluids were studied using transient hot-wire apparatus. Response surface methodology based on the Box–Behnken design was implemented to investigate the influence of temperature (30–60[Formula: see text]C), particle fraction (1.5–4.5 vol.%), and solution pH (4–12) of nanofluids as the independent variables. A total of 17 experiments were accomplished for the construction of second-order polynomial equations for target output. All the influential factors, their mutual effects and their quadratic terms were statistically validated by analysis of variance (ANOVA). The optimum stability and thermal conductivity of MgO nanofluids with various temperature, volume fraction and solution pH were predicted and compared with experimental results. The results revealed that increase in particle fraction and pH of MgO nanofluids at certain points would increase thermal conductivity and become stable at nominal temperature.

A microstructure-based macro-micro multi-scale fine-blanking simulation of ferrite-cementite steels

The fine-blanking process of ferrite-cementite steels was simulated with a macro-micro multi-scale approach. In the macroscopic simulation, the effects of material and blanking clearance were investigated by evaluating the damage work density of the material in the center of the fine-blanking shearing zone. A series of microstructure-based models with different particle fraction and distribution were generated as sub-models for the microscopic simulations. Microscopic damage in the sub-models was predicted with the damage work model. The simulation results indicated that an increase in particle fraction and the existence of carbide banding accelerated the microscopic damage of the material in the shearing zone during fine-blanking. Micro cracks appeared and extended along the carbide band. In addition, an increase in blanking clearance speeded up the microscopic damage accumulation at the microscale and caused early fracture of the material in the shearing zone at the macro scale. The SEM observations of various fine-blanking specimens substantiated the predictions of the simulations and suggested that severe carbide banding would change the macro crack path in the sheets, adversely affecting the quality of the blanking surface.

Similarity Solution of Axisymmetric Stagnation-Point Flow and Heat Transfer of a Nanofluid on a Stationary Cylinder with Constant Wall Temperature

The steady state, viscous flow and heat transfer of a nanofluid in the vicinity of an axisymmetric stagnation point of a stationary cylinder is investigated. Exact solution of the Navier–Stokes equations and energy equation are derived in this problem. For all Reynolds numbers, as the particle fraction increases, the depth of diffusion of the thermal boundary layer and shear stresses decreases. It’s clear that by adding nanoparticles to the base fluid there is a significant enhancement in convective heat transfer coefficient and convective heat flux.

Streamrate stagnation-point flow of a nanofluid on a stationary cylinder

The steady-state, viscous flow of Nanofluid in the vicinity of an axisymmetric stagnation point of a stationary cylinder is investigated. The impinging free-stream is steady and with a constant strain rate . Exact solution of the Navier–Stokes equations is derived in this problem. A reduction of these equations is obtained by use of appropriate transformations introduced in this research. The general self-similar solution is obtained when the wall temperature of the cylinder is constant. All the solutions above are presented for Reynolds numbers ranging from 0.1 to 1000 and selected values of particle. For all Reynolds numbers, as the particle fraction increases, the depth of diffusion of the fluid velocity field in radial direction, the depth of the diffusion of the fluid velocity field in -direction, shear-stresses and pressure function decreases.

‏Ultrasonic Attenuation of (Al-SiC) Particulate Aluminum Matrix Composite

The present research deals with preparing (11) samples of composite materials with metal matrix represented by Aluminum alloy (AA3003)cast and particulate reinforced by (SiC) having particlesvolume fractions (5,10,15 Vol.%).The alloy matrix and composite materials were prepared by stir casting method. Stir casting technique wasused to increase the homogeneity distribution of the particles in alloy matrix. Average particlesizesof (75,106,150μm) were used. The aim of this study is to investigate the relationships between ultrasonic attenuation and stirrer speed ,reinforcement contents of SiC reinforced Al-alloy (AA3003)composites .Attenuation (longitudinal and shear)were measuredusing the pulse-echo amplitude technique with normal and angle probes of (45°,60°,and70°) and frequencies of (2 and 4MHz) .The results show an increase in volume fraction of particles causes an increase in attenuation. It was also found, that the ultrasonic attenuation decreases with increasing particle size. It was observed that an increases in stirrer speed, increases in the longitudinal ultrasonic attenuation.

