Increasing Particle Volume Fraction Research Articles

Experimental investigation on the thermal conductivity and shear viscosity of viscoelastic-fluid-based nanofluids

Viscoelastic-fluid-based nanofluids with dispersion of copper (Cu) nanoparticles in viscoelastic surfactant solution (aqueous solution of cetyltrimethylammonium chloride/sodium salicylate) were prepared. A comparative study of thermal conductivity and viscosity between viscoelastic-fluid-based Cu nanofluids and distilled water based nanofluids was then performed experimentally. Different concentrations of viscoelastic base fluid and volume fraction of Cu nanoparticles were matched in order to check their influences on fluid’s thermal conductivity and viscosity. The experimental results show that the viscoelastic-fluid-based Cu nanofluids have a higher thermal conductivity than viscoelastic base fluid, and its thermal conductivity increases with increasing temperature and increasing particle volume fraction. Furthermore, the viscoelastic-fluid-based Cu nanofluid shows a non-Newtonian behavior in its viscosity, and the viscosity increases with the increase of Cu nanoparticle concentration and decrease of temperature.

Influence of Nanoparticles in Lubricants on the Load Capacity of Hydrostatic Thrust Bearings

An analysis for the effect of nanoparticles in lubricants on load capacity is performed to study a rectangular thrust pad hydrostatic bearing with a central recess. The closed-form solution of the bearing load is derived analytically and presented for nanofluids with interparticle interaction. Results reveal that in the presence of nanoparticles, the enhanced viscosity could result in an increase in bearing load; moreover, this increase dramatically increases as particle volume fraction and/or interparticle interaction increases. The effect of nanoparticles on the bearing load can be magnified by decreasing the bearing gap.

Abrasive wear behaviour of B4C particle reinforced Al2024 MMCs

In this study, the effects of volume fraction and particle size of boron carbide on the abrasive wear properties of B4C particle reinforced aluminium alloy composites have been studied. For this purpose, a block-on-disc abrasion test apparatus was utilized where the samples slid against the abrasive suspension mixture at room conditions. The volume loss, specific wear rate and roughness of the samples have been evaluated. The effects of sliding time, particle content and particle size of B4C particles on the abrasive wear properties of the composites have been investigated. The dominant wear mechanisms were identified using scanning electron microscopy. The results showed that the specific wear rate of composites decreased with increasing particle volume fraction. Furthermore, the specific wear rate decreased with increasing the size of particle for the composites containing the same amount of B4C. Hence, it is deduced that aluminium alloy composites reinforced with larger B4C particles are more effective against the abrasive suspension mixture than those reinforced with smaller B4C particles.

Dynamics of solvent-free grafted nanoparticles

The diffusivity and structural relaxation characteristics of oligomer-grafted nanoparticles have been investigated with simulations of a previously proposed coarse-grained model at atmospheric pressure. Solvent-free, polymer-grafted nanoparticles as well as grafted nanoparticles in a melt were compared to a reference system of bare (ungrafted) particles in a melt. Whereas longer chains lead to a larger hydrodynamic radius and lower relative diffusivity for grafted particles in a melt, bulk solvent-free nanoparticles with longer chains have higher relative diffusivities than their short chain counterparts. Solvent-free nanoparticles with short chains undergo a glass transition as indicated by a vanishing diffusivity, diverging structural relaxation time and the formation of body-centered-cubic-like order. Nanoparticles with longer chains exhibit a more gradual increase in the structural relaxation time with decreasing temperature and concomitantly increasing particle volume fraction. The diffusivity of the long chain nanoparticles exhibits a minimum at an intermediate temperature and volume fraction where the polymer brushes of neighboring particles overlap, but must stretch to fill the interparticle space.

Numerical analysis of heat transfer enhancement with the use of γ-Al2O3/water nanofluid and longitudinal ribs in a curved duct

This paper presents a numerical investigation of heat transfer augmentation using internal longitudinal ribs and ?-Al2O3/ water nanofluid in a stationary curved square duct. The flow is assumed 3D, steady, laminar, and incompressible with constant properties. Computations have been done by solving Navier-Stokes and energy equations utilizing finite volume method. Water has been selected as the base fluid and thermo- physical properties of ?- Al2o3/ water nanofluid have been calculated using available correlations in the literature. The effects of Dean number, rib size and particle volume fraction on the heat transfer coefficient and pressure drop have been examined. Results show that nanoparticles can increase the heat transfer coefficient considerably. For any fixed Dean number, relative heat transfer rate (The ratio of the heat transfer coefficient in case the of ?- Al2o3/ water nanofluid to the base fluid) increases as the particle volume fraction increases; however, the addition of nanoparticle to the base fluid is more useful for low Dean numbers. In the case of water flow, results indicate that the ratio of heat transfer rate of ribbed duct to smooth duct is nearly independent of Dean number. Noticeable heat transfer enhancement, compared to water flow in smooth duct, can be achieved when ?-Al2O3/ water nanofluid is used as the working fluid in ribbed duct.

Predictive Model for Diffusion-Limited Aggregation Kinetics of Nanocolloids under High Concentration

Smoluchowski's equation for the rate of aggregation of colloidal particles under diffusion-limited conditions has set the basis for the interpretation of kinetics of aggregation phenomena. Nevertheless, its use is limited to sufficiently dilute conditions. In this work we propose a correction to Smoluchowski's equation by using a result derived by Richards ( J. Phys. Chem. 1986 , 85 , 3520 ) within the framework of trapping theory. This corrected aggregation kernel, which accounts for concentration dependence effects, has been implemented in a population-balance equations scheme and used to model the aggregation kinetics of colloidal particles undergoing diffusion-limited aggregation under concentrated conditions (up to a particle volume fraction of 30%). The predictions of population balance calculations have been validated by means of Brownian dynamic simulations. It was found that the corrected kernel can very well reproduce the results from Brownian dynamic simulations for all concentration values investigated, and is also able to accurately predict the time required by a suspension to reach the gel point. On the other hand, classical Smoluchowski's theory substantially underpredicts the rate of aggregation as well as the onset of gelation, with deviations becoming progressively more severe as the particle volume fraction increases.

Particle Effects on Penetration and Solidification of Flowing Mixed Melts on Metal Structures

In severe-accident analyses of liquid-metal-cooled reactors, assessing the relocation and solidification of disrupted core materials is of importance. We investigate here the fundamental characteristics of these behaviors in flowing melt mixed with solid particles under various conditions. To simulate the melts, we use a low-melting-point metal (viz., Bi-Sn-In alloy) mixed with various concentrations of copper and bronze as solid particles; the flow channels used were inclined open ones with a V-shaped cross section made of either stainless steel or brass plate. Transient melt flow was recorded, and melt penetration lengths and frozen melt distributions along the channel were measured. Results indicate that penetration length decreases for molten-metal/solid particle mixtures (mixed melts) compared with a pure molten metal (a pure melt), as well as decreases with decreasing solid particle size and increasing particle volume fraction in the melt. For the pure melt, we found only one freezing mode of all melt adhesions along the channel, whereas there were two freezing modes of melt separation with high solid particle concentrations, as well as melt adhesion, along the channel for mixed melts. The results obtained will be utilized in an experimental database to validate and improve physical models used for reactor safety analysis codes.

Mechanical behaviour of PVC/CaCO3Particulate Composites – Influence of Temperature

Abstract: This paper is concerned with the study of temperature influence on Young’s modulus, ultimate strength and fracture toughness properties of PVC/CaCO3particulate composites with different volume fractions. The tests were performed in three‐ and four‐point bending. The resonant technique was also used to analyse the influence of both volume fraction and temperature on Young’s modulus. Significant decrease of ultimate strength, fracture toughness and Young’s modulus was observed with the increase of the temperature. Ultimate strength decreases with the increase of particle volume fraction at room temperature. For the other temperatures, this decreasing trend is less clear. PVC/CaCO3flexural Young’s modulus calculated for a much lower loading segment increases with volume fraction. The same trend was obtained using the resonant technique. However, as the loading segment used to calculate the Young’s modulus was increased a significant decrease of Young’s modulus was obtained as a result of a progressive debonding at the particle‐matrix interface. A 2D simplified FE simulation also confirms such trend. The dependence of Young’s modulus relatively to the loading segment increases as the volume fraction is increased, leading to composite Young’s modulus below matrix value for higher volume fractions and higher loading segments. Fracture toughness decreases with volume fraction.

