Particles Of Different Densities Research Articles

Effect of nano-SiC on microstructure evolution and enhanced high wear resistance mechanism of laser surface alloyed M42 high-speed steel

M42 high-speed steel is one of the main materials for preparing bimetallic band saw parts. In this paper, nano-SiC particles of different densities (0–1.00 mg/mm2) were precoated on the surface of M42 high-speed steel samples, then, the samples were prepared by laser alloying. The matching relationship between the quantity, size, and type of martensite and MxCy carbides in laser alloyed samples play a decisive role in improving wear resistance. It is found that under the optimized particle density of 0.75 mg/mm2, compared with M42 high-speed steel, the hardness was increased by 50%, the wear rate decreased by 84.7%. The matching relationship between Martensite and MxCy carbides formed by laser alloying of nano-SiC particles on the improvement of wear resistance was elucidated.

Segregation of binary particles in pulsed gas-solid fluidized bed

Pulsating airflow-driven gas-solid fluidization is an effective method to segregate particles of different densities. The current article presents an elaborate computational study on the development of simulation methodology, and parametric trend identification of pulsating airflow-driven granular segregation for the first time using computational fluid dynamics (CFD), discrete element modeling (DEM) coupled analysis. The rigorous validation of the computational prediction has been produced against the experimental result reported by Li et al. (2021) and an excellent agreement has been observed. Segregation behavior for different density ratios of particles, different patterns of pulsation, and different particle shapes is presented in the current article. The segregation index improves with the density ratio of the binary mixture of particles, but the rate of increment of the segregation index is highly dependent on the airflow rate. Near the optimal value of airflow rate, the rate of increment of the segregation index reduces with the density ratio. Keeping the bed height and material property constant, different patterns of pulsation namely—sinusoidal, triangular, and exponential have been adopted. The segregation index is higher for sinusoidal patterns, whereas it reduces when the pattern is changed to triangular and exponential. Particles of constant volume with different shapes are also considered to understand the effect of particle shape on segregation. The segregation index deteriorates with the increasing surface area of the particle at constant volume.

Effects of Apex Size on Dissolution Profiles in the USP II Paddle Apparatus

The use of apex vessels may solve coning problems associated with dissolution testing. However, excessive dissolution acceleration can reduce the discriminatory power. This study aimed to clarify how different apex vessel sizes affect the dissolution behavior of cone-forming formulations. Five apex vessels with different heights, centralities, and compendial vessels were used. The paddle rotation speed at which the coning phenomenon resolved was measured using standard particles of different densities. Three model formulations—USP prednisone tablets, atorvastatin calcium hydrate tablets, and levofloxacin fine granules—were selected, and dissolution tests were conducted at 30–100 revolutions per minute (rpm). Compared to the compendial vessels, the disappearance of standard particles at the apex base at lower paddle speeds in apex vessels was observed. Standard particles tended to remain in the center of the apex vessels and disappear at rotational speeds comparable to those of the compendial vessels. Dissolution increased in an apex height-dependent manner in the model formulations, except for the atorvastatin calcium hydrate tablets at 50 rpm. For levofloxacin fine granules, dissolution was also improved by reducing the paddle agitation speed to 30 rpm in the compendial vessels. Differences in apex centrality by 3 mm did not affect the dissolution rate. Our results indicate that apex vessels with low apex heights have a mount-resolving effect, but the degree of dissolution improvement by avoiding the coning phenomenon depends on the formulation characteristics used in the dissolution tests.Graphical abstract

Mechanistic Observation of Interactions between Macrophages and Inorganic Particles with Different Densities.

Many different types of inorganic materials are processed into nano/microparticles for medical utilization. The impact of selected key characteristics of these particles, including size, shape, and surface chemistries, on biological systems, is frequently studied in clinical contexts. However, one of the most important basic characteristics of these particles, their density, is yet to be investigated. When the particles are designed for drug delivery, highly mobile macrophages are the major participants in cellular levels that process them in vivo. As such, it is essential to understand the impact of particles' densities on the mobility of macrophages. Here, inorganic particles with different densities are applied, and their interactions with macrophages studied. A set of these particles are incubated with the macrophages and the outcomes are explored by optical microscopy. This microscopic view provides the understanding of the mechanistic interactions between particles of different densities and macrophages to conclude that the particles' density can affect the migratory behaviors of macrophages: the higher the density of particles engulfed inside the macrophages, the less mobile the macrophages become. This work is a strong reminder that the density of particles cannot be neglected when they are designed to be utilized in biological applications.

Eulerian simulations of bubbling and jetting regimes in a fluidized bed

The mode of gas-injection is known to influence the local bubbling and jetting behavior in gas–solid fluidized beds. The resultant bubbling behavior influences the mixing and distribution of the gas and solid phases, which in turn can influence heat and mass transfer, and reaction performance in large-scale gas–solid fluidized beds. In the present work, we simulated unary gas–solid flow of particles differing in density, fluidized using uniform and two-jet distributors at different UG. The predictions are validated using the measured local gas-phase area fraction fluctuations, bubble size distribution, and bubble rise velocity. The effect of the models used for calculation of gas–solid drag (βgs), solids frictional pressure (Ps,f), and specularity coefficient (φ) on the bubbling characteristics under dense and dilute flow conditions are analysed. Under dense bed condition (UG = 1.1 Umf), an increase in the Ps,f and φ led to an increase in solids viscosity, which in turn led to a decrease in the bubