Suspension Of Small Particles Research Articles

The importance of transparent exopolymer particles over ballast in determining both sinking and suspension of small particles during late summer in the Northeast Pacific Ocean

Gravitational sinking of particles is a key pathway for the transport of particulate organic carbon (POC) to the deep ocean. Particle size and composition influence particle sinking velocity and thus play a critical role in controlling particle flux. Canonically, sinking particles that reach the mesopelagic are expected to be either large or ballasted by minerals. However, the presence of transparent exopolymer particles (TEP), which are positively buoyant, may also influence particle sinking velocity. We investigated the relationship between particle composition and sinking velocity during the Export Processes in the Ocean from RemoTe Sensing (EXPORTS) campaign in the Northeast Pacific Ocean using Marine Snow Catchers. Suspended and sinking particles were sized using FlowCam for particle imaging, and their biogeochemical composition was assessed by measuring the concentration of particulate organic carbon (POC) and nitrogen, particulate inorganic carbon, biogenic and lithogenic silica, and TEP. Sinking fluxes were also calculated. Overall, both suspended and sinking particles were small (<51 μm, diameter) in this late summer, oligotrophic system. Contrary to expectation, the ratio of ballast minerals to POC was higher for suspended particles than sinking particles. Further, suspended particles showed TEP-to-POC ratios three times higher than sinking particles. These ratios suggest that TEP content and not ballast dictated whether particles in this system would sink (low TEP) or remain suspended (high TEP). Fluxes of POC averaged 4.3 ± 2.5 mmol C m−2 d−1 at 50 m (n = 9) and decreased to 3.1 ± 1.1 mmol C m−2 d−1 at 300–500 m (n = 6). These flux estimates were slightly higher than fluxes measured during EXPORTS with drifting sediment traps and Thorium-234. A comparison between these approaches illustrates that small sinking particles were an important component of the POC flux in the mesopelagic of this late summer oligotrophic system.

Experimental Measurement of Enhanced and Hindered Particle Settling in Turbulent Gas‐Particle Suspensions, and Geophysical Implications

AbstractThe dynamics of geophysical dilute turbulent gas‐particles mixtures depends to a large extent on particle concentration, which in turn depends predominantly on the particle settling velocity. We experimentally investigate air‐particle mixtures contained in a vertical pipe in which the velocity of an ascending air flux matches the settling velocity of glass particles. To obtain local particle concentrations in these mixtures, we use acoustic probing and air pressure measurements and show that these independent techniques yield similar results for a range of particle sizes and particle concentrations. Moreover, we find that in suspensions of small particles (78 μm) the settling velocity increases with the local particle concentration due to the formation of particle clusters. These clusters settle with a velocity that is four times faster than the terminal settling velocity of single particles, and they double settling speeds of the suspensions. In contrast, in suspensions of larger particles (467 μm) the settling velocity decreases with increasing particle concentration. Although particle clusters are still present in this case, the settling velocity is decreased by 30%, which is captured by a hindered settling model. These results suggest an interplay between hindered settling and cluster‐induced enhanced settling, which in our experiments occur respectively at Stokes number O(100) and O(1). We discuss implications for volcanic plumes and pyroclastic currents. Our study suggests that clustering and related enhanced or hindered particle settling velocities should be considered in models of volcanic phenomena and that drag law corrections are needed for reliable predictions and hazard assessment.

Editorial for the Special Issue on Advances in Microfluidics for Quantifying Cell Mechanics and Biotransport

Microfluidics is a powerful tool to precisely control fluids as well as to manipulate suspended small particles in a micrometer-sized space [...].

Lubrication theory and boundary element hybrid method for calculating hydrodynamic forces between particles in near contact

Suspensions of small particles are ubiquitous; examples include aqueous dispersions of solid particles, vesicles, capsules, cells, swimming microorganisms and artificial microswimmers. The rheological and diffusion properties of small particle suspensions are strongly influenced by near-field interactions between particles. Lubrication theory (LT) is a classical analytical technique used to obtain asymptotic solutions of forces and torques acting in the lubrication region. The boundary element method (BEM), on the other hand, is a computational method for accurately calculating Stokes flow around particles. To dramatically improve the near-field accuracy of the BEM, a novel hybrid method combining LT and BEM (LT-BEM) is proposed in this study, in which the inner solution is obtained by LT, whereas the outer solution is obtained by BEM. The validity of the LT-BEM was confirmed based on the shearing, rotational, and squeezing motions of two spheres. The asymptotic nature of the forces and torques exerted on the two spheres were efficiently captured by the LT-BEM. Especially, the squeezing force of the BEM was improved dramatically by the LT-BEM, which is important to prevent particle overlap. The obtained results can be expanded to the arbitrary motions of many spheres without loss of generality. Moreover, the LT-BEM can accommodate particles with arbitrary shapes. The advantages of the LT-BEM are demonstrated for two kinds of applications; (i) dynamic interactions of pairwise microswimmers with surface velocities, and (ii) pairwise interactions of bacteria. The obtained knowledge should be useful for computing various suspensions of small particles in nature and industrial applications.