High Temperature Oxidation of Nickel-based Cermet Coatings Composed of Al2O3 and TiO2 Nanosized Particles

AbstractNew technological challenges in oil production require materials that can resist high temperature oxidation. In-Situ Combustion (ISC) oil production technique is a new method that uses injection of air and ignition techniques to reduce the viscosity of bitumen in a reservoir and as a result crude bitumen can be produced and extracted from the reservoir. During the in-situ combustion process, production pipes and other mechanical components can be exposed to air-like gaseous environments at extreme temperatures as high as 700 °C. To protect or reduce the surface degradation of pipes and mechanical components used in in-situ combustion, the use of nickel-based ceramic-metallic (cermet) coating produced by co-electrodeposition of nanosized Al2O3 and TiO2 have been suggested and earlier research on these coatings have shown promising oxidation resistance against atmospheric oxygen and combustion gases at elevated temperatures. Co-electrodeposition of nickel-based cermet coatings is a low-cost method that has the benefit of allowing both internal and external surfaces of pipes and components to be coated during a single electroplating process. Research has shown that the volume fraction of dispersed nanosized Al2O3 and TiO2 particles in the nickel matrix which affects the oxidation resistance of the coating can be controlled by the concentration of these particles in the electrolyte solution, as well as the applied current density during electrodeposition. This paper investigates the high temperature oxidation behaviour of novel nanostructured cermet coatings composed of two types of dispersed nanosized ceramic particles (Al2O3 and TiO2) in a nickel matrix and produced by coelectrodeposition technique as a function of the concentration of these particles in the electrolyte solution and applied current density. For this purpose, high temperature oxidation tests were conducted in dry air for 96 hours at 700 °C to obtain mass changes (per unit of area) at specific time intervals. Statistical techniques as described in ASTM G16 were used to formulate the oxidation mass change as a function of time. The cross-section and surface of the oxidized coatings were examined for both visual and chemical analyses using wavelength dispersive x-ray spectroscopy (WDS) element mapping, X-ray Diffraction (XRD) and Energy-dispersive X-ray spectroscopy (EDS). The results showed that the volume fraction for each type of particle in the nickel matrix corresponded to its partial molar concentration in the electrolyte solutions. Increase in volume fraction of particles in the nickel matrix was correlated to lower oxidation rates. It was concluded that formation of Ni3TiO5 and NiTiO3 compounds can reduce the oxidation rate of cermet coatings by capturing some inward diffusing oxygen ions resulting in a lower number of nickel cations diffusing upward into the oxide layer.

Experimental study on the rheology of anisotropic, flocculated and low volume fraction colloids

In this work, we have investigated rheological behavior of colloids with a low particle volume fraction, and anisotropic and flocculated microstructures through measuring their viscosity and electrical resistance under varying shear rates together with utilizing several relevant characterization methods (i.e., Dynamic Light Scattering, Transmission Electron Microscopy, Atomic Force Microscopy, and Capacitance and Electrical resistance measurements). The colloids are formed through the suspension of hydrophilic/phobic fumed silica particle with attractive/repulsive interaction in polyethylene glycol and/or ethylene oxide-propylene oxide copolymer. It is observed that studied suspensions display shear thickening/thinning flow behavior depending on their microstructure (the spatial distribution and arrangements of particles in continuous media) and associated changes in cluster sizes, which are controlled by the break down of densified clusters (due to the shear induced mechanical and hydrodynamical forces) and the interaction forces among particleparticle and particles-polymers (owing to physicochemical effects). The detailed evaluation of the experimental results indicates that the shear thickening phenomena in low volume fraction, anisotropic and flocculated systems can be mainly attributed to the increase in the effective volume fraction of particles due to both hydrodynamic and physicochemical forces.

