Separation Of Small Particles Research Articles

Settling dynamics and thresholds for breakup and separation of bi-disperse particle clouds

Settling dynamics and thresholds for breakup and separation of bi-disperse particle clouds

Lab-based Martian analogue experiments investigating electric and magnetic fields of dust devils

Dust devils – rotating vortices of lofted particulates formed by convection from solar heating - are a prevalent aspect of Martian weather.Within a dust devil, particles become charged though triboelectrification, and observations of terrestrial dust devils have revealed electric and magnetic fields. Understanding the behaviour of these aeolian events is vital for mission planning and duration, for example, with the Insight lander as a prime example of a mission cut short due to obscuration of solar panels by lofted dust, which is highly likely to be charged. Charged dust devils on Mars strongly imply the existence of electric discharges due to the low breakdown field. The existence of discharges would in turn imply a global electric circuit on the planet – with implications for organic chemical formation and methane losses.This work presents a laboratory-based experimental set up for investigation into both electric and magnetic fields and the feasibility of using Martian analogue dust as alternative to in-situ measurements. In a dust devil, there are two main driving motions – a vertical separation of small and large particles, and the characteristic tight spiralling motion. The experimental set-up splits these components, allowing investigation into each. It is made up of a carefully designed cylindrical tank into which dusts or powders can be dropped to allow triboelectric charging as they fall under gravity. The base of the tank has a Faraday cup for charge measurement and there is also a field mill looking into the tank from the top. The rotational component is achieved using a paddle arrangement for samples placed in the base of the tank. Electric and magnetic fields have successfully been detected from charged dust with this system.

Apparent viscosity of high-density fluidized bed and synergistic effect of density and apparent viscosity on particle separation

ABSTRACT For gas-solid fluidization separation, mineral particles are separated under the joint action of bed density and apparent viscosity. In present study, the apparent viscosity of high-density binary mixture media was investigated by the falling ball method. Moreover, the significant effects of bed density and apparent viscosity on simulated mineral pellets and their interactions were investigated. The apparent viscosity model of high-density gas-solid fluidized beds was modified, and it was found that the Pearson correlation coefficient is 0.86. The results show that the apparent viscosity of high-density gas-solid fluidized bed decreases with increasing fluidization gas velocity. When the fluidization number is higher than 1.3, the apparent viscosity is basically stable in the range of 3.96–5.21 Pa·s. Under low apparent viscosity, when the pellet diameter is 20 mm and the density difference ∆ρ is greater than 0.27 g/cm3, gravity is the dominant factor affecting the settling behavior of the pellet. Under high apparent viscosity, the effect of viscous resistance on the settling behavior of pellets is dominant when the ∆ρ is less than 0.27 g/cm3. Based on the performed analyses, the low-viscosity medium can be selected for the separation of large mineral particles. Furthermore, for high-viscosity medium, the influence of bubbles on particle sedimentation can be effectively alleviated and it can be selected for the separation of small particles.

Non-Stop Switching Separation of Superfine Solid/Liquid Dispersed Phases in Oil and Water Systems Using Polymer-Assisted Framework Fiber Membranes.

Fabricating filtration membranes with wide applicability and high efficiency is always a challenge in the precise separation of small colloidal particles under mild conditions. For this purpose, a strategy mixing supramolecular framework fiber with polymer is adopted. The fibrous assembly in the gel state provides uniform nanopores for both channel and interception and controlled wettability for lyophilic/lyophobic switching. The used polymer fills the gaps between fiber assemblies and improves the mechanical property. The composite membrane shows both under-oil superhydrophobic and underwater superoleophobic nature, which allows the conversions via in situ modulation of joystick solvents. Based on surface wetting and size-sieving, ultrafine hard nanoparticles dispersing in both hydrophobic organic solvents and water are selectively sieved. In addition, on-demand separation of water-in-oil and oil-in-water microemulsions without and with surfactants as systems containing soft droplets are realized. The smallest cut-off size of ≈3nm is achieved for both hard and soft emulsions, while separation efficiency maintains during sustained in situ reversible switches.

