Suspension Of Particles In Liquid Research Articles

Dynamics analysis of cavitation disintegration of microparticles during nanopowder preparation in a new Water Jet Mill (WJM) device

A physical analysis of cavitation-based implosive breakage of solid particles focusing on practical application during fine particle disintegration in a liquid suspension is submitted in the present paper. The physical source of the cavitation dynamics phenomena involved is an extreme velocity gradient induced by an ultrahigh-energy liquid jet mixing together with a slow liquid suspension of milled particles. Extreme tensile stresses occurring at velocity gradients over 1000 ms −1mm −1 at the operating temperature of 65 °C generates high-intensity pure vapor cavitation in the degassed water dispersion with extreme values of impact pressure in the final of bubble implosions on particle surfaces. Preparation of silicon nanoparticles with median diameter approximately 148 nm using a newly developed “Water Jet Mill” (WJM) device is demonstrated in the present article as an example of application of the aforementioned disintegration method as well as of theoretical analysis of this method. The disintegration method is characterized by a high potential for milling of submicron particles with high efficiency.

Practical screening of purified cellobiohydrolases and endoglucanases with α-cellulose and specification of hydrodynamics

BackgroundIt is important to generate biofuels and society must be weaned from its dependency on fossil fuels. In order to produce biofuels, lignocellulose is pretreated and the resulting cellulose is hydrolyzed by cellulases such as cellobiohydrolases (CBH) and endoglucanases (EG). Until now, the biofuel industry has usually applied impractical celluloses to screen for cellulases capable of degrading naturally occurring, insoluble cellulose. This study investigates how these cellulases adsorb and hydrolyze insoluble α-cellulose − considered to be a more practical substrate which mimics the alkaline-pretreated biomass used in biorefineries. Moreover, this study investigates how hydrodynamics affects cellulase adsorption and activity onto α-cellulose.ResultsFirst, the cellulases CBH I, CBH II, EG I and EG II were purified from Trichoderma reesei and CBH I and EG I were utilized in order to study and model the adsorption isotherms (Langmuir) and kinetics (pseudo-first-order). Second, the adsorption kinetics and cellulase activities were studied under different hydrodynamic conditions, including liquid mixing and particle suspension. Third, in order to compare α-cellulose with three typically used celluloses, the exact cellulase activities towards all four substrates were measured.It was found that, using α-cellulose, the adsorption models fitted to the experimental data and yielded parameters comparable to those for filter paper. Moreover, it was determined that higher shaking frequencies clearly improved the adsorption of cellulases onto α-cellulose and thus bolstered their activity. Complete suspension of α-cellulose particles was the optimal operating condition in order to ensure efficient cellulase adsorption and activity. Finally, all four purified cellulases displayed comparable activities only on insoluble α-cellulose.Conclusionsα-Cellulose is an excellent substrate to screen for CBHs and EGs. This current investigation shows in detail, for the first time, the adsorption of purified cellulases onto α-cellulose, the effect of hydrodynamics on cellulase adsorption and the correlation between the adsorption and the activity of cellulases at different hydrodynamic conditions. Complete suspension of the substrate has to be ensured in order to optimize the cellulase attack. In the future, screenings should be conducted with α-cellulose so that proper cellulases are selected to best hydrolyze the real alkaline-pretreated biomass used in biorefineries.

Deformation and friction of MoS 2 particles in liquid suspensions used to lubricate sliding contact

Tribology of a well known solid lubricant molybdenum disulphide is studied here in water and oil medium, over a large range of contact dimensions. Lateral force microscopy is used to identify the deformation modes; intra-crystalline slip, plastic grooving, fragmentation and fracture, of single particles. The medium and agglomeration were found to dictate the deformation mode. Steel on steel tribology lubricated by suspensions of these particles in liquid media was conducted over a range of contact pressure and sliding velocity. A scrutiny of the frictional data with the aid of Raman spectroscopy to identify the transfer film, suggested that the particle size, as it is at contact, is an important tribological parameter. Ultrasonication of the suspension and dispersion of the particle by surfactants were used to control the apriori particle size fed into the suspension. Correspondence of friction data of the gently sonicated suspension with that of the ultrasonicated suspension with dispersants indicated the importance of liquid ingestion by these particles as it controls their mode of deformation and consequent tribology.