Activation and Fluoride-Assisted Phosphating of Aluminum-Silicon-Coated Steel

Phosphating is a crucial process in the corrosion protection of metals. Here, activation and fluoride-assisted tricationic phosphating is investigated on aluminum-silicon (AS) coated steel surfaces. Dynamic light scattering results from the activation bath show a bimodal size distribution, with hydrodynamic radii of ~400 nm and ~10 μm. For the smaller particle fraction, static light scattering results are consistent with the interpretation of disklike particles as scattering objects. Particles of the larger fraction sediment with time. In the presence of electrolyte, the scattering intensity from the larger particle fraction increases. Coagulation with time is suggested to be related to the decrease in activity of the activation bath. Scanning Auger microscopy (SAM) shows a higher phosphorus concentration after titanium phosphate activation in the Al-rich areas compared to the Si-rich areas of the AS coatings. There is no correlation between the size of the species in the activation bath, and the size of the phosphate-containing regions on the activated surface. Phosphating was performed in the presence of hexafluorosilicic acid, H2SiF6, ammonium hydrogen difluoride, NH4HF2, and both, at an initial pH of 2.5. The absence of crystals after phosphating with H2SiF6 is an indication that SiF6(2-) is the final product of the oxide dissolution in the presence of fluoride. In the presence of NH4HF2, the Si-rich regions of the surface are phosphated before the Si-poor (Al-rich) regions. Hence, the phosphate distribution after activation and after phosphating are opposite. These results show that a high surface concentration of phosphate after activation is not sufficient for a high coverage with phosphate crystals after phosphating.

Extended Release of Timolol from Nanoparticle-Loaded Fornix Insert for Glaucoma Therapy

We have developed a cylindrical insert that can be inserted in the fornix for extended release of glaucoma drug timolol. The insert is prepared by incorporating timolol-loaded nanoparticles into a poly hydroxyl ethyl methacrylate (p-HEMA) matrix. A 1-mm diameter, 7.5-mm long insert with 25% (w/w) particles can release timolol for about 10 days at an average rate of about 15 μg/day, which may be therapeutically effective. The increase in particle fraction increases drug loading, but also increases the release duration. The net effect of increasing the particle fraction is a significant increase in release duration, but a decrease in daily drug release rates, in the first few weeks. The release duration increases to about 1 and 3 months on increasing the particle fraction to 50% and 75%, respectively. The average daily release rates in the first 3 weeks are 15, 9, and 3 μg/day for the inserts with 50%, 75%, and 100% (w/w) particles, respectively. The mechanism of release is hydrolysis of the ester bond that links timolol to the propoxylated glyceryl triacrylate matrix, and thus the release profiles fit a first order reaction model. The water content of the inserts decreases from 31% to almost zero on increasing the particle loading from 25% to 100%. The rate constant for the hydrolysis decreases with an increase in particle loading in the insert most likely due to the reduction in the water content. The inserts can be packaged in wet conditions and stored in a refrigerator, but the inserts will exhibit a burst release caused by release of the drug from the particles into the p-HEMA matrix during the shelf life. Also, the magnitude of drug release after the initial burst is reduced due to the storage. The burst effect could potentially be avoided by packaging the inserts in a dry state, with hydration before insertion.

Effect of particle size distribution and calcium aluminate cement on the rheological behaviour of all-alumina refractory castables

Previous works based on statistical design of experiments (DoE) defined a model all-alumina self-flow refractory castable (SFRC) with optimized particle size distribution for simultaneous high flowability index (FI) and superior post-sintering performance.This work compares the SFRC rheological behaviour and setting time with those of alternative all-alumina castables with different Andreasen aggregate particle size distribution modulus, and of the equivalent castables containing calcium aluminate cement. The model castable showed Bingham behaviour with low yield stress, viscosity and thixotropy, guaranteeing easier casting and less wear in the casting and/or projection equipment. However, as the coarse particle fraction increases, the castable flow tends to be non-linear and changes from Bingham to Herschel–Bulkley. The cement containing castables quickly loose flowability despite the applied shear.This work confirmed previous conclusions based on FI measurements and demonstrates the adequacy of the use of FI values in the calculation of FI response surface by DoE.