INVESTIGATION OF THE INTENSIFICATION OF SEPARATION PROCESSES USING THE HEAT OF EXHAUST GASES

The useful use of heat for the above cases is primarily related to the use of heat from the exhaust gases. It should be stressed that in all cases it is necessary to return the maximum amount of waste heat to the process. Part of the heat is usually returned to the working chamber with heated air (up to 300 - 500 oC). In some cases, it is possible to use a certain amount of gas heat for drying and heating the raw material, the finished product and/or for heating the process water used in the processing; the use of heat from gases to produce steam and other parameters for the necessary heating of the blast furnace. All of this opens up the possibility of achieving very high end results for energy plants. However, as a rule, the exhaust gases are characterized by fairly high concentrations of fine solid particles (fine removals), which must be effectively removed in the separator because in most cases they prevent the efficient use of heat from the exhaust gases. Thus, efficient separation of fine removal is crucial for heat recovery of exhaust gases, especially for high-performance units. The ways to intensify the separation processes in industrial waste were investigated and made practical conclusions. Based on known literature data and results of own experiments, some questions of separation of fine removal are considered. The basics of the separation mechanism are formulated, which are reduced to elucidating the causes and patterns of movement of small particles to the separating surface across the main stream. The mechanisms of separation of small particles due to turbulent diffusion are analyzed in detail, the possibility of realization of the mechanism of separation on the basis of thermophoresis is estimated. The initial parameters and criteria that characterise the particle separation process have been established. A formula for assessing the particle separation rate is derived and the effect of the specified criteria on this value is analyzed. The analysis of the above dat a resulted in practical conclusions on ways to intensify the separation processes under industrial conditions.

Microplastics in Aquatic Environments: Recent Advances in Separation Techniques

Separation and removal of microplastic pollution from aquatic environments as a global environmental issue is classified as one of the major concerns in both water and wastewater treatment plants. Microplastics as polymeric particles less than 5 mm in at least one dimension are found with different shapes, chemical compositions, and sizes in soil, water, and sediments. Conventional treatment methods for organic separation have shown high removal efficiency for microplastics, while the separation of small microplastic particles, mainly less than 100 µm, in wastewater treatment plants is particularly challenging. This review aims to review the principle and application of different physical and chemical methods for the separation and removal of microplastic particles from aquatic environments, especially in water treatments process, with emphasis on some alternative and emerging separation methods. Advantages and disadvantages of conventional separation techniques such as clarification, sedimentation, floatation, activated sludge, sieving, filtration, and density separation are discussed. The advanced separation methods can be integrated with conventional techniques or utilize as a separate step for separating small microplastic particles. These advanced microplastic separation methods include membrane bioreactor, magnetic separation, micromachines, and degradation-based methods such as electrocatalysis, photocatalysis, biodegradation, and thermal degradation.

Development of an efficient rice De-stoner

One of the major staple foods consumed in Africa is rice. It has been discovered that it contained stones during the cause of processing which necessitate for rice destoner. This research was carried out to develop an efficient rice de-stoning machine. Therefore, among the work found in the literature, the two most efficient de-stoners were compared to others named Model A and B while the developed model was named KASO model. The components of the developed machine include feed hopper that houses the rice at the first stage of processing, two sieves of diameter 11.7 mm and 3 mm for wider separation, electric motor for torque transmission, and electric blower for separation of small particles. Stainless steel was selected for the interior due to its high corrosion resistance while mild steel was used for the exterior because of its high strength. The throughput and efficiency were measured and compared to the existing design. The results show that the KASO model yielded an efficiency and throughput of [91.4%, 46.57 kg⁄hr] compared to [98.3%, 11.46 kg⁄hr] and [82.47%, 47.39 kg⁄hr] for Model A and B, respectively.

