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Predictions of clarified layer depth and solids suspension in a draft tube reactor were investigated at a moderate solids loading of 16% v/v using both a RANS approach (k − ε) and a scale-resolving approach using Stress Blended Eddy Simulation (SBES). The multiphase flow was modelled using an Algebraic Slip model and the impact of drag law, turbulent particle diffusion and number of particle size classes was examined. The inclusion or exclusion of turbulent particle diffusion is found to dominate the RANS results, with resulting poor prediction of clarified layer depth and solids suspension under some conditions. In contrast, the SBES model is found to give good agreement with experimental data and the results show there is no need for a modelled turbulent dispersion force in this system if the large-scale turbulence structures responsible for particle transport are explicitly resolved. [Display omitted] • Clarified layer depth and solids suspension in a draft tube reactor studied. • RANS and Stress Blended Eddy Simulation (SBES) predictions compared. • Impact of modelled turbulent dispersion force investigated. • SBES predictions superior to RANS and in close agreement with experimental data. [ABSTRACT FROM AUTHOR]

The particle suspension velocity has a strong practical impact on pneumatic conveying systems. The barycenter and centroid of large nonspherical particles are not in the same point, and the particles rotate under the action of torque when the particles are subjected to an unbalanced force in the flow field. This rotation causes the vortexes or turbulence near the particles. The stirring effect of large particle is especially obvious and directly affects the particle suspension behavior. To investigate the suspension behavior of large (5–30 mm) nonspherical particles in vertical pneumatic conveying, the CFD-DEM coupling method is adopted to realize the coupling between the solid phase and the gas phase and establish the coupling simulation model between the nonspherical particles and flow field. The suspension velocity relations of three flow drag zones are calculated on the basis of the particle-size method and the relationships between the pipe diameter, particle shape, Reynolds number and fluid drag coefficient. It will help in designing and operation of pneumatic conveying systems. The dynamic characteristics of large nonspherical particles in the vertical flow field are analyzed according to the particle suspension experiment and simulation results. The experiment and simulation results show that the nonspherical particles rotate in the vertical flow field, which can reduce the required flow velocity of large nonspherical particles in vertical pneumatic conveying. Unlabelled Image • The relations between particle diameter and suspension velocity are obtained. • The particle irregular shape causes the rotational motion in experiment. • The pressure gradient of flow field causes the particle rotation in simulation. • The flow drag of flow field changes with particle windward area. • Rotational motion reduces flow velocity required for vertical pneumatic conveying. [ABSTRACT FROM AUTHOR]

Suspensions of an elliptical particle in Poiseuille flow are investigated by using the multiple-relaxation-time lattice Boltzmann method coupled with the Galilean-invariant momentum exchange method. The elliptical particle shows lateral migration and final equilibrium, which are similar to the classical Segré–Silberberg effect. Because the elliptical shape interacts with the parabolic velocity distribution of the Poiseuille flow, the particulate behaviors remarkably contain regular wave accompanied by nonuniform rotation. When the blockage ratio grows up, the equilibrium position of the particle moves towards the channel centerline and the rotation period becomes long. With the increase of the aspect ratio, the rotation period becomes short; the equilibrium position shows a shape of saddle and reaches its bottom at nearby aspect ratio 0.5. Surprisingly, the numerical results show that the equilibrium position is insensitive to Reynolds number (Re) of Poiseuille flows in the range 3 ≤ R e ≤ 300. This work can make active promotions to the researches of blood circulation of birds, whose red blood cell is oval or elliptical in shape. [ABSTRACT FROM AUTHOR]

Highlights • We study particle migration in the flow of apparent yield-stress fluids. • A new regularized viscosity function for viscoplastic behavior is presented. • The regularization leads to a particle-free plug flow at steady-state conditions. • Apparent yield-stress materials enhance the particle flux towards the tube wall. Abstract Suspensions of particles with viscoplastic characteristics are often found both in nature and industrial applications. However, in contrast with the case of suspensions in Newtonian fluids, the dynamics of shear-induced particle migration in yield-stress suspending materials is not yet fully understood. In this work, we present a numerical study of particle migration in pressure-driven, tube flows of suspensions of non-colloidal, spherical particles dispersed in apparent yield-stress fluids. The suspension viscosity is modeled using the classical Krieger–Dougherty equation with a novel regularized viscosity function for viscoplastic materials as the suspending medium viscosity, and the dynamics of shear-induced particle migration is described with the Diffusive Flux Model. The resulting fully coupled, non-linear, one-dimensional model is solved with a second-order finite difference scheme coupled with Newton's method. We present a parametric study that elucidates the role played by the suspension bulk concentration, Plastic number, and power-law index on the velocity profile and particle concentration distribution in the flow. Remarkably, the results show that particle migration in apparent yield-stress fluids leads to a strikingly different pattern of velocity and particle distribution profiles relative to the case of suspensions in Newtonian liquids and true yield-stress materials. [ABSTRACT FROM AUTHOR]

Abstract Radioactive liquid waste is often stored in a large capacity (150 m 3 ) horizontal cylindrical tanks. It is necessary to keep the contents of the tank agitated to prevent the settling of fine solids in the tank. In extreme cases, solids settled at the tank base may invoke the system malfunction. This paper deals with the Computational Fluid Dynamic (CFD) modeling of the agitation mechanism considering the turbulent dispersion effects. The simulations are conducted on a standard tank geometry to arrive the optimum jet velocity required to suspend the settled solid particles thoroughly. The distribution of volume phase fraction, velocity magnitude, turbulence kinetic energy (TKE) and eddy dissipation of each phase for different inlet jet velocities (v = 10–25 m / s) have been presented. The spatial variation of these quantities are measured at three different planes in the vessel mainly in the vicinity of the nozzle exit. The results indicate that the jet velocity is a significant parameter that influences the particle suspension. Parametric studies have also been carried out for four different particle sizes, viz. d p = 5, 10, 50 and 100 μ m. The present study revealed that, for the range of parameters covered, the smallest ( d p = 5 μ m) and the largest ( d p = 100 μ m) particle sizes has least effect in terms of solids suspension. Highlights • Jet agitation for solid particle suspension is numerically studied. • The influence of jet velocity and particle size on the flow characteristics is investigated. • This analysis revealed a counter rotating vortex pair originated from the nozzle tip. • Optimal jet parameters are obtained by performing systematic numerical simulations. [ABSTRACT FROM AUTHOR]

Rate capability is a critical metric for assessing lithium-ion battery materials, especially in the electric vehicle industry which requires high battery power density. The typical method for rate capability evaluation of battery materials involves electrode processing, battery assembly, and testing on a battery cycler with varying current rates. This method is very important in evaluating battery materials, however, it is time-consuming and depending on the cell type can take days to weeks. Rate capability can also be affected by other factors besides the active material properties including electrode slurry homogeneity, contact junctions formed during battery assembly, and the connectivity of the interfaces within the battery electrodes. Herein, we will describe the use of a technique termed dispersed particle resistance (DPR) to evaluate the battery cathode active material LiCoO 2 (LCO), the first layered oxide evaluated using this method. This new technique works relatively fast, providing qualitative analysis within several minutes, and does not require electrode fabrication or additional materials in the system besides a carrier fluid for the electrolyte. While DPR does not explicitly give rate capability of the materials, DPR was successfully demonstrated to provide the relative rate capability for multiple different LCO samples, as supported by the results obtained from conventional rate capability testing using cycling data. Additionally, the physical properties of the material probed by the DPR were investigated by determining the lithium diffusivity in the crystal structure of the different LCO materials with galvanostatic intermittent titration technique. [ABSTRACT FROM AUTHOR]

The key to achieve an economically more attractive concentrated solar power plant is to work at higher operating temperatures, allowing both higher power conversion efficiencies resulting in a smaller heliostat field for a given energy output, and higher temperature ranges in the storage tanks, with increased energy storage density and smaller size, hence less expensive. This fostered the development of using particle suspensions as heat transfer media. This paper presents a theoretical framework for the energy analysis of a particle-in-tube solar power plant, hybridized, with topping air-Brayton cycle turbine, and bottoming steam block. From studying the effects of essential design parameters on the energy efficiency, the heat transfer efficiency of the turbine air preheater is of paramount importance to increase the solar contribution within the hybrid concept, while the energy efficiency moreover increases by an optimum air-Brayton cycle turbine operation (mostly through the pressure ratio, less by the operating temperature). The overall efficiency of the concept varies from about 40% when using combined low and high pressure Brayton cycle turbines only, to over 48% in a fully combined air-steam concept. Energy efficiency findings are in agreement with the literature data. [ABSTRACT FROM AUTHOR]