Analysis of losses in a double-negative metamaterial composed of magnetodielectric spheres embedded in a matrix

A simple-cubic lattice of identical, magnetodielectric spheres exhibiting double-negative (DNG) behavior is analyzed.An analytic expression for the threshold loss angle δth of the spheres, above which DNG behavior is extinguished, is derived by utilizing the Möbius transformation. The formula is valid for either dielectric or magnetic loss exhibited by the particles, and is derived based on the dipole approximation of Mie's theory of scattering by a sphere. For spheres with equal real relative permittivity and permeability, it is shown that δth increases as particle volume fraction increases. It is also shown that the loss angle of the effective medium can be controlled by appropriate choice of frequency. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26081

CFD studies on natural convection heat transfer of Al2O3-water nanofluids

This work is focused on numerical simulations of natural convection heat transfer in Al2O3-water nanofluids using computational fluid dynamics approach. Fluent v6.3 is used to simulate water based nanofluid considering it as a single phase. Thermo-physical properties of the nanofluids are considered in terms of volume fraction and size of nanoparticles, size of base fluid molecule and temperature. The numerical values of effective thermal conductivity have also been compared with the experimental values available in the literature. The numerical result simulated shows decrease in heat transfer with increase in particle volume fraction. Computed result shows similar trend in increase of Nusselt number with Relayigh number as depicted by experimental results. Streamlines and temperature profiles are plotted to demonstrate the effect.

Effect of suspended CuO nanoparticles on mass transfer to a rotating disc electrode

The effect of suspended CuO nanoparticles on the mass transfer to a rotating disc electrode was investigated experimentally, using the electrochemical limiting diffusion current technique. The particle volume fraction was from 0.39% to 1.94%. The rotating speed ranged from 100 to 1000 rpm, which yielded the Reynolds number between 10 and 110, based on the electrochemically active disc radius. The results showed that the addition of the suspended particles increased the limiting current and the plot of log I vs. log ω resulted in linear lines, of which slopes decreased with increasing particle volume fraction. The ratio of Sh/Sh o ranged from 1 to 1.5. The Sherwood number correlation as function of the Reynolds number and the particle volume fraction was also given.

Microstructure and abrasive wear behaviour of B4C particle reinforced 2014 Al matrix composites

In this study, the microstructure and abrasive wear properties of varying volume fraction of particles up to 12% B4C particle reinforced 2014 aluminium alloy metal matrix composites produced by stircasting method was investigated. The density, porosity and hardness of composites were also examined. Wear behaviour of B4C particle reinforced aluminium alloy composites was investigated by a block-on-disc abrasion test apparatus where the samples slid against the abrasive suspension mixture (contained 10 vol.% SiC particles and 90 vol.% oil) at room conditions. Wear tests performed under 92 N against the abrasive suspension mixture with a novel three body abrasive. For wear behaviour, the volume loss and specific rate of the samples have been measured and the effects of sliding time and the content of B4C particles on the abrasive wear properties of the composites have been evaluated. The dominant wear mechanisms were identified using SEM. Microscopic observation of the microstructures revealed that dispersion of B4C particles was generally uniform while increasing volume fraction led to agglomeration of the particles and porosity. The density of the composite decreased with increasing reinforcement volume fraction but the porosity and hardness increased with increasing particle content. Moreover, the specific wear rate of composite decreased with increasing particle volume fraction. The wear resistance of the composite was found to be considerably higher than that of the matrix alloy and increased with increasing particle content.

Effects of particle volume fraction on distortion of particle-arrayed structure during immobilization of colloidal crystals formed by poly(methyl methacrylate)-grafted silica in acetonitrile

Changes of particle array structure with particle volume fraction during immobilization of colloidal crystals, formed by poly(methyl methacrylate)-grafted silica in acetonitrile, were investigated. Immobilization of colloidal crystals formed in acetonitrile was carried out by two-step photo-radical copolymerization of methyl methacrylate and ethylene dimethacrylate to make organogel, followed by solidification after exchanging the solvent with methyl methacrylate. Crystallite size in colloidal crystals formed in acetonitrile was mostly unchanged with particle volume fraction in the range of 0.11–0.18, while the size and number of single crystals decreased during gelation. Disordering in particle array in immobilized colloidal crystals in gel and poly(methyl methacrylate) matrix was observed to decrease with increasing particle volume fraction less than 0.18 due to strong electrostatic repulsion between particles.

Fabrication of Tb 0.3Dy 0.7Fe 2/epoxy composites: Enhanced uniform magnetostrictive and mechanical properties using a dryprocess

To improve the uniformity of the magnetostrictive properties of Terfenol-D composites along the field direction, a dry method is developed in the present study. We examined the compaction pressure, particle volume fraction, particle size and composite configuration as factors that affected the magnetostrictive properties of the composites. The experimental results indicated that the magnetostrictive properties were improved with the increase of compaction pressure and particle volume fraction. In addition, larger average particle size was shown to result in more pronounced magnetostrictive properties. The particle alignment due to the orientation field is beneficial for the promotion of the magnetostrictive properties. The largest saturation magnetostriction and the maximum piezo-magnetic coefficient in the absence of a mechanical preload was obtained at 1005 ppm and 4.08 nm/A, respectively, for the aligned composite including a particle volume fraction of 77% and an average particle size of 210 μm.

Electroactive polydiphenylamine/poly(styrene-block-isoprene-block-styrene) (SIS) blends: Effects of particle concentration and electric field

Polymer blends between dedoped-polydiphenylamine (De_PDPA) and poly(strene-block-isoprene-block-styrene) triblock copolymer with 19%wt PS (D1114P, Kraton) were prepared to investigate electrorheological (ER) properties. Polydiphenylamine was synthesized by the interfacial oxidative polymerization and dedoped with ammonium hydroxide aqueous solution. ER properties were measured under an oscillatory shear mode in the frequency range of 0.1–100rad/s, at various electric field strengths between 0 and 2kV/mm. At 27°C and 1rad/s, the storage modulus sensitivities (ΔG'G'o) of the blends with 0, and 5%v/v are small, but dramatically increase at concentration above 5%v/v, consistent with the increase in the dielectric constant. The sensitivities are reduced when the particle volume fraction is above 20%v/v (2kV/mm) or 10%v/v (1kV/mm). The storage moduli (G′) of 20 and 30%v/v blends are nearly independent of temperature up to 370K but decrease beyond that. For the 0, 5, and 10%vv blends, the storage moduli increase with increasing temperature up to 370K and decrease at higher temperature. The softening of the blends at 370K coincides with the polystyrene glass transition temperature. At the lower concentrations, the blends still behave as elastomeric materials in which the elasticity is entropic in origin. In the deflection experiments, the deflection response increases with increasing particle volume fraction up to 10%v/v, and it decreases at higher concentration.

Field-induced columnar transition of biocompatible magnetic colloids: An aging study by magnetotransmissivity

The field dependence of the optical transmission of tartrate-coated and polyaspartate-coated magnetite-based aqueous colloids was studied. The colloidal stock samples were diluted to prepare a series of samples containing different particle volume fractions ranging from 0.17% up to 1.52% and measured at distinct times after preparation (1, 30, 120, 240, and 1460 days). We show that the magneto-transmissivity behavior is mainly described by the rotation of linear chains, at the low-field range, whereas the analysis of the data provided the measurement of the average chain length. Results also reveal that the optical transmissivity has a minimum at a particular critical field, whose origin is related to the onset of columns of chains built from isolated particle chains, i.e., due to a columnar phase transition. We found the critical field reducing as the particle volume fraction increases and as the sample's aging time increases. To investigate the origin of this phenomenon we used phase condensation models and Mie's theory applied to a chain of spheres and to an infinite cylinder. Possible implications for magnetophotonic colloidal-based devices and biomedical applications were discussed.