Applicate Tangential Flow Filtration System to Improve Post CMP-Cleaning Performance

Chemical mechanical polishing (CMP) is one of the important process steps in semiconductor manufacturing. Several types of abrasives are used in the CMP process, among these, ceria slurry is commonly used through its excellent polishing performance in terms of oxide MRR. However, ceria particles remain on the wafer surface after polishing process as contaminants, and small ceria particles are difficult to remove from wafer surface [1].In this respect, we focused to treat small ceria particles that interfere with the cleaning process and we applicate the tangential flow filtration (TFF) system before the CMP process. TFF system is a system for separation of particles by Brownian motion, shear-induced diffusion and the mechanism shown in Fig. In this experiment, separation of small ceria particles successfully and it was evaluated by scanning mobility particle sizer (SMPS) analysis. Furthermore, TFF system did not affect the slurry properties of particle mean diameter, pH value, and zeta potential.In this study, concentration of ceria particles on the wafer surface after CMP process were evaluated by ICP-MS analysis. We calculated the cleaning efficiency with and without TFF separation system. As a result, cleaning efficiency was improved by using TFF system. In addition, the removal rate of SiO2 was almost maintained and the deviation decreased.

Modeling cross-flow ultrafiltration of permeable particle dispersions.

Cross-flow ultrafiltration is a pressure-driven separation and enrichment process of small colloidal particles where a colloidal feed dispersion is continuously pumped through a membrane pipe permeable to the solvent only. We present a semi-analytic modified boundary layer approximation (mBLA) method for calculating the inhomogeneous concentration-polarization (CP) layer of particles near the membrane and the dispersion flow in a cross-flow filtration setup with a hollow fiber membrane. Conditions are established for which unwarranted axial flow and permeate flow reversal are excluded, and non-monotonic CP profiles are observed. The permeate flux is linked to the particle concentration on the membrane wall using the Darcy-Starling expression invoking axially varying osmotic and trans-membrane pressures. Results are discussed for dispersions of hard spheres serving as a reference system and for solvent-permeable particles mimicking non-ionic microgels. Accurate analytic expressions are employed for the concentration and solvent permeability dependent dispersion viscosity and gradient diffusion coefficient entering into the effective Stokes flow and advection-diffusion equations. We show that the mBLA concentration and flow profiles are in quantitative agreement with results by a finite element method. The mBLA results are compared with predictions by an earlier CP layer similarity solution, showing the higher precision of the former method.

Confined Space Enables Spontaneous Liquid Separation by Molecular Size: Selective Absorption of Alkanes into a Polyolefin Cast Film

The depletion force has been used to explain phase separation phenomena in colloidal systems. Here, we showed that depletion force can explain not only phase separation of large and small colloidal particles but also preferential absorption of larger molecules from a mixture of large and small molecules in a liquid state. When a polyolefin cast film was immersed in a mixture of long and short normal alkanes, the longer molecules were selectively absorbed into the film. This experimental result was explained from the viewpoint of depletion force. The main finding was the use of confined space to emphasize the separation tendency caused by the force. In general, the increase in entropy may serve as a driving force to mix molecules. However, if sufficiently narrow pores are present, large and small molecules are separated naturally by size as the entropy increases. This finding will lead to size exclusion chromatography of low-mass molecules, similar to gel permeation chromatography of macromolecules. In order to demonstrate the effect of depletion force, we selected and experimented with a system based on a polyolefin isotactic poly(4-methyl-1-pentene) (P4MP1) film and a normal alkane mixture and realized high molecular selectivity. The P4MP1 film we used can be prepared simply by evaporating the solvent from the solution and casting the film. On the basis of the Asakura-Oosawa theory, we concluded that spontaneous and high molecular selectivity is attributed to the depletion force provided by the small sub-nanopores with uniform size in the film.

Liquid Crystals-Enabled AC Electrokinetics.