[Display omitted] • A scheme was proposed to realize the harmless motion and accumulation of particles. • The particle suspension was effectively suppression, improving product quality and production efficiency. • The research can provide a basis of field productions concerning control technologies of particles. Particle suspension in a turbulent flow can seriously affect the performance of manufactured products in many industrial processes in which the motion of particles cannot be modeled using the numerical method because of the enormous number of particles. Therefore, in this study, a full-scale computational fluid dynamics (CFD) simulation and a 1/5 scaled-down water model experiment were employed to investigate the flow pattern and dynamic behavior of particles in a continuously stirred vessel system. Based on the understanding of the suspension mechanism of settling particles, a particle-suppression device was designed to realize the harmless movement and deposition of particles. The results showed that the flow guidance and division mechanisms of the particle-suppression device led to the inhibition of particle suspensions. In addition, the optimal parameter combination for the device from the water model experiment combined with the orthogonal experimental design, resulted in a 98.3% reduction in the concentration of suspended particles. The suspension of particles was effectively suppressed, which improves product quality and production efficiency. Reliable results can be achieved by combining CFD simulations and water model experiments. [ABSTRACT FROM AUTHOR]

Battery active materials are evaluated using numerous material characterization techniques for fundamental understanding, comparative analysis during research and development, and for quality control during manufacturing. Electrochemical properties of the active materials also need to be investigated and validated, and this analysis is very time and material intensive generally requiring electrode fabrication, cell assembly and cell cycling. In addition, evaluating active materials electrochemically in battery cells can be complicated by the electrode microstructure and the contributions of other components within the cell that are not the active materials. In this report, an active material characterization method is demonstrated to provide electrochemical insights for lithium-ion cathode materials by dispersing them into aqueous electrolyte and flowing through an electrochemical reaction cell. This method requires very little active material and time to conduct the measurements, typically requiring under 0.1 grams of material and less than 10 minutes. The measured resistance from this technique provides insights into the electrochemical performance of the active material and generally correlates to the rate capability. This measured resistance is insensitive to other electrode components or electrode microstructure because there is no electrode fabrication step. LiFePO 4 was chosen as a commercial material for initial demonstration of the technique. [ABSTRACT FROM AUTHOR]

Slot coating is a common method in the manufacturing of a wide variety of functional films. In many applications, the coating liquid is a particle suspension and the performance of the final product is directly related to the micro structure of the film. Fundamental understanding of the suspension flow enables a better control of the particle distribution on the coated layer and, consequently, on the coating process and product performance optimization. A common simplified approach to study coating flow of non-colloidal particle suspension is to consider that the particles are uniformly distributed in the coating bead and that the liquid viscosity is constant and equal to the value of the bulk concentration. However, experimental evidences have shown that shear-induced migration leads to non-uniform particle distribution. The literature presents numerical predictions on surface inactive, neutrally buoyant particle suspension flow which have shown that particle distribution in the coated layer strongly depends on the process conditions. Here, we extend the previous analyses to explore the effect of different process conditions, including the effect of particle sedimentation and Marangoni stresses caused by surface-active particles. Results show how particle distribution changes with flow conditions and particle properties, and that Marangoni stresses can change the recirculation pattern of the flow. [ABSTRACT FROM AUTHOR]

Large-scale human mesenchymal stem cell expansion calls for a bioreaction system, that provides a sufficient growth surface. An alternative to static cultivations systems like cell factories are disposable stirred tank reactors. Here, microcarriers provide the required growth surface, but these make it difficult to achieve a complete homogenization in the bioreactor, while avoiding shear stress. To gain insight into this process, we investigated the impact of different power inputs (0.02–2.6 W m −3 ) on the mixing time (t m ). Whereas t m was inversely proportional to agitation in a one-phase-system, aeration resulted in a constant mixing time at 30–70 rpm. A high microcarrier concentration (30 g L −1 ) and low stirrer speed (30 rpm) in the liquid-solid system caused a 50-fold increase in t m and the formation of a discrete non-mixed upper zone. The effect of the microcarrier concentration on t m became negligible at higher stirrer speeds. In the three-phase system, microcarrier settling was prevented by aeration and a minimal specific power input of 0.6 W m −3 was sufficient for complete homogenization. We confirmed that a low power input during stem cell expansion leads to inhomogeneity, which has not been investigated in the three-phase system up to date. [ABSTRACT FROM AUTHOR]