Non-uniform pumping flow model for the couple stress particle-fluid under magnetic effects

In this article, peristaltically induced motion of couple stress fluid under the suspension of small particles have been studied. A peristaltic wave with non-uniform motion is traveling with a constant wave celerity. An extrinsic magnetic field is applied to an electrically conducting incompressible fluid with irrotational motion. Lubrication theory is applied for the mathematical formulation of both fluid- and particle-phase equations. Analytically and numerically, the formulated equations are solved using computational software Mathematica. The exact solutions are determined against the velocity profile for both fluid- and particulate-phases. The volumetric flow rate is also presented and calculated numerically to examine the pumping characteristics. Trapping mechanisms via streamlines are plotted and discussed against all the leading parameters. The present results are also beneficial to observe the Newtonian behavior and single phase fluid model. It is also observed that magnetic field opposes the fluid movement in the middle of the channel, while the presence of small particles tends to resist the fluid motion along the whole channel. A significant reduction in the pumping rate was observed due to the rise in the couple stress fluid parameter, the fraction of the particle volume, and the average volume flow rate, but a dual behavior is observed against the magnetic parameter. The fluid bolus diminishes in magnitude and reduces in quantity against the higher values of Hartmann number.

Counterion Phenomena Near Charged Surfaces in Finite Volumes

Lipid-membrane headgroups are invariably charged or zwitterionic. The headgroups can be weak acids (negatively charged when deprotonated), weak bases (positively charged when protonated), or zwitterionic (both types of groups present). Headgroups can also be salts, such as TMA+Cl- in the lipid DOTAP+. The screening of surface charge by dissociated counterions is usually negligible, as dissociated counterions are normally diluted to concentrations far below that of the ambient salt. However for a suspension of charged particles in a finite volume, the mean concentration of dissociated counterions depends on the suspension's surface charge/volume ratio, which for moderately concentrated suspensions of small particles can be quite high. Significant concentrations of dissociated counterions can screen and uncouple electrostatic interactions between like-charged particles. Such effects are readily observed in deionized suspensions where background salt is of order 10−7 M. However in the presence of high salt, surface-dissociated counterions get masked by the salt counterions. Here we determine the maximum background salt concentrations at which dissociated-counterion screening can occur. For example, for 100 nm liposomes containing 20 mol% cationic or weak-acid lipids at 0.1 volume-fraction liposome concentration, dissociated counterions can reach mean concentrations of order 10 mM, or if the counterions are protons, mean pH∼2. Although charge regulation can in some cases reduce the number of dissociated counterions, dissociated-counterion phenomena, i.e. screening-ion numbers proportional to total surface charge, can occur in the presence of surprisingly high values of ambient salt or acid.

Evaluating the erosion resistance of Ti6Al4V coatings deposited by cold spray

Ti6Al4V alloys are widely used in components of the aeronautical industry. Consequently, impact erosion with small particles in suspension has revealed to be one of the most common damage processes during its service life. In order to study the possibility of repairing these components by spraying coatings, in this work, the behavior against erosion by the impact of abrasive particles of Ti6Al4V coatings manufactured by cold spray has been analyzed. The work includes the comparison between the responses of the coating and the bulk alloy, analyzing the effect of the speed and the angle of impact of the erosive particles on the erosion rate. The values of the spraying parameters used in this work have allowed obtaining coatings that showed a behavior against erosion similar to that of the bulk material. It has been possible to identify a ductile behavior of the coating and alloy dominated by plastic deformation. Through the study of erosion scars, two damage processes, microploughing and microcutting, have been identified as the dominant mechanisms responsible for the erosion process.