Phenomena of electrically driven fluid flows, known as electro-osmosis, and particle transport in a liquid electrolyte, known as electrophoresis, collectively form a subject of electrokinetics. Electrokinetics shows a great potential in microscopic manipulation of matter for various scientific and technological applications. Electrokinetics is usually studied for isotropic electrolytes. Recently it has been demonstrated that replacement of an isotropic electrolyte with an anisotropic, or liquid crystal (LC), electrolyte, brings about entirely new mechanisms of spatial charge formation and electrokinetic effects. This review presents the main features of liquid crystal-enabled electrokinetics (LCEK) rooted in the field-assisted separation of electric charges at deformations of the director that describes local molecular orientation of the LC. Since the electric field separates the charges and then drives the charges, the resulting electro-osmotic and electrophoretic velocities grow as the square of the applied electric field. We describe a number of related phenomena, such as alternating current (AC) LC-enabled electrophoresis of colloidal solid particles and fluid droplets in uniform and spatially-patterned LCs, swarming of colloids guided by photoactivated surface patterns, control of LCEK polarity through the material properties of the LC electrolyte, LCEK-assisted mixing at microscale, separation and sorting of small particles. LC-enabled electrokinetics brings a new dimension to our ability to manipulate dynamics of matter at small scales and holds a major promise for future technologies of microfluidics, pumping, mixing, sensing, and diagnostics.

Measurement of Subcellular Metabolite Concentrations in Relation to Phloem Loading.

The key step of carbon export from green leaves is the loading of sugars into the phloem. To fully understand and quantify this process, it is essential to know the concentration of sugars in the different compartments of the cells along the phloem loading pathway. However, determining subcellular metabolite concentrations has been technically challenging. This paper describes a technique to measure metabolite levels in the chloroplast, the cytosol, and the vacuole of mesophyll cells with high accuracy. The nonaqueous fractionation (NAF) technique is arguably the method of choice to analyze the subcellular metabolite distributions as it minimizes the risk of metabolite interconversions or redistribution during the process. The principle of NAF is the separation of small subcellular particles, which are obtained by homogenization, lyophilization, and sonication, in a nonaqueous density gradient. Due to the varying composition-dependent density of the fragments, their segregation reflects compartmental distributions throughout the gradient. By determining marker enzymes for chloroplast stroma, cytosol, and vacuole in gradient fractions the proportions of each subcellular compartment in each gradient fraction can be analyzed. The measured distribution of marker enzymes and of metabolites in each fraction of the gradient can be used to calculate the subcellular distribution of the metabolites.

Simulation of jet cleaning: Diffusion model for swellable soils

A physical-numerical simulation model for the cleaning of swellable soils by diffusive dissolution or cohesive separation of small soil particles, which was developed targeting a low computational effort, is presented and validated. The flow calculation, based on the Reynolds averaged Navier Stokes equations (RANS), and the calculation of the soil transport, modelled following the unsteady RANS concept, are performed successively. The behaviour of the soil is modelled as a transient Dirichlet boundary condition, its parameters being determined in laboratory experiments using plane channel flow. A validation is performed for a coherent water jet impinging vertically on a substrate, which is covered by a starch-based model soil, at a distance of 100mm to the nozzle. Using a nozzle diameter of 1.69mm and pressures in the nozzle ranging from 1.5 to 5bar, corresponding to Reynolds numbers between 17700 and 55600, the wall shear stress in this configuration exceeds the values given in the laboratory tests by two orders of magnitude. Despite this difference, the simplicity of the model and the complexity of the test case, the simulated cleaning times correspond very well to the measured values. Thus, the targeted scalability and transferability of the model to other flow configurations are ensured.

Separation of Small Particles by Diffusio‐ and Thermophoresis in a Gas‐Liquid Cross‐Flow Array

AbstractA wet scrubber technique was studied for the separation of particles < 2.5 μm from exhaust gas by a gas‐liquid cross‐flow array. The cleaning water of the separator flows vertically down along many regularly configured wires and the generated water film acts as an independent sink for particle collection. Due to the surface‐orientated horizontal particle movement caused by diffusio‐ (DP) and thermophoresis (TP), the particles can be captured by the water films. Since wastewater from the same production process can be used, the necessary cleaning water recycling costs can be saved due to the already available water treatment device. Experiments on a laboratory‐scale test rig show the particle grade removal efficiency (PGRE) for different inlet gas‐water temperature gradients and for a constant vapor injection.

Challenges in Modelling and Control of Offshore De-oiling Hydrocyclone Systems

Offshore de-oiling installations are facing an increasing challenge with regards to removing oil residuals from produced water prior to discharge into the ocean. The de-oiling of produced water is initially achieved in the primary separation processes using gravity-based multi-phase separators, which can effectively handle large amounts of oil-well fluids but may struggle with the efficient separation of small dispersed oil particles. Thereby hydrocyclone systems are commonly employed in the downstream Produced Water Treatment (PWT) process for further reducing the oil concentration in the produced water before it can be discharged into the ocean. The popularity of hydrocyclone technology in the offshore oil and gas industry is mainly due to its rugged design and low maintenance requirements. However, to operate and control this type of system in an efficient way is far less simple, and alternatively this task imposes a number of key control challenges. Specifically, there is much research to be performed in the direction of dynamic modelling and control of de-oiling hydrocyclone systems. The current solutions rely heavily on empirical trial-and-error approaches. This paper gives a brief review of current hydrocyclone control solutions and the remaining challenges and includes some of our recent work in this topic and ends with a motivation for future work.

Sieve-based lateral displacement technology for suspension separation

Sparse lateral displacement arrays are easier to scale up than full deterministic lateral displacement arrays or deterministic ratchets, because they require lower pressure drop and simplify the construction of the device. However, the asymmetry of sparse arrays leads to a non-homogeneous pressure distribution with as a consequence an uneven flow field and limited separation performance. Furthermore, the construction of high throughput displacement sparse ratchet devices that allow separation of small particles is challenging. Therefore, in this study we investigated the use of sieves to replace obstacles in sparse systems. Moreover, we investigated a strategy to optimize the separation performance by adjusting the internal pressure distribution. Our experiments showed in first instance that the introduction of sieves negatively affects separation performance, which was explained by the lower porosity of the sieves. However, via fluid flow calculations and high-speed camera analyses we found that pressure distribution can be optimized by adapting the flow rates of the different outlets preventing high pressure drop across the obstacles arrays near the bottom of the device. Experimental separation data for adjusted outlet flow conditions indeed showed better particle displacement, especially in the bottom region, and as a result improved separation behavior. These findings demonstrate the potential of the scalable sieve-based lateral displacement device to effectively separate particles.

CFD Simulations of Pressure Drop and Velocity Field in a Cyclone Separator with Central Vortex Stabilization Rod

A problem of cyclone separators is the low grade efficiency of small particles. Therefore, a high efficiency cyclone separator has been developed and successfully tested in former work. In this cyclone separator, a vortex stabilizer is used to suppress the vortex core precession. In this article, the pressure and flow field in this cyclone separator are calculated by means of computational fluid dynamics using the commercial software Ansys Fluent 13. The position of the vortex core is tracked in these simulations by searching the position of minimal dynamic pressure and the centre of moment of the horizontal velocity components as function of the axial coordinate. The results are compared with experimental data. It is demonstrated that when using a stabilizer, the vortex is kept in position. Furthermore the maximum of the tangential velocity is found to be larger, which is known to have a positive effect on the separation of small particles in the inner solid body rotation vortex.

Separation of small solid particles based on ultrasonic rotary driving

In this work, we proposed and developed an ultrasonic actuator which can be used to separate mixed small solid particles in air. The device consists of an ultrasonic sandwich-type transducer and an aluminum plate which is extended from an end plate of the transducer. The aluminum plate is asymmetrically excited by the transducer, to vibrate flexurally. The transducer operates in the thickness mode and has a resonance frequency of 91.7kHz. Particle mixtures used in the experiments are obtained by the combination of any two particles among shrimp eggs, glass balls and salt particles. The experiments showed that the glass balls could be separated from a mixture of glass balls and shrimp eggs, and salt particles separated from a mixture of salt particles and shrimp eggs. The device used in the method has no mechanical rotary part and the separation can be quickly completed.