The suspension of a heavy sphere by an upward jet is a classical fluid mechanics experiment to demonstrate the fluid forces acting on an object. In the range of the parameter space where the sphere can be suspended, the dynamics can either be regular, i.e., with oscillations around an equilibrium position, or chaotic, with extreme events leading to large deviations from that equilibrium region. The existence and characteristics of suspension regimes of several heavy spheres in such flow configurations remain open questions. Spheres compete for the equilibrium position and come very close to each other, resulting in large local particle concentrations that prevent direct imaging. Relatively high speed X-ray radiography along with the radioSphereanalysis technique is leveraged here to study the time-resolved 3D trajectory of each individual sphere in a vertical jet. radioSphereis an X-ray analysis method that retrieves the 3D information out of a single 2D radiography using a priori knowledge of the imaging geometry (E. Andò et al., 2021), which due to the imaging modality imposes no limitations on the optical properties of the water. The 3D ＋ time kinematics yield the evolution of the statistics of the position and velocity of the spheres as a function of the number of spheres and for two jet Reynolds numbers. Drastic changes in behavior occur when many spheres are present, leaving a clear signature on the temporal dynamics and on the exploration of the flow volume, where spheres can remain on the bottom of the vessel for long periods of time, resulting in only partial suspension. In addition to the suspension capacity, the interactions between spheres are explored with statistics of pair separation distances, which, together, allow for quantitative arguments to introduce suspension regimes of a collection of spheres in an upward vertical jet. • The suspension dynamics of heavy spheres in an upward vertical jet are studied. • Time-resolved radiography combined with the radioSphere method yields 4D kinematics. • Statistics of the spheres' position and velocity and temporal dynamics are explored. • The interactions between spheres drastically change the dynamics and flow sampling. • Collective suspension regimes are introduced quantitatively based on interactions. [ABSTRACT FROM AUTHOR]

Multiphase displacement in porous media can be adjusted by micro/nanoparticle suspensions, which is widespread in many scientific and industrial contexts. Direct visualization of suspension flow dynamics and corresponding multiphase patterns is crucial to understanding displacement mechanisms and eventually optimizing these processes in geological, biological, chemical, and other engineering systems. However, suspension flow inside the opaque realistic porous media makes direct observation challenging. The advances in microfluidic experiments have provided us with alternative methods to observe suspension influence on the interface and multiphase flow behaviors at high temporal and spatial resolutions. Macroscale processes are controlled by microscale interfacial behaviors, which are affected by multiple physical factors, such as particle adsorption, capillarity, and hydrodynamics. These properties exerted on the suspension flow in porous media may lead to interesting interfacial phenomena and new displacement consequences. As an underpinning science, understanding and controlling the suspension transport process from interface to flow patterns in porous media is critical for a lower operating cost to improve resource production while reducing harmful emissions and other environmental impacts. This review summarizes the basic properties of different micro/nanoparticle suspensions and the state-of-the-art microfluidic techniques for displacement research activities in porous media. Various suspension transport behaviors and displacement mechanisms explored by microfluidic experiments are comprehensively reviewed. This review is expected to boost both experimental and theoretical understanding of suspension transport and interfacial interaction processes in porous media. It also brings forward the challenges and opportunities for future research in controlling complex fluid flow in porous media for diverse applications. [Display omitted] • A comprehensive review of progress on microfluidic experiments for micro/nanoparticles suspension-related multiphase displacement mechanism. • The microscopic particle kinetics and the basic properties of different micro/nanoparticle suspensions are summarized. • The state-of-the-art microfluidic techniques for displacement research activities in porous media are reviewed. • Various suspension transport behaviors and corresponding displacement mechanisms in porous media are summarized and discussed. [ABSTRACT FROM AUTHOR]

This study examines the use of a lattice Boltzmann method framework to study heat transfer behaviours within particle suspensions. This has been done through the use of an adapted interface condition to attempt to resolve the required continuity of temperature and flux at the boundary between the solid and fluid phases. The proposed method is tested against analytical solutions for layered media in both a 1D bar and a radial layout. These tests showed that the model was able to generate results with first order convergence towards the analytical outcomes. The model was then used to examine the behaviour of two moving particles travelling along a channel to illustrate its potential for resolving complex suspension flows. [ABSTRACT FROM AUTHOR]

Large-scale human mesenchymal stem cell expansion calls for a bioreaction system, that provides a sufficient growth surface. An alternative to static cultivations systems like cell factories are disposable stirred tank reactors. Here, microcarriers provide the required growth surface, but these make it difficult to achieve a complete homogenization in the bioreactor, while avoiding shear stress. To gain insight into this process, we investigated the impact of different power inputs (0.02–2.6 W m −3 ) on the mixing time (t m ). Whereas t m was inversely proportional to agitation in a one-phase-system, aeration resulted in a constant mixing time at 30–70 rpm. A high microcarrier concentration (30 g L −1 ) and low stirrer speed (30 rpm) in the liquid-solid system caused a 50-fold increase in t m and the formation of a discrete non-mixed upper zone. The effect of the microcarrier concentration on t m became negligible at higher stirrer speeds. In the three-phase system, microcarrier settling was prevented by aeration and a minimal specific power input of 0.6 W m −3 was sufficient for complete homogenization. We confirmed that a low power input during stem cell expansion leads to inhomogeneity, which has not been investigated in the three-phase system up to date. [ABSTRACT FROM AUTHOR]

