High Solid Volume Fraction Research Articles

Flow Behavior of Native Corn and Potato Starch Granules in Aqueous Suspensions

The flow behavior of native corn and potato starch granule suspensions prepared in a concentrated sucrose solution has been investigated. Measurements were performed using a rotational rheometer with a concentric cylinder geometry. Starch suspensions were dilute to semi-concentrated (1 % to 25 % by volume). Shear and dynamic viscosity were measured by shear flow and dynamic oscillatory testing at 20, 50 and 80 °C. The starch suspensions exhibited essentially Newtonian behavior at all solid contents, although at higher solid volume fractions there was evidence of slight shear thickening. The relative viscosity of suspensions increased with increasing starch granule content, and the data conformed well to Maron-Pierce’s equation. An increase in maximum packing fraction and gravitational depletion of the starch granules with increasing temperature resulted in lower relative viscosities at higher temperatures. Also, the relative viscosities of potato starch granule suspensions with bigger, more oval and anisometric particles were lower than those of corn starch suspensions where granules were closer to sphericity but were angular in shape. Oscillatory shear testing results showed the presence of viscoelastic properties at intermediate solid volume fractions at low frequencies; in addition, the relative shear viscosity was higher than the relative dynamic viscosity, probably due to the formation of shear-induced structures during the shear flow test.

Feed rate effect on particulate acceleration in Cold Spray under low stagnation pressure conditions

Abstract Cold Spray (CS) is an emerging coating process, which is attracting the interest of research and industry due to its rapid solid-state particle deposition mechanism and the advantages over conventional high temperature spray technologies. The acceleration of solid particles by means of a gas flow expanding to supersonic regimes is critical to process efficiency; previous studies rarely address the particle feed rate as an influential parameter for the acceleration. Higher particle feed rates typically result in high solid volume fractions in critical areas of the supersonic nozzle, such as at the throat cross-section. In this study, Particle Image Velocimetry (PIV) was employed to study the feed-rate relationship with particle velocity in CS at low stagnation pressure conditions. The experimental observations were compared against a 2D–axisymmetric Eulerian–Lagrangian model using ANSYS-Fluent v14.5. It was experimentally found that the mean particle velocity in the jet decreases with increasing particulate loading. Moreover, the particle velocity distribution depends on the particle material and shape. It was therefore possible to evaluate the effect of particle loading on exit-nozzle particle speed, and simulate this using Computational Fluid Dynamics (CFD).

An experimental study on thermal conductivity of F-MWCNTs–Fe3O4/EG hybrid nanofluid: Effects of temperature and concentration

In this paper, an experimental study on the effects of temperature and concentration on the thermal conductivity of f-MWCNTs–Fe3O4/EG hybrid nanofluid is presented. The experiments were carried out for solid volume fraction range of 0 to 2.3% in temperatures ranging from 25°C to 50°C. The results revealed that the thermal conductivity ratio enhances with increasing the solid volume fraction and temperature. Results also showed that, at higher temperatures, the variation of thermal conductivity ratio with solid volume fraction was more than that at lower temperatures. Moreover, the effect of temperature on the thermal conductivity ratio was more noticeable at higher solid volume fractions. The thermal conductivity measurements also showed that the maximum thermal conductivity ratio was 30%, which occurred at temperature of 50°C for solid volume fraction of 2.3%. Finally, for engineering applications, based on experimental results, a precise correlation was suggested to predict the thermal conductivity of f-MWCNTs–Fe3O4/EG hybrid nanofluids.

Measurement of thermal conductivity of ZnO–TiO2/EG hybrid nanofluid

The hybrid nanofluids are novel nanofluids and can be prepared by suspending various kinds of nanoparticles in base fluid. In this paper, an experimental investigation on the effects of temperature and nanoparticles concentration on the thermal conductivity of ZnO–TiO2/EG hybrid nanofluids is presented. The experiments were implemented at temperature ranging from 25 to 50 °C and solid volume fraction range of 0–3.5 %. Experiments indicate that the thermal conductivity enhances with increasing the solid volume fraction and temperature. It was found that the variation of thermal conductivity enhancement of nanofluids with solid volume fraction at higher temperatures is greater than that at lower temperature. Moreover, it can be also seen that the variation of thermal conductivity enhancement of nanofluids with temperature at higher solid volume fraction is more than that at lower solid volume fraction. Finally, based on experimental data, in order to predict the thermal conductivity ratio of ZnO–TiO2/EG hybrid nanofluids, a correlation was proposed. Deviation analysis of the thermal conductivity ratio was also performed. Comparison between experimental data and the proposed correlation outputs revealed that this correlation has a good accuracy.

Erratum to: Study on thermal conductivity of water-based nanofluids with hybrid suspensions of CNTs/Al2O3 nanoparticles

The aim of this work was to investigate the effects of temperature and solid volume fraction on thermal conductivity of CNTs–Al2O3/water nanofluids. Both Al2O3 nanoparticles and CNTs are dispersed in the base fluid with equal solid volume. Experiments were conducted with various solid volume fractions of 0.02, 0.04, 0.1, 0.2, 0.4, 0.8 and 1.0 % and various fluid temperatures of 303, 314, 323 and 332 K. Measured data reveal that the thermal conductivity of nanofluid highly depends on the solid volume fraction. Also, temperature may play an important role in enhancing thermal conductivity of CNTs–Al2O3/water, especially at high solid volume fractions. Based on experimental data, correlations are proposed for different temperatures by nonlinear regression. These correlations are able to predict thermal conductivity of nanofluid with high precision. Besides, a general correlation of thermal conductivity with function of temperature and solid volume fraction was proposed.

Effects of temperature and nanoparticles concentration on rheological behavior of Fe3O4–Ag/EG hybrid nanofluid: An experimental study

In this paper, the effects of temperature and nanoparticles concentration on the rheological behavior of Fe3O4–Ag/EG hybrid nanofluid have been experimentally investigated. Stable and homogeneous suspensions were prepared in solid volume fractions of 0.0375%, 0.075%, 0.15%, 0.3%, 0.6% and 1.2%. Viscosity measurements were performed at different shear rates (12.23–122.3s−1) under temperatures ranging from 25°C to 50°C. Results revealed that the nanofluid samples with solid volume fractions of less than 0.3% had Newtonian behavior, while those with higher solid volume fractions (0.6% and 1.2%) had non-Newtonian behavior, and followed the power-law model. Finally, the consistency index and power-law index were obtained from curve-fitting on shear stress–shear rate dependency. Curve-fitting results showed that all power-law indices were in the range of 0.5339–0.6706, indicating that the nanofluid samples possessed shear-thinning behavior at all temperatures considered.

Numerical studies of the effects of fines on fluidization

Euler‐Lagrange simulations of fluidized beds of Geldart Group A particles containing different levels of fines are performed in periodic domains with various domain‐averaged solid volume fractions. Bubble‐like voids readily form when no fines are added. Introducing fines does not reduce bubble sizes if van der Waals force between particles is not accounted for. In contrast, the addition of van der Waals force produces significant changes. With no fines, bubbles are found to be suppressed at sufficiently high solid volume fractions, corresponding to the expanded bed regime for Group A particles. With the addition of fines, bubbles can be suppressed at lower solid volume fractions. With more fines added, bubbles can be suppressed at even lower solid volume fractions. When bubbles are suppressed, the system is found to be in a stable solid‐like regime. In this regime, forces on each particle are balanced, and the particle velocity fluctuations are dampened. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2271–2281, 2016

Simulated configurational temperature of particles and a model of constitutive relations of rapid-intermediate-dense granular flow based on generalized granular temperature

In gas–solid flat-base spout bed with a jet, the flow of particles must go through an intermediate regime where both kinetic/collisional and frictional contributions play a role. In this paper, the statistical framework is proposed to define the generalized granular temperature which sums up the configurational temperature and translational granular temperature. The configurational temperature, translational and rotational granular temperatures of particles are simulated by means of CFD-DEM (discrete element method) in a 3D flat-base spout bed with a jet. The configurational temperatures of particles are calculated from instantaneous overlaps of particles. The translational and rotational granular temperatures of particles are calculated from instantaneous translational and angular velocities of particles. Roughly, the simulated translational and rotational granular temperatures increase, reach maximum, and then decrease with the increase of solids volume fractions. However, the configurational temperature increases with the increase of solids volume fractions. At high solid volume fraction, the predicted configurational temperatures are larger than the translational and rotational granular temperatures, indicating that the rate of energy dissipation do contributes by contact deformation of elastic particles. The generalized granular temperature is proposed to show the relation between the variance of the fluctuation velocity of deformation and the variance of the translational fluctuation velocity of particles. The constitutive relations of particle pressure, viscosity, granular conductivity of fluctuating energy and energy dissipation in rapid-intermediate-dense granular flows are correlated to the generalized granular temperature. The variations of particle pressure, shear viscosity, energy dissipation and granular conductivity are analyzed on the basis of generalized granular temperature in a flat-base spout bed with a jet. The axial velocities of particles predicted by a gas–solid two-fluid model of rapid-intermediate-dense granular flows agree with experimental results in a spout bed.

Breakup of high solid volume fraction oil–particle cluster in simple shear flow

Abstract Experiments were conducted of the low-Reynolds number breakup and separation of oil–particle clusters characterized by a high volume fraction of relatively large solid particles, under simple shear in an aqueous solution. The breakup of such oil–particle clusters, and the separation of particles from the clusters, are evaluated as a function of viscosity ratio of the oil phase to the aqueous solution, interfacial tension, and shearing time. When the viscosity ratio is high, clusters are more difficult to breakup, a longer shear time is needed, and few particles detach. At low viscosity ratios, clusters are easily deformed and break up into smaller clusters, and more clean particles detach. Lowering the interfacial tension also facilitates the liberation of oil droplets from particles. The results show that the breakup of oil–particle clusters with a high volume fraction of large particles can be characterized as simple droplet breakup, meaning that the viscosity of the oil governs the dynamics of the cluster, rather than an effective viscosity that is a function of the solid volume fraction. The degree of cluster breakup and the separation of particles from the primary cluster is related to a cluster-based capillary number and the viscosity ratio. There is a critical capillary number required to obtain clean particles.

Measurement of Mechanical Coherency Temperature and Solid Volume Fraction in Al-Zn Alloys Using In Situ X-ray Diffraction During Casting

During solidification of metallic alloys, coalescence leads to the formation of solid bridges between grains or grain clusters when both solid and liquid phases are percolated. As such, it represents a key transition with respect to the mechanical behavior of solidifying alloys and to the prediction of solidification cracking. Coalescence starts at the coherency point when the grains begin to touch each other, but are unable to sustain any tensile loads. It ends up at mechanical coherency when the solid phase is sufficiently coalesced to transmit macroscopic tensile strains and stresses. Temperature at mechanical coherency is a major input parameter in numerical modeling of solidification processes as it defines the point at which thermally induced deformations start to generate internal stresses in a casting. This temperature has been determined for Al-Zn alloys using in situ X-ray diffraction during casting in a dog-bone-shaped mold. This setup allows the sample to build up internal stress naturally as its contraction is prevented. The cooling on both extremities of the mold induces a hot spot at the middle of the sample which is irradiated by X-ray. Diffraction patterns were recorded every 0.5 seconds using a detector covering a 426 × 426 mm2 area. The change of diffraction angles allowed measuring the general decrease of the lattice parameter of the fcc aluminum phase. At high solid volume fraction, a succession of strain/stress build up and release is explained by the formation of hot tears. Mechanical coherency temperatures, 829 K to 866 K (556 °C to 593 °C), and solid volume fractions, ca. 98 pct, are shown to depend on solidification time for grain refined Al-6.2 wt pct Zn alloys.

Computational study of granular shear flows of dry flexible fibres using the discrete element method

In this study, shear flows of dry flexible fibres are numerically modelled using the discrete element method (DEM), and the effects of fibre properties on the flow behaviour and solid-phase stresses are explored. In the DEM simulations, a fibre is formed by connecting a number of spheres in a straight line using deformable and elastic bonds. The forces and moments induced by the bond deformation resist the relative normal, tangential, bending and torsional movements between two bonded spheres. The bond or deforming stiffness determines the flexibility of the fibres and the bond damping accounts for the energy dissipation in the fibre vibration. The simulation results show that elastically bonded fibres have smaller effective coefficients of restitution than rigidly connected fibres. Thus, smaller solid-phase stresses are obtained for flexible fibres, particularly with bond damping, compared with rigid fibres. Frictionless fibres tend to align with a small angle from the flow direction as the solid volume fraction increases, and fibre deformation is minimized due to the alignment. However, jamming, with a corresponding sharp stress increase, large fibre deformation and dense contact force network, occurs for fibres with friction at high solid volume fractions. It is also found that jamming is more prevalent in dense flows with larger fibre friction coefficient, rougher surface, larger stiffness and larger aspect ratio.

Influence of SLM on shape memory and compression behaviour of NiTi scaffolds

Octahedron-shaped porous scaffolds made from shape memory nickel–titanium (NiTi) were manufactured with different solid volume fractions using selective laser melting (SLM). Various SLM parameters were selected to affect the mechanical behaviour and shape memory response. It was shown that high laser power with high scanning speed (HP) parameters reduced the martensitic transformation temperatures as compared to low laser power low scanning speed (LP) parameters, resulting in an increased pseudoelastic behaviour (due to presence of austenite at room temperature). HP parameters, however, led to a larger geometrical mismatch with the original design and a higher solid volume fraction. The compression behaviours were also analysed and exhibited in correlation with the volume fractions.

Numerical Simulation of Modified Trailing Edge of Francis Turbine Stay Vane Based on Solid-Liquid Two-Phase Flow

In order to investigate the silt abrasion of modified trailing edge of stay vane in Francis turbine, the numerical simulation of trailing edge with different geometries were carried out based on the solid-liquid two-phase flow by means of Computation Fluid Dynamics. The results show that low solid volume fraction distributes on the chamfered surface of trailing edge, and high solid volume fraction distributes on the end of oblique surface. The smaller the modified angle is, the larger the distribution area of high solid volume fraction is, which show the trailing edge with smaller oblique angle may suffer from silt abrasion. Therefore, in order to solve the vibration caused by Karman vortex the trailing edge has to be sharpened, the oblique angle of trailing edge should not be too small. At end of trailing edge needs to ensure a certain thickness, especially the trailing edge near the lower ring can be thicker, which can meet the anti-abrasion requirements.

English

Materials deforms in response to an externally applied stress. The deformation can be permanent or temporary. Permanent deformation stays after the removal of the applied stress, while temporary deformation disappears on the removal of the stress. Both temporary and permanent deformations can be functions of time or virtually independent of time. Processing and handling of intermediate or final products involving particulate materials dispersed in liquid media at high solids volume fraction means Soft-Solids, present major challenges in the chemical industry and in its allied sections, such as; Biochemical and Biotechnology apparently the drugs and Pharmaceuticals industries. In the development of new processes, manufactures are faced with growing diversity of equipment options and a limited technical basis for selection, of their complex flow behaviour and the influence of the wall boundary conditions. Pilot scale trials may be lengthy, expensive and has to rely on uncertain rules of modelling scale-up. Therefore the current strategy which is emerging world-wide is to employ computer simulation as a basis for optimising the design and operating parameters. Importantly, soft-solids exhibit complex bulk flow and interfacial properties; that leads to the requirement for accurate and reliable constitutive information to model their processing. To obtain useful experimental data, there is a need for a well characterised and reproducible material. The „BEST‟ material will undergo sufficient plastic flow so as to be capable of being formed. Therefore a model paste Plasticine for Simulation and Terracotta for Modelling has been tested by CONE indenter over a wide range of strain rates. It was found that the terracotta exhibits a linear elastic behaviour at low stress levels and power law creeping behaviour at higher levels of stress. All the loading and relaxation tests at various strain-rates give the same material properties. This means that the model works reasonably well. The analysis of loading and relaxation is simple robust and easily provides a value of E, and the flow curve, this is also true for CONE indentation of soft-solids. The primary aim of this project was to attempt for developing and evaluating codes of the Finite Element Analysis (FEA) which are specifically designed for paste system. The finite element method has been shown to be viable computational tool for modelling pastes and the effects of the friction. However the practicality of the data method is very much dependent upon the accurate modelling of the paste behaviour. The predicted results, in some cases, show a reasonable agreement with those obtained experimentally.

Prediction of configurational and granular temperatures of particles using DEM in reciprocating grates

The configurational temperature and granular temperature of particles are simulated by means of discrete element method (DEM) in the reciprocating grate. Motion of mono-sized particles in the reciprocating grate is predicted with the change of frequency and amplitude of moveable grates. The distributions of velocity and volume fraction of particles are obtained. The granular temperature and configurational temperature of particles are calculated from simulated instantaneous velocities and overlaps of particles in a reciprocating grate. The simulated results show that the granular temperatures of particles increase, reach maximum, and then decrease with the increase of solids volume fractions. While the configurational temperature of particles is monotonously increased with the increase of solids volume fraction, indicating that the rate of energy dissipation contributes by deformation of elastic particles at high solids volume fraction. The influence of amplitude and frequency on granular temperature and configurational temperature is analyzed.

Numerical Simulation of Flow Through Circular Array of Cylinders Using Multi-Body and Porous Models

Two two-dimensional (2D) models for flow through a circular patch of circular cylinders in a channel, the multi-body model and porous model, are established using the scale adaptive simulation (SAS) turbulent model. It is verified that the multi-body model could predict well the average velocity field, turbulent structures and vortex in all cases. The porous model could only predict well the flow pattern and the large-scale vortex motion and fails to predict the small-scale motion. For cases of high solid volume fraction or low cylinder Reynolds number, the differences in prediction between the two models are small even in the region inside the patch. For the case of low solid volume fraction, the performance of the porous model is acceptable only in the region away from the patch. If predictions are required only for large-scale motion away from the patch, the more computational efficient porous model is a good modeling tool.

The dynamics of interfaces during coarsening in solid–liquid systems

The isothermal coarsening of dendritic Al–Cu microstructures is examined using time-resolved, in situ synchrotron-based X-ray tomographic microscopy. By obtaining the data at the coarsening temperature (in situ) with speeds that are on the order of or faster than the ongoing evolution of the microstructure (time-resolved, 4-D), we examine the dynamic morphological evolution of the solid–liquid interfaces in two solid volume fractions; as such, the relationship between the velocity of the evolving interface and characteristics that define the morphology of the interface is determined. We find that, while there is a correlation between velocity and mean curvature of the interface, there is a significant dispersion in the velocities for a given value of mean curvature. In addition, the Gaussian curvature plays a role in determining the interface velocity even though it has no effect on the chemical potential at the interface. We find that there are many interface patches of various morphologies and size scales that are not evolving during the coarsening process. At higher solid volume fractions and longer coarsening times, more of the structure is active in the coarsening process, and there is an increase in localized diffusional interactions.

Prediction of extrusion load and liquid phase filtration during ram extrusion of high solid volume fraction pastes

For perfect and homogeneous plastic materials, the extrusion stress and flow typology have previously been well described. However for firm pastes, during extrusion, liquid phase migration may appear leading to unsuccessful processing. Reviewed literature explains that there is a competition between the extrusion velocity and the liquid filtration velocity (or time).The aim of this work is to develop a new model to predict the ram extrusion force of frictional plastic materials such as firm fresh cement-based materials or clay pastes. A quantitative one-dimensional model based on consolidation theory has been developed to predict the extrusion force and quantify liquid phase migration.Model results are compared with experimental data from tests carried out on kaolin paste undergoing ram extrusion. Influences of extrusion rate, rheological parameters and filtration characteristics on extrusion load are investigated.

Granular shear flows of flat disks and elongated rods without and with friction

Granular shear flows of flat disks and elongated rods are simulated using the Discrete Element Method. The effects of particle shape, interparticle friction, coefficient of restitution, and Young's modulus on the flow behavior and solid phase stresses have been investigated. Without friction, the stresses decrease as the particles become flatter or more elongated due to the effect of particle shape on the motion and interaction of particles. In dense flows, the particles tend to have their largest dimension aligned in the flow direction and their smallest dimension aligned in the velocity gradient direction, such that the contacts between the particles are reduced. The particle alignment is more significant for flatter disks and more elongated rods. The interparticle friction has a crucial impact on the flow pattern, particle alignment, and stress. Unlike in the smooth layer flows with frictionless particles, frictional particles are entangled into large masses which rotate like solid bodies under shear. In dense flows with friction, a sharp stress increase is observed with a small increase in the solid volume fraction, and a space-spanning network of force chains is rapidly formed with the increase in stress. The stress surge can occur at a lower solid volume fraction for the flatter and more elongated particles. The particle Young's modulus has a negligible effect on dilute and moderately dense flows. However, in dense flows where the space-spanning network of force chains is formed, the stress depends strongly on the particle Young's modulus. In shear flows of non-spherical particles, the stress tensor is found to be symmetric, but anisotropic with the normal component in the flow direction greater than the other two normal components. The granular temperature for the non-spherical particle systems consists of translational and rotational temperatures. The translational temperature is not equally partitioned in the three directions with the component in the flow direction greater than the other two. The rotational temperature is less than the translational temperature at low solid volume fractions, but may become greater than the translational temperature at high solid volume fractions.

Phase field modeling of the influence of interfacial wettability and solid volume fraction on the kinetics of coarsening

Coarsening of solid particles in a solid-liquid two-phase system with high solid volume fraction is studied using the multiphase-field model. The influences of interfacial wettability and solid volume fraction on growth exponent, coarsening rate, and particle size distribution (PSD) are analyzed. It is found that the growth exponent is independent of the volume fraction, while the coarsening rate constant and the PSD are closely related to the interfacial wettability and the solid volume fraction. Under the completely wetting condition the coarsening rate constant increases with volume fraction increasing, but this variation is insignificant under the incompletely wetting condition. Moreover, when the wettability is low and volume fraction is high, the coarsening rate may also decrease with volume fraction increasing. The simulation results also show that with the increase of volume fraction, the peak frequency decreases and the PSD becomes broader, but the fall of the peak frequency under the incompletely wetting condition is slower than under the completely wetting condition. The simulation results provide an insight into the discrepancy between different experimental observations.