Hydrodynamic separation of particles using pinched‐flow fractionation

Rigid particles transported through a pinched‐flow fractionation (PFF) device are simulated using boundary‐integral methods (BIM). The PFF device separates particles by size using a bifurcated microfluidic channel. The critical flow ratio of the two input channels required to achieve complete separation of large and small particles decreases with increasing diameter of the larger particles relative to the pinch height, and is nearly independent of the smaller particle size. A narrow pinch with a square exit was shown to have the lowest critical flow ratio and was selected as the model device to be fabricated. Experiments conducted using this device confirm that the larger particles exit further from the top wall than do the smaller particles, due to steric exclusion, and the final exit positions are within a few percent of the simulation results. It is shown that BIM is a valuable tool in the design of microfluidic devices. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3444–3457, 2013

Numerical modeling of a nonmonotonic separation hydrocyclone curve

In the context of the mechanics of interpenetrating continua, numerical modeling of separation of a polydis- perse suspension in a hydrocyclone is carried out. The so-called "mixture model" valid for a low volume frac- tion of particles and low Stokes numbers is used for description of the suspension and particle motion. It is shown that account taken of the interaction between large and small particles can explain the nonmonotonic behavior of the separation curve. Introduction. To characterize the efficiency of separation of small and large suspension particles in hydrocy- clones one uses the separation curve T(d) which shows the share of particles of each fraction of the suspension intro- duced into the apparatuses that are removed through the lower nozzle of a classification apparatus (Fig. 1). It follows from classical representations of the dependence of the rate of sedimentation of a particle on its size d p (1-3) that the separation curve T(d) is monotonically increasing from a certain value T(0) < 1 at d p → 0 to T = 1 at d p → ∞. This representation is based on the fact that as the size of particles increases, their sedimentation rate rises; therefore, the larger the particles, the more they can be drawn to the wall of the apparatus and taken out through the lower outlet. Indeed, it has been repeatedly noted, e.g., in (3-12), that the separation curve has a minimum in the range of particle size from 10 μm and lower. This behavior of the curve is called the "fish-hook" effect. It has not been given an unambiguous explanation to date. There are several versions of interpretation of this phenomenon in the literature: insufficiently accurate granulometric analysis; dependence of the materials' density on the particle size; flocculation and agglomeration of the dispersed material; hydrodynamic interaction of particles of various size. The analysis of the causes of the "fish-hook" effect in (13) leads to the conclusion that it is only hydrody- namic interaction of particles that can serve as a source of nonmonotony of the separation function. Hydrodynamic mechanisms of the manifestation of a "fish-hook" effect are discussed in the literature (6, 8-12) but basically at the qualitative level, which only results, as a rule, in the formulation of some empirical formulas. This helps characterize the classification process but it does not explain the phenomenon. Investigations (14) have been carried out in recent times which formulate the concepts that suggest that the abnormal motion of small particles in the apparatus is caused by the stochastic motion of particles under con- ditions of turbulence. Accordingly, stochastic models of the phenomena are constructed, whose implementation re- quires the involvement of numerical methods. At the same time, the interaction of particles of various fractions between each other is either not taken account of (14) or hypotheses are adopted that are not corroborated in ex- periments. The importance of a correct account of the said interaction is obvious if only because the parameters of the "fish-hook" effect depend on both the concentration of the solid phase in a suspension and on the granulomet- ric composition of a material. Using the below kinematic model of acceleration of sedimentation of small particles at the expense of large ones (15, 16), not only is explanation given to the anomalous behavior of the separation curve at small values of the particle size (this explanation has already been given in simplified form (11-13)) but a calculation is also provided of the separation curve for a hydrocyclone. At the same time, the manifestation of a "fish-hook" effect is illustrated at