Mean field surrogate model of a dilute and chaotic particle suspension

AbstractWe present a mean field approximation for a dilute suspension of small particles, which accounts for a non‐homogeneous particle distribution and small inertial effects of the particle phase. The model consists of the momentum equation for the fluid coupled to a transport equation for the probability density function on the particle phase space. Apart from the well‐known particle extra stress tensor first presented by Batchelor (1970), the fluid equation contains additional force terms resulting from inertia and hydrodynamic interaction of the particles. A brief sketch of the main derivation steps is presented.

Effects of mine tailings exposure on early life stages of atlantic cod.

In Norway, mine tailings waste can be deposited by coastal submarine dispersal. Mine tailings slurry includes fine particles <10 µm with elevated levels of metals (e.g., copper, iron) from residual mineral ore. Prolonged suspension of small particles in the water column may bring them into contact with locally spawned pelagic fish eggs, including Atlantic cod, Gadus morhua. Newly fertilized cod embryos were exposed to suspended mine tailings particles up to 3.2 mg/L in flow‐through aquaria for a total of 21 d. Significantly more particles adhered to the surface of the chorion from the high treatment after 11‐d exposure, and dissolved Cu concentrations increased in the water (up to 0.36 ± 0.06 µg/L). There was no adverse effect on embryo mortality but an 8% elevation in larval mortality. There were no differences with treatment on timing of hatching, embryo and larva morphometrics, abnormalities, or cardiac activity. There was a treatment‐dependent up‐regulation of stress marker genes (hspa8, cyp1c1) but no indication of metal‐induced activation of metallothionien (mt gene transcription). Transcription markers for DNA and histone methyltransferases did show treatment‐related up‐regulation, indicative of altered methylation in larvae when developmental methylation patterns are determined, indicating some level of chronic toxicity that may have longer‐term effects. Environ Toxicol Chem 2019;38:1446–1454. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Determination of particle distributions from sedimentation measurements using a piezoelectric tuning fork sensor

In this work, a resonant quartz tuning fork sensor based measurement system is employed to study the settlement of small particles in suspension as they pass the sensing element. The resonator features varying sensitivity to fluid parameter changes along its length, with the tip being most sensitive. The spatial averaging effect is analyzed theoretically and measured by passing the sensor through a fluid–fluid interface. Subsequently, the averaging function is used for particle distribution determination from recorded resonance frequency and quality factor measurements. The associated inverse problem is of Fredholm type and is solved numerically. Based on the system specifications, detection limits, required temperature stability and expected precision are assessed and particle distribution functions of defined test dispersions are measured.

Preparation of flocculant for optimizing glycol lignin manufacturing process by cationization of glycol lignin

Glycol lignin possessing thermoplastic and fusible properties can be a biorefinery platform material; however, glycol lignin is obtained as very small particles in suspension and the low dewatering efficiency is a major difficulty for the mass production. To improve the productivity of glycol lignin in the refinery plant, glycol lignin-based flocculants were prepared and their flocculation performance was examined. The flocculants (cationized glycol lignins) were synthesized by a reaction with glycidyltrimethylammonium chloride (GTA) in various reaction conditions. The prepared flocculants exhibited high flocculation performance and successfully economized the production cost of glycol lignin. Their flocculation efficiency was affected by the precipitation temperature, the length of the glycol chain, the molecular weight and the functional group of the glycol lignin. The flocculation behavior was interpreted by phase separation theory at a lower critical solution temperature (LCST).

“Structural characterization of protein isolates obtained from chia (Salvia hispanica L.) seeds”

Chia protein isolates (CPI) were obtained through isoelectric precipitation under two different conditions in order to compare their structural properties. Extraction was carried out at pH 10 or 12, whereas precipitation pH was fixed at 4.5. Samples were named as CPI10 or CPI12, according to their extraction pH (10 or 12, respectively). The recovery of chia proteins was higher when the extraction was carried out at pH 12 (17% for CPI12 and 13% for CPI10); however, CPI12 protein content (775 g/kg) was slightly lower than CPI10 protein content (782 g/kg). Both samples showed similar SDS-PAGE pattern. Protein dispersions of both isolates led to highly stabilized particles due to their negative ζ potential (around −54 mV). CPI10 has a higher proportion of small particles in suspension, revealed by a lower d3,2 value. Spectroscopic techniques showed that CPI10 presented higher content of β-helix than CPI12, resulting in higher thermal stability. This observation was supported by FT-IR spectroscopy since CPI10 presented less unordered structure than CPI12. The energy of endotherms obtained in CPI12 was considerably lower than in CPI10. Extraction at higher alkaline conditions led to a more denatured protein conformation with a higher content of random structure (18.1% for CPI10 and 22.9% for CPI12).

Deviation-angle and trajectory statistics for inertial particles in turbulence.

Small particles in suspension in a turbulent fluid have trajectories that do not follow the pathlines of the flow exactly. We investigate the statistics of the angle of deviation ϕ between the particle and fluid velocities. We show that, when the effects of particle inertia are small, the probability distribution function (PDF) P_{ϕ} of this deviation angle shows a power-law region in which P_{ϕ}∼ϕ^{-4}. We also find that the PDFs of the trajectory curvature κ and modulus θ of the torsion ϑ have power-law tails that scale, respectively, as P_{κ}∼κ^{-5/2}, as κ→∞, and P_{θ}∼θ^{-3}, as θ→∞: These exponents are in agreement with those previously observed for fluid pathlines. We propose a way to measure the complexity of heavy-particle trajectories by the number N_{I}(t,St) of points (up until time t) at which the torsion changes sign. We present numerical evidence that n_{I}(St)≡lim_{t→∞}N_{I}(t,St)/t∼St^{-Δ} for large St, with Δ≃0.5.

Sensitive Detection of Small Particles in Fluids Using Optical Fiber Tip with Dielectrophoresis.

This work presents using a tapered fiber tip coated with thin metallic film to detect small particles in water with high sensitivity. When an AC voltage applied to the Ti/Al coated fiber tip and indium tin oxide (ITO) substrate, a gradient electric field at the fiber tip induced attractive/repulsive force to suspended small particles due to the frequency-dependent dielectrophoresis (DEP) effect. Such DEP force greatly enhanced the concentration of the small particles near the tip. The increase of the local concentration also increased the scattering of surface plasmon wave near the fiber tip. Combined both DEP effect and scattering optical near-field, we show the detection limit of the concentration for 1.36 μm polystyrene beads can be down to 1 particle/mL. The detection limit of the Escherichia coli (E. coli) bacteria was 20 CFU/mL. The fiber tip sensor takes advantages of ultrasmall volume, label-free and simple detection system.

Delaying Boundary Layer Separation in a Retarded Potential Flow

The phenomena of convective transport in the boundary layer flow carrying a dilute nanosize suspension of small particles past a stationary wedge is investigated in this communication. The nanofluid modeling is based on non-homogeneous nanoparticle concentration within the boundary layer along with variable thermophysical material properties. It is shown that for the present nanofluid modelling the self-similar solution also exists as it does for the pure fluid case. The self-similar solution is found to exist for the situation when the undisturbed potential flow is of the form \(u_e \left( x \right) =u_1 x^{m}\). A number of qualitatively distinct potential scenarios are predicted concerning the physics of flow and heat transfer. These include boundary layer separation; control or its delay, and heat transfer enhancement. In depth analysis of momentum transport across the boundary layer revealed interesting physics. Worth mentioning effect of nanoparticle is to (slightly) delay the boundary layer separation in the case of retarding potential flow. The values of m are calculated for which the separation starts and are found to depend upon the nanoparticle concentration. Heat transfer augmentation connected directly with the nanoparticle concentration is also an important conclusion of this study.

Experimental Test of Reflectivity Formulas for Turbid Colloids: Beyond the Fresnel Reflection Amplitudes.

We compare light reflectivity measurements as a function of the angle of incidence for an interface between an optical glass and a turbid suspension of small particles, with theoretical predictions for the coherent reflectance calculated with different available theoretical models. The comparisons are made only in a small range of angles of incidence around the critical angle of the interface between the glass and the matrix of the colloidal suspensions. The experimental setup and its calibration procedure are discussed. We considered two Fresnel-based approximations and another two based on a multiple-scattering approach, and we present results for monodisperse latex colloidal suspensions of polymeric spherical particles in water with particle diameters of 120 and 520 nm, polydisperse titanium dioxide (rutile) particles suspensions in water with a most probable diameter of 404 nm, and suspensions of copper particles in water with diameters of 500 nm. The comparisons between experiment and theory are made without fitting any parameters.

Comparison of solids suspension criteria based on electrical impedance tomography and visual measurements

Different approaches have been adopted to quantify the performance of stirred vessels in suspending sinking solids into liquid phase. In this study we used electrical impedance tomography (EIT) to estimate the solids distribution in a lab-scale stirred vessel with a diameter of 362mm. Also visual measurements were performed to determine the cloud height and just suspended impeller speed. Quartz sand with a density of 2650kg/m3 was employed as the solid phase with different particle size fractions from 50 to 180µm and solids volume fractions of 7.5% and 15%. The effect of impeller type was studied by using two axial flow impellers, a pitched blade turbine and a hydrofoil impeller.Two different states—partial and homogeneous suspensions—were defined from the EIT data in addition to visual measurement of complete off-bottom suspension and cloud height. Partial suspension was determined from the EIT data, and it was reached at relatively low agitation rates. Visual measurements and data from the literature also support this observation, and EIT was proved to be a suitable method to quantify a repeatable partial suspension criterion. Complete off-bottom suspension was measured visually by determining the agitation rate at which there were no stationary solid particles at the vessel bottom for longer than 2s. However, the applicability of this widely used criterion was questioned in the case of dense suspensions of small particles. Homogeneous suspension was estimated from the EIT data, and it was reached by approximately doubling the impeller revolution rate from the partial suspension criterion. The hydrofoil impeller reached all states of suspension with lower power consumption compared to the pitched blade turbine.

Treatment of water networks (waters and deposits) contaminated with chlorfenvinphos by oxidation with Fenton’s reagent

The treatment of waters/deposits from drinking water networks contaminated with chlorfenvinphos (CFVP) was performed through the Fenton’s process. Concerning the CFVP degradation in water matrices, the mineralization and CFVP concentration in a batch reactor were analysed along time for several operating conditions. A detailed parametric study was done to analyse the effect of the initial concentrations of oxidant (H2O2) and catalyst (Fe2+), temperature and initial pH, allowing concluding that temperature significantly affects the degradation process. In fact, in the range from 10 to 70°C, the time for complete degradation of CFVP decreased from 3h to only 5min. In the same temperature range, the mineralization after 3h increased from 5% to 35%. The effect of other parameters is not so significant; depending on their values they can affect positively or negatively the responses.The degradation of the pesticide was assessed for the first time using deposits from water networks as catalysts. These deposits result from the natural deposition of small particles in suspension, being in some cases highly rich in iron, and therefore it is envisaged the valorisation of these materials for off-line applications and the possibility of avoiding the use of some reagents –catalyst – if an in situ treatment is required.The decontamination of deposits was assessed in a slurry batch system, showing to be possible to use iron-rich deposits as catalysts in the oxidation process, as well as to decontaminate them using as catalyst the iron present in their composition. Results showed that oxidation is fast and effective in the liquid phase (conversion >95% in 1h); the pesticide was also removed from the solid, although apparently not always in a complete manner, in the conditions tested.

Lift-Off Behavior of Micro and Nanoparticles in Contact With a Flat Surface

The suspension of small particles from flat surfaces is recognized as a source of pollution and a potential hazard to exposed humans. The interaction of air flow over a particle in contact with a flat surface was studied. Parameters that affect the air flow-particle-surface interaction were taken into consideration and conditions that would lead to particle lift-off were identified. The results showed that particles 100 nm in size will lift-off from the surface for separation distances greater than 20 nm. A mapping strategy is proposed that could be used to minimize the suspension of small particles if the particle size and separation distances are known.

Convexity-preserving flux identification for scalar conservation laws modelling sedimentation

Sedimentation of a suspension of small particles dispersed in a viscous fluid can be described by a scalar, nonlinear conservation law, whose flux function usually has one inflection point. The identification of the flux function is of theoretical interest and practical importance for plant-scale simulators of continuous sedimentation. For a real suspension, the Kynch test and the Diehl test, which are based on an initially homogenous suspension either filling the whole settling column or being initially located above clear liquid, respectively, provide data points that represent curved (convex or concave, respectively) suspension-supernate interfaces from which it is possible to reconstruct portions of the flux function to either side of the inflection point. Several functional forms can be employed to generate a provably convex or concave, twice differentiable accurate approximation of these data points via the solution of a constrained least-squares minimization problem. The resulting spline-like estimated trajectory can be converted into an explicit formula for the flux function. It is proved that the inverse problem of flux identification solved this way has a unique solution. The problem of gluing together the portions of the flux function from the Kynch and Diehl tests is addressed. Examples involving synthetic data are presented.