Biological tissues are characterised by spatially distributed gradients, intricately linked with functions. It is widely accepted that ideal tissue engineered scaffolds should exhibit similar functional gradients to promote successful tissue regeneration. Focusing on bone, in previous work we proposed simple methods to obtain osteochondral functionally graded scaffolds (FGSs), starting from homogeneous suspensions of hydroxyapatite (HA) particles in gelatin solutions. With the main aim of developing an automated device to fabricate FGSs, this work is focused on designing a stirred tank to obtain homogeneous HA–gelatin suspensions. The HA particles transport within the gelatin solution was investigated through computational fluid dynamics (CFD) modelling. First, the steady-state flow field was solved for the continuous phase only. Then, it was used as a starting point for solving the multi-phase transient simulation. CFD results showed that the proposed tank geometry and setup allow for obtaining a homogeneous suspension of HA micro-particles within the gelatin solution. [ABSTRACT FROM AUTHOR]

The influence of particles on the dynamics and eventual rupture of stretching liquid bridges is demonstrated experimentally in a drop-forming case. To analyze the particle-scale basis for the influence of particles in this flow, a lattice Boltzmann algorithm for a three-phase system of liquid, gas, and solid particles, has been developed. This provides full coupling between particles and fluids, fluid interfacial forces, and possible entry of particles into the interface (i.e. full and partial wetting by the liquid are considered). This work details the numerical method and its validation, and presents results of the simulations and related experiments. Fully-wetting particles up to a solid volume fraction of ϕ = 0.3 monotonically increased the rupture length of liquid bridges, as seen in experiments; experimental results show that the increase continues to a maximum at ϕ ≈ 0.4 , a condition beyond the present numerical capability. Depending on the wettability and volume fraction of the particles in the liquid bridge, particles can alter the structure of the bridge at pinch-off, suppress satellite drops, or produce asymmetrical pendant/sessile suspension drops as a result of their discrete nature. Particles with a neutrally wetting contact angle ( θ = 90 ° ) can reside in the bulk or be immersed in the interface if fluid deformation brings them into contact with it, and capillary forces are found to bring the interfacial particles near the narrow region (or “throat”) of the bridge prior to rupture. Fully wetting particles ( θ ≈ 0 ° ) remained interior to the liquid bridge, leaving less space to escape the throat region. Neutrally wetting particles increased the rupture length and altered the pinch-off structure relative to the particle-free case, but less so than fully wetting particles. [ABSTRACT FROM AUTHOR]

We studied the interactions among three circular particles suspended in a power-law fluid undergoing confined shear flow in two dimensions. The calculations are based on our previously developed lattice Boltzmann direct-forcing/fictitious-domain method. Reynolds numbers 1 ⩽ Re ⩽ 20 and power-law indices 0.5 ⩽ n ⩽ 1.5 were considered. We roughly classified the particles’ motion into “returning” and “passing” behaviors. We found that the particles are more likely to pass for higher Reynolds numbers or lower power-law indices, given the same flow conditions. In particular, we investigated the dynamics of the particles in shear flows and find two peaks in the horizontal fluid (drag) force for large Reynolds number or small power-law index. The first peak serves to decelerate the particles, while the second does the opposite, and might be primarily responsible for the transition from the “returning” to the “passing” behavior. We also studied the effects of the Reynolds number and the power-law index on particle velocity and streamline patterns. [ABSTRACT FROM AUTHOR]

In this study, steady and unsteady magneto-hydrodynamic (MHD) Couette flows between two parallel infinite plates have been studied through numerical Differential Quadrature Method (DQM) and analytical Differential Transformation Method (DTM), respectively. Coupled equations by taking the viscosity effect of the two phases for fixed and moving plates have been introduced. The precious contribution of the present study is introducing new, fast and efficient numerical and analytical methods in a two-phase MHD Couette fluid flow. Results are compared with those previously obtained by using Finite Difference Method (FDM). The velocity profiles of two phases are presented and a parametric study of physical parameters involved in the problem is conducted. As an outcome, when magnetic source is fixed relative to the moving plate, by increasing the Hartmann number, velocity profiles for both phases increased, but when it is fixed relative to the fluid an inverse treatment is observed. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we present the mass transfer during the buoyant CO2 bubble absorption in a particle suspension by the experimental and computational studies. In the experimental study, the transient evolution of a single bubble behavior is visualized for the CO2 absorption in Al2O3-nanofluids. In the computational study, the finite element approximated Navier–Stokes equations are employed integrating with a level set method for tracking the interface on the convective diffused mass transfer in a CO2 bubble with the multi-freely suspended non-Brownian Al2O3-particles. In both approached studies, the particle hydrodynamic effect to the bubble motion takes effect on increasing the mass transfer area followed by inducing the mass transfer enhancement (MTE) by a term of the larger mass transfer coefficient (MTC) at the gas–liquid phase. From computational study, this is also supported that the enhanced mass flux is highly influenced by the particle hydrodynamics on the bubble surface in a buoyant bubble. Consequently, it can lead to find an existence as one of possible mechanisms for MTE on a gas-absorption in a suspension. [Copyright &y& Elsevier]

Abstract: Pollution of water is a matter of concern all over the earth. Particles are known to play an important role in the transportation of pollutants in this medium. In addition, the emergence of new materials such as NOAA (Nano-Objects, their Aggregates and their Agglomerates) emphasizes the need to develop adapted instruments for their detection. Surveillance of pollutants in particulate form in waste waters in industries involved in nanoparticle manufacturing and processing is a telling example of possible applications of such instrumental development. The LIBS (laser-induced breakdown spectroscopy) technique coupled with the liquid jet as sampling mode for suspensions was deemed as a potential candidate for on-line and real time monitoring. With the final aim in view to obtain the best detection limits, the interaction of nanosecond laser pulses with the liquid jet was examined. The evolution of the volume sampled by laser pulses was estimated as a function of the laser energy applying conditional analysis when analyzing a suspension of micrometric-sized particles of borosilicate glass. An estimation of the sampled depth was made. Along with the estimation of the sampled volume, the evolution of the SNR (signal to noise ratio) as a function of the laser energy was investigated as well. Eventually, the laser energy and the corresponding fluence optimizing both the sampling volume and the SNR were determined. The obtained results highlight intrinsic limitations of the liquid jet sampling mode when using 532nm nanosecond laser pulses with suspensions. [Copyright &y& Elsevier]

Abstract: This paper shows the effect of the hydrodynamic interactions between non-Brownian isotropic particles for mass transfer enhancement in a shear flow generated by sliding walls in two dimensions through the direct numerical simulations. The particles are considered as a separate phase, while suspending solvent is modeled using the Stokes equation of which inertial and buoyancy effect are neglected. In the numerical simulation, we employ the finite element method to discretize the spatial domain with an explicit time stepping method. Interface capturing method is used to identify the boundary between the particle and the fluid. Automated adaptive mesh refinement is employed to increase the resolution in the vicinity of the particle boundaries as well as the interface between the solute and solvent. We investigate the effect of the particle hydrodynamics on mass transfer when the solute transports into the solvent and compare the mass transfer enhancements as a function of area fraction of multi-non-Brownian particles contributed. It is found that the mass transfer is enhanced by 3.6% in 1.0% area fraction which is a critical particle area fraction for the present flow conditions. [Copyright &y& Elsevier]

Abstract: Numerical simulations of the interaction between two non-Brownian isotropic particles in a shear flow confined between two sliding plates in two and three dimensions are presented. The suspending fluid is modelled using the Oldroyd-B constitutive equation and so incorporates the effects of viscoelasticity and first normal stress difference, but not shear-thinning. The particles are treated as a separate phase within the simulation with automated adaptive mesh refinement used to increase the resolution near the particle boundaries. The finite element method is used to discretise the spatial domain with a discontinuous Galerkin approximation for polymer stress and is implemented using the deal.II object oriented library. We identify three distinct types of interaction in two-dimensional systems: pass, return and tumble. We also show that the interactions between two spheres in a three-dimensional shear flow is qualitatively similar to the interaction between two circular particles, for particles in the same vorticity plane. For oblique interactions we find a further type of behaviour, similar to the Jeffery orbits of rigid rods. [Copyright &y& Elsevier]

Abstract: Ultrasound particle sizing is attracting an increasing attention from academic research and industrial applications as it offers non-invasive, suitable for highly turbid and concentrated nanoparticle suspensions and potentially no sample dilution needed features. The main challenge to this technique is thought to be its capability of dealing with high concentration. Most ultrasound particle sizing techniques employ ECAH (Epstein, Carhart, Allegra and Hawley) theory based models for the inversion of ultrasound spectra to particle size distribution (PSD). However, this theory is based on “single particle scattering”, namely a single particle immersed in an infinite medium, it is therefore only valid when ultrasound attenuation and particle concentration are linearly related. With the increase of particle concentration, due to the interactions between particles, the relation between attenuation and concentration may become nonlinear for solid–liquid suspensions. This paper demonstrates a method using population balance (PB) modelling to deal with the high concentration PSD problem for silica suspensions. It concludes that with a de-aggregation model, it is possible to convert attenuation inverted PSDs (ECAH model based inversion) at high concentrations into the PSD that is thought to be the correct PSD at a critical low concentration by a PB simulation. [ABSTRACT FROM AUTHOR]

Abstract: We analyze the mechanical behavior of a two-phase system consisting of rigid grains and an interconnected pore fluid. For this purpose we use 2D direct numerical simulations on the spatial scale of individual grains for Newtonian and non-Newtonian fluid rheology. By using the stress–strain rate relation we derive scaling laws for effective viscosity of two-phase particle suspensions. We demonstrate that the effective rheology of the assemblage is non-Newtonian only if the fluid has a non-Newtonian rheology. At small fluid fraction, inter-granular strain rates are up to 3 orders of magnitude higher than the applied background strain rate. We suggest that this effect explains the experimentally observed change at higher strain rates in rheology, from Newtonian to non-Newtonian aggregate rheology. To establish the conditions at which the fluid–solid aggregate deforms coherently as a consequence of Rayleigh–Taylor instabilities we studied flow patterns of particle suspensions and characterized them as a function of fluid fraction, viscosity, density, shape and size of the grains. From initial conditions with homogeneously distributed grains and interstitial fluid above a layer of pure fluid, our results show that the Rayleigh–Taylor instability dominates for moderate to large fluid fractions. At large fluid fractions, we observed a transition to a Stokes suspension mode, in which grains do not interact but sink independently. An analytical expression is derived that predicts the transition from Rayleigh–Taylor instability to Stokes suspension mode. The transition is a function of fluid fraction, radius of the grains, height of the interface and initial amplitude. Systematic numerical simulations are in good agreement with the analytical predictions. [Copyright &y& Elsevier]

Abstract: Ink jet printing is an attractive route for the manufacture of small ceramic parts and MEMS components. The attainable feature size of a component fabricated in this fashion is determined by both the generated droplet size and how the droplet interacts with the substrate. Here we present a study of the impingement and coalescence of drops to form beads, and linear deposits after a subsequent phase change. Experimentally, it is found that there is a minimum width of linear deposit produced in this way that is dependent upon droplet size and the surface energy interaction between droplet and substrate. A simple geometric model is presented that can accurately predict both the onset of limitation with changing droplet separation and the width of the deposit at a given droplet separation. A bulging instability is also found at small droplet separation that is explained in terms of competing pressure-driven axial flow and spreading flow driven by capillarity. The bulging of deposited nanoparticulate ink was found to agree qualitatively with previous observations, with the bulging being reduced with increasing print-head traverse velocity. The bulging of deposited solution-based ink did not agree with previous observations; this was explained in terms of evaporation of solvent as the instability was formed. [Copyright &y& Elsevier]

Abstract: An averaged motion approach for modeling Brownian dynamics for suspension systems of electrically charged particles in liquid is developed. The continuum model for the motion of particles consists of a system of integral equations coupled with a degenerate parabolic equation. Existence and uniqueness of global solution for the coupled system are established, and numerical results for the non-Newtonian viscosity of the mixture in terms of shear rate or Pechlet number are obtained. The model reveals some non-Newtonian properties such as the well-known shear thinning phenomenon for the viscosity of colloidal dispersions. [Copyright &y& Elsevier]

In this work, the effect of the vessel bottom roughness on the suspension of solid particles in stirred tank reactors is investigated. The experiments were performed in a baffled vessel, which was mechanically stirred with a 45° pitched blade turbine. In order to evaluate the influence of the bottom roughness on particle suspension, four bottoms of different roughness and 8 different sets of spherical particles were used. The density of the solid particles, ρs, ranged from 2500 kg m−3 to 8743 kg m−3 and they were characterized by narrow size distributions with a mean diameter, dp, from 128 µm up to 1850 µm. Measurement of the minimum impeller speed for ‘just complete suspension’, Njs, showed that the roughness of the bottom had a significant influence. The precise effect depends on the particle size compared to the size of the roughness elements and to the Kolmogoroff microscale, λK. [ABSTRACT FROM AUTHOR]

Abstract: Certain classes of particulate suspensions, consisting of semi-conducting, solid particles dispersed in an insulating carrier liquid, show a dramatic increase in flow resistance when placed under an external electric field. These so-called “electro-rheological fluids” have potential application in engineering devices such as tunable vibration damping systems. Under the field, a yield stress is induced in the fluid, and the characterisation of this quantity is essential for the design of many engineering devices. A new method for determining the yield stress is presented, which involves subjecting the sample to a constant shear stress and monitoring its shear rate after a step change in the electric field. It is found that this step field method can reproducibly determine the field-induced yield stress of a suspension of silica particles in silicon oil. [Copyright &y& Elsevier]

We present a new finite element scheme for direct simulation of inertialess particle suspensions in simple shear flows of Oldroyd-B fluids. The sliding bi-periodic frame concept of Lees & Edwards [J. Phys. C 5 (1972) 1921] has been combined with the DEVSS/DG finite element scheme, by introducing constraint equations along the domain boundary. The force-free, torque-free rigid body motion of a particle is described by the rigid-ring problem and implemented by Lagrangian multipliers only on the particle boundary, which allows general treatments for boundary-crossing particles. In our formulation, the bulk stress is obtained by simple boundary integrals of Lagrangian multipliers along the domain and particles. Concentrating on 2-D circular disk particles, we discuss the bulk rheology of suspensions as well as the micro-structural developments through the numerical examples of single-, two- and many-particle problems, which represent a large number of such systems in simple shear flow. We report the steady bulk viscosity and the first normal stress coefficient, from very dilute to highly concentrated systems. The results show shear-thickening behavior for both properties and the common experimental observation of the scaling of the first normal stress to the shear stress has been reproduced. Unlike Newtonian systems, two particles in an Oldroyd-B fluid result in kissing-tumbling-tumbling phenomena: they keep rotating around each other, when they are closely located. Many-particle problems reveal the occurrence of strong elongational flows between separating particles. [Copyright &y& Elsevier]

• Interface-resolved simulations of heat transfer in particulate channel flow. • Laminar and turbulent flows with dilute to moderate solid volume fractions. • Identifying different regimes of heat transfer, diffusion or transport dominated. • We relate the heat transfer enhancement to the particle motion and distribution. • There exists an intermediate volume fraction leading to optimal transfer. We present results of interface-resolved simulations of heat transfer in suspensions of finite-size neutrally-buoyant spherical particles for solid volume fractions up to 35% and bulk Reynolds numbers from 500 to 5600. An Immersed Boundary–Volume of Fluid method is used to solve the energy equation in the fluid and solid phase. We relate the heat transfer to the regimes of particle motion previously identified, i.e. a viscous regime at low volume fractions and low Reynolds number, particle-laden turbulence at high Reynolds and moderate volume fraction and particulate regime at high volume fractions. We show that in the viscous dominated regime, the heat transfer is mainly due to thermal diffusion with enhancement due to the particle-induced fluctuations. In the turbulent-like regime, we observe the largest enhancement of the global heat transfer, dominated by the turbulent heat flux. In the particulate shear-thickening regime, however, the heat transfer enhancement decreases as mixing is quenched by the particle migration towards the channel core. As a result, a compact loosely-packed core region forms and the contribution of thermal diffusion to the total heat transfer becomes significant once again. The global heat transfer becomes, in these flows at volume fractions larger than 25%, lower than in single phase turbulence. [ABSTRACT FROM AUTHOR]

• We study rigid particle suspensions in a Couette flow with porous walls. • The porous walls induce a decrease in the suspension effective viscosity. • The presence of porous walls weakens the wall blocking effect. • We provide a closed set of equations for the suspension viscosity. We study the effect of isotropic porous walls on a plane Couette flow laden with spherical and rigid particles. We perform a parametric study varying the volume fraction between 0 and 30 % , the porosity between 0.3 and 0.9 and the non-dimensional permeability between 0 and 7.9 × 10 - 3 We find that the porous walls induce a progressive decrease in the suspension effective viscosity as the wall permeability increases. This behavior is explained by the weakening of the wall-blocking effect and by the appearance of a slip velocity at the interface of the porous medium, which reduces the shear rate in the channel. Therefore, particle rotation and the consequent velocity fluctuations in the two phases are dampened, leading to reduced particle interactions and particle stresses. Based on our numerical evidence, we provide a closed set of equations for the suspension viscosity, which can be used to estimate the suspension rheology in the presence of porous walls. [ABSTRACT FROM AUTHOR]