Discrete dislocation analysis of the mechanical response of silicon carbide reinforced aluminum nanocomposites

Metal matrix composites reinforced with ceramic particles exhibit improved thermo-mechanical properties compared to the host metal. In recent years, experiments have shown that reducing the size of the particles to the nanoscale dramatically increases the mechanical strength of these composites even at low particle volume fractions. However, numerical simulations using classical plasticity laws are unable to capture these trends correctly since these classical frameworks are length-scale independent. In this paper, the mechanical response of aluminum matrix reinforced with nanosized silicon carbide is analyzed using plane strain, discrete dislocation plasticity. In the simulations, plasticity arises from the collective motion of dislocations within an elastic medium. Constitutive rules are prescribed for nucleation, motion and annihilation of the dislocations. Calibration of various parameters or quantities which affect these processes is performed. The numerical results show improvements in the mechanical strength of the nanocomposite material with increasing particle volume fraction and decreasing particle size.

Formation of an fcc phase through a bcc metastable state in crystallization of charged colloidal particles

By in situ monitoring structural changes with the reflection spectrometer during the colloidal crystallization, we present direct experimental evidence of liquid-bcc-fcc phase transition in crystallization of charged colloidal particles, as a manifestation of the Ostwald's step rule. In addition, the lifetime of the bcc metastable structure in this system decreases significantly with increasing particle volume fraction, offering a possible explanation for "exceptions" to the step rule.

Optimal orientation field to manufacture magnetostrictive composites with high magnetostrictive performance

Magnetostrictive properties have relationship with the applied orientation field during the preparation of giant magnetostrictive composites. To understand the dependence of the optimal orientation field on particle volume fraction, composites with 20%, 30% and 50% particles by volume were fabricated by distributing Terfenol-D particles in an unsaturated polyester resin under various orientation fields. Their magnetostrictive properties were tested without pre-stress at room temperature. The results indicate that as the particle volume fraction increases, the optimal orientation field increases. The main reason for this phenomenon is the packing density for the composites with higher particle volume fraction is larger than that for those with lower particle content.

Role of the effective electrical conductivity of nanosuspensions in the generation of TiO 2 agglomerates with electrospray

Suspensions with varying volume fraction of TiO 2 nanoparticles and ionic strength were electrosprayed to obtain agglomerates of different characteristics, which were then deposited to produce films with tailored morphology, thickness, and porosity. The role of the nanoparticle volume fraction in both the effective electrical conductivity of TiO 2 nanosuspensions and the control of the size of agglomerates produced by electrospray was investigated. A simple modified equation for the effective electrical conductivity of TiO 2 nanoparticle suspensions was derived. The equation, which accounted for nanoparticles' diffuse ionic layer and their agglomeration in a liquid, showed that the effective electrical conductivity is not only a function of the liquid and particle conductivities, and the particle volume fraction but also a function of both the thickness of the adsorbed ionic layer on the particles and the particle size. Gradual increase of particle volume fraction resulted in an increase in the suspension's effective electrical conductivity, when the initial liquid conductivity was in the range of 10 −4–10 −3 S m −1. When the liquid conductivity was in the range of 10 −3–10 −2 S m −1; however, addition of particles did not have any significant effect on the effective electrical conductivity. Control over the size of the TiO 2 nanoparticle agglomerates was achieved by electrospraying suspensions with liquid electrical conductivity of the order of 10 −3 S m −1 and by varying the particle volume fraction. Electrospray deposition of suspensions with TiO 2 volume fraction=0.04% resulted in a more compact film with lower porosity and showed better water-splitting performance.