Viscoelasticity-induced migration of a rigid sphere in confined shear flow

Suspensions of solid particles in liquids are often made to flow in devices with characteristic dimensions comparable to that of the suspended particles, the so-called confined situation, as in the case of several microfluidic applications. Combination of confinement with viscoelasticity of the suspending liquid can lead to peculiar effects. In this paper we present the first 3D simulation of the dynamics of a particle suspended in a viscoelastic liquid under imposed confined shear flow. The full system of equations is solved through the finite element method. A DEVSS/SUPG formulation with a log-representation of the conformation tensor is implemented, assuring stable and convergent results up to high flow rates. Particle motion is handled through an ALE formulation. To optimize the computational effort and to reduce the remeshing and projection steps required when the mesh becomes too distorted, a rigid motion of the grid in the flow direction is performed, so that, in fact, the particle moves along the cross-streamline direction only. Confinement and viscoelasticity are found to induce particle migration, i.e., transverse motion across the main flow direction, towards the closest wall. Under continuous shearing, three different dynamical regimes are recognized, related to the particle-wall distance. A simple heuristic argument is given to link the cross-flow migration to normal stresses in the suspending liquid. The analysis is then extended to a time-dependent shear flow imposed by periodically inverting the direction of wall motion. A slower migration is found for higher forcing frequency. A peculiar effect arises if the inversion period is chosen close to the fluid relaxation time: the migration velocity oscillates around zero, and the overall migration is suppressed. Such novel prediction of a dynamic instability scenario, with the particle escaping the center plane of the channel, and many features of the computed results, are in nice agreement with recent experiments reported in the literature [14].

Porous Architecture of SPS Thick YSZ Coatings Structured at the Nanometer Scale (~50 nm)

Suspension plasma spraying (SPS) is a fairly recent technology that is able to process sub-micrometer-sized or nanometer-sized feedstock particles and permits the deposition of coatings thinner (from 20 to 100 μm) than those resulting from conventional atmospheric plasma spraying (APS). SPS consists of mechanically injecting within the plasma flow a liquid suspension of particles of average diameter varying between 0.02 and 1 μm. Due to the large volume fraction of the internal interfaces and reduced size of stacking defects, thick nanometer- or sub-micrometer-sized coatings exhibit better properties than conventional micrometer-sized ones (e.g., higher coefficients of thermal expansion, lower thermal diffusivity, higher hardness and toughness, better wear resistance, among other coating characteristics and functional properties). They could hence offer pertinent solutions to numerous emerging applications, particularly for energy production, energy saving, etc. Coatings structured at the nanometer scale exhibit nanometer-sized voids. Depending upon the selection of operating parameters, among which plasma power parameters (operating mode, enthalpy, spray distance, etc.), suspension properties (particle size distribution, powder mass percentage, viscosity, etc.), and substrate characteristics (topology, temperature, etc.), different coating architectures can be manufactured, from dense to porous layers, from connected to non-connected network. Nevertheless, the discrimination of porosity in different classes of criteria such as size, shape, orientation, specific surface area, etc., is essential to describe the coating architecture. Moreover, the primary steps of the coating manufacturing process affect significantly the coating porous architecture. These steps need to be further understood. Different types of imaging experiments were performed to understand, describe and quantify the pore level of thick finely structured ceramics coatings.

Surprising Particle Stability and Rapid Sedimentation Rates in an Ionic Liquid

In this letter we demonstrate that particle suspensions in room temperature ionic liquids differ from aqueous suspensions in some surprising and remarkable ways. Two results are of key importance. First, suspensions of 1 μm diameter silica spheres do not aggregate in pure ethylammonium nitrate (EAN) despite interparticle electrostatic repulsions being completely screened by its 11 M ionic strength. However these dispersions become unstable in the presence of small amounts of water. Using silica colloid probe atomic force microscopy (AFM), optical microscopy and dynamic light scattering we show that this unusual stability is imparted by repulsions between well formed solvation layers, which decrease in number and strength upon addition of water. Second, particle suspensions in pure EAN settle six times more rapidly than predicted by the hindered Stokes equation. This remarkable result is unprecedented in the literature to our knowledge, and could foreshadow interesting lubrication effects for surfaces in EAN.

Dynamic magnetic hysteresis in a liquid suspension of acicular maghemite particles

This paper presents theoretical and experimental studies on the magnetodynamics and energy absorption in a dilute suspension of small ferromagnetic particles with magnetic hysteresis and mechanical mobility in an AC magnetic field. Experiments with 0.1% suspensions of acicular particles of gamma ferric oxide in solid and liquid matrices, subjected to a 430 Hz magnetic field with an intensity of up to 1200 Oe, revealed important role of particle mobility. The main qualitative and quantitative features of the phenomenon are in agreement with a model of joint magneto-mechanical dynamics of particles with a chain-of-spheres mode of incoherent magnetic reversal.

Foamability of Liquid Particle Suspensions: A Modeling Study

Recent experiments on the foamability of liquid particle suspensions (with a particle size varying from nanometers to micrometers in diameter and in the absence of any surfactants) have shown that the foamability correlates well with the degree of particle coverage at the air−liquid surface. Furthermore, these experiments have also revealed foam inhibition due to the aggregation or clustering of particles in the bulk at high particle concentrations. The present study is aimed at theoretically modeling the observed phenomena. Theoretical analyses based on Monte Carlo simulations and the integral equations of statistical mechanics are used to model the particle aggregation phenomena in the bulk. The radial distribution functions, which show the particle packing density, are analyzed to obtain the effective energy of interaction between the particles. The maximum in foaminess due to the adsorption of particles on the air−liquid surface and clustering of particles in the bulk is explained. The modeling result...

Non-Equilibrium Magnetization of a Dilute Suspension of Magnetic Particles

A suspension of magnetic particles in a viscous liquid magnetized in an alternating uniform magnetic field is theoretically studied. The suspension is regarded as so dilute that interaction of a single particle with the applied magnetic field can be considered without taking into account the influence of other particles. The complex magnetic susceptibility of the suspension is found as a function of the frequency of the applied magnetic field. The heat generation power density averaged over the period of the oscillations is calculated.

Positron emission particle tracking in a mechanically agitated solid–liquid suspension of coarse particles

The technique of positron emission particle tracking (PEPT) is a unique non-intrusive Lagrangian flow visualisation technique which allows probing of opaque fluids and within opaque apparatus. It uses a single positron-emitting particle as flow tracer which is tracked in 3D space and time to reveal its full Lagrangian trajectory. PEPT was used to study the mixing of a concentrated suspension of coarse glass particles, containing up to 10.6 wt% solids, in a vessel agitated by a pitched blade turbine operating in both up-pumping and down-pumping modes. The Lagrangian information obtained was used to obtain a detailed Eulerian description of the two-phase flow inside the vessel. For the first time, it has been possible to determine the full 3D velocity and concentration fields of both the liquid and the solid phase within an opaque flow of this type.

A review on nanofluids - part I: theoretical and numerical investigations

Research in convective heat transfer using suspensions of nanometer-sized solid particles in base liquids started only over the past decade. Recent investigations on nanofluids, as such suspensions are often called, indicate that the suspended nanoparticles markedly change the transport properties and heat transfer characteristics of the suspension. This first part of the review summarizes recent research on theoretical and numerical investigations of various thermal properties and applications of nanofluids.

A review on nanofluids - part II: experiments and applications

Research in convective heat transfer using suspensions of nanometer-sized solid particles in base liquids started only over the past decade. Recent investigations on nanofluids, as such suspensions are often called, indicate that the suspended nanoparticles markedly change the transport properties and heat transfer characteristics of the suspension. This second part of the review covers fluid flow and heat transfer characteristics of nanofluids in forced and free convection flows and potential applications of nanofluids. Opportunities for future research are identified as well. Keywords: Nanofluids; Nanoparticles; Heat transfer; Thermal conductivity.

Suspension Plasma-Sprayed Alumina Coating Structures: Operating Parameters Versus Coating Architecture

Suspension plasma spraying (SPS) is able to process sub-micrometric-sized feedstock particles and permits the deposition of layers thinner (from 5 to 50 μm) than those resulting from conventional atmospheric plasma spraying (APS). SPS consists in mechanically injecting within the plasma flow a liquid suspension of particles of average diameter varying between 0.02 and 1 μm, average values. Upon penetration within the DC plasma jet, two phenomena occur sequentially: droplet fragmentation and evaporation. Particles are then processed by the plasma flow prior their impact, spreading and solidification upon the surface to be covered. Depending upon the selection of operating parameters, among which plasma power parameters (operating mode, enthalpy, spray distance, etc.), suspension properties (particle size distribution, powder mass percentage, viscosity, etc.), and substrate characteristics (topology, temperature, etc.), different coating architectures can be manufactured, from dense to porous layers. Nevertheless, the coupling between the parameters controlling the coating microstructure and properties are not yet fully identified. The aim of this study is to further understand the influence of parameters controlling the manufacturing mechanisms of SPS alumina coatings, particularly the spray beads influence.