Structural features of crystallization and hardening of amorphous alloy in the Fe-Cr-B system

The kinetics of crystallization and the influence that structural parameters of the liberated crystal phase have on the change in microhardness of Fe70Cr15B15 alloys were studied by transmission electron microscopy and X-ray structural analysis. It was established that the eutectic mechanism of crystallization is realized in the Fe70Cr15B15 alloy. The formed crystals with a eutectic phase represent barrel-like globules of iron boride Fe3B and α-FeCr alternating nanoplates in a ratio of 3: 1. It was found that the values of micro-hardness of the alloy rise linearly with an increase in the volume fraction of particles of the eutectic phase, resulting mainly from the difference between the moduli of elasticity of the amorphous matrix and the liberated eutectic-phase particles.

Mineral dissolution effects on mechanical strength

The fabric of soil media may change due to certain factors such as the dissolution of soluble mineral particles, desiccation, and cementation. The fabric changes lead to mechanical behaviour changes. The purpose of this study is to investigate the effects of mineral dissolution on mechanical strength. Experimental studies and numerical simulations are performed by using conventional direct shear and discrete element methods. The dissolution specimens are prepared with different volumetric soluble particle fractions in sandy soils. The dissolution of the specimens is implemented by saturating the salt–sand mixtures at the different confining stresses in the experimental study and reducing the sizes of soluble particles in the numerical simulations. Experimental results show that after the particle dissolution as the soluble particle fraction increases, the peak shear strength decreases, the void ratio increases, and the vertical displacement behaviour during shearing changes from dilative to contractive behaviour. The numerical simulations exhibit that the macro-behaviours match well with the experimental results. In addition, the micro-scale observation shows that the reduction in the shear strength of the soluble particle mixtures after the particle dissolution results from the reductions of the coordination number, the stability of the fabric, the ability to develop the anisotropy of the fabric, and the increases in the local voids and anisotropy. This study reveals that the particle dissolution has a significant effect on the shear strength, deformation, and fabric change.

Structure of aluminum alloys irradiated with reactor neutrons

Samples of the CAB-1 alloy in the initial state and irradiated with fast neutrons at an fluence of 2 × 1021 neutrons/cm2 have been studied by small-angle neutron scattering. It has been demonstrated that the observed large scattering cross sections are associated with the presence of nanosized pores with radii R ∼ 5–50 nm in the alloy, whereas for possible inclusions of the Mg2Si and Si phases, the contrast factors and limiting volume fractions lead to the estimated cross sections that are two orders of magnitude smaller than those observed in the experiment. As a result of the irradiation, the volume fraction of scattering objects (pores) 40–50 nm in radius decreases by a factor of more than two. This is compensated, to a large extent, by an increase in the total fraction of particles with radii of 5–8 and 20–25 nm as the total surface area of the scattering objects increases by 40%.

Magnetostrictive effect of magnetorheological elastomer

Magnetorheological elastomer (MRE) has been known for its magnetic field-dependent stiffness, but only a few works study its magnetostrictive property. The aim of this paper is to present results of studies on magnetostriction of the MRE consisting of carbonyl iron particles displaced in the matrix made of a silicone rubber. The MRE samples were placed in the magnetic field that varied from 0 to 636 kA/m, which was produced by the PEM-1022LS magnetic system. The longitudinal magnetostriction of the samples was measured by strain gauge. Three different tests were performed: (1) increased and decreased magnetic fields on four different volume fraction MREs with particles randomly dispersed, namely, 0%, 15%, 20% and 27%, (2) increased and decreased magnetic fields on three different MREs, with the same volume fraction of particles but varied orientation, namely, randomly, vertically and parallelly; (3) increased and decreased magnetic field three times continuously on the MRE with particles randomly oriented. Results indicated that (1) magnetostrictive effect increases with increase in volume fraction of particles and magnetostriction generally increases with increasing magnetic field, (2) orientation of particles influences the magnetostrictive performance significantly, (3) with increase of times of tests, saturation strain decayed and some remnant magnetostriction existed after switching off the magnetic field in each cycle. The mechanism of magnetostrictive effect of the composite was proposed to explain the phenomenon.