Multipolar Contributions of the Second Harmonic Generation from Silver and Gold Nanoparticles

Hyper Rayleigh scattering is used to investigate the second harmonic light collected from a liquid suspension of silver metallic particles, the diameter of which ranges from 20 nm up to 80 nm. From the dependence of the quadratic hyperpolarizability as a function of the particle size, it is inferred that retardation effects of the electromagnetic fields play a major role in the frequency conversion process. The hyper Rayleigh scattering intensity was also recorded as a function of the angle of polarization of the incident fundamental wave. For the particles with a diameter of 20 nm, the harmonic response is dominated by the dipolar contribution arising from the deviation of the particle shape from that of a perfect sphere. It is therefore concluded that the origin of the nonlinear polarization for the smaller silver particle sizes arises from the surface similarly to the case of the gold metallic particles. For larger diameter particles, retardation effects in the interaction of the electromagnetic fields...

Discrete element simulation of liquid-particle flows

A deterministic model for predicting the flow of suspensions of particles in viscous liquids is presented. The discrete element method (DEM) is used for evaluating the motion of the suspended particles by accounting the forces acting on them. Particle–particle and particle–wall colloidal, hydrodynamic and soft-sphere collision forces and Stokes-like drag from the suspending medium are considered. The flow of the suspending medium, assumed unaffected by the presence of the particles, is evaluated by a Finite Element Method. The model is applied to flow of a suspension of sub-micro-sized particles inside a three-dimensional geometry that resembles the exit of a slot coater. Because of the large number of particles involved, parallelization of the algorithm is necessary. The preliminary results indicate the effect of the accounted forces on the agglomeration process. The parallelization speed-up is excellent.

Reproducible cavitation activity in water-particle suspensions

The study of cavitation inception in liquids rarely yields reproducible data, unless special control is taken on the cleanliness of the experimental environment. In this paper, an experimental technique is demonstrated which allows repeatable measurements of cavitation activity in liquid-particle suspensions. In addition, the method is noninvasive: cavitation bubbles are generated using a shock-wave generator, and they are photographed using a digital camera. The cavitation activity is obtained after suitable image processing steps. From these measurements, the importance of the particle's surface structure and its chemical composition is revealed, with polystyrene and polyamide particles generating the highest yields. Further findings are that cavitation nuclei become depleted with an increasing number of experiments, and the existence of nuclei with varying negative pressure thresholds. Finally, a decrease of the cavitation yield is achieved by prepressurization of the suspension-indicating that the cavitation nuclei are gaseous.

Refrigeration aspects of magnetic particle suspensions

This study examines the feasibility of using magnetic particles in liquid suspension as a working fluid to achieve room temperature refrigeration with a permanent magnetic field source. Potential advantages include facilitation of regenerative heat transfer while avoiding wear, drag, and leakage problems of mechanical sliding seals associated with the use of a solid magnetic working substance. Rheological properties are evaluated in defining an appropriate composition, and performance estimates developed for a conceptual embodiment.

Publisher’s Note: Strain hardening in liquid-particle suspensions [Phys. Rev. E72, 061402 (2005)

Publisher’s Note: Strain hardening in liquid-particle suspensions [Phys. Rev. E<b>72</b>, 061402 (2005)

Strain hardening in liquid-particle suspensions

The behavior of a liquid-particle suspension induced to sheared motion was analyzed by numerical simulations. When the velocity (strain) of the suspension began to increase, its viscosity first stayed almost constant, but increased then rapidly to a clearly higher level. This increase in viscosity is shown to be related to formation of clusters of suspended particles. Clusters are shown to increase the viscosity by enhanced momentum transfer though clustered particles. This is the mechanism behind the strain-hardening phenomenon observed in small-strain experiments on liquid-particle suspensions.

Ultrasonic wave propagation in particulate mixtures

Measurements of ultrasonic compression wave attenuation as a function of frequency can provide a means to monitor suspensions of microscopic particles in liquids on-line in a process setting. Such mixtures are important in many industrial sectors including chemical, mineral, pharmaceutical, agrochemical and food. The ultrasonic data can be used to estimate the dispersed phase particle size distribution and to quantify dynamic effects such as flocculation and crystallization. The technique requires a detailed mathematical model to relate the ultrasonic wavenumber to mixture properties, and there are two distinct approaches to this—scattering and hydrodynamic. Although both have been shown to adequately describe sound propagation in dilute mixtures (up to ∼5% v/v), current models fail for concentrated suspensions of high density particles. The applicability of existing and future models of wave propagation in these suspensions will be greatly improved with more rigorous formulations for the local viscosity in the vicinity of a suspended particle, viscosity being the principal loss mechanism in such mixtures. In this paper five different theoretical formulations for local viscosity are investigated; their effects on wavenumber when included in both scattering and hydrodynamic propagation theories are compared, with reference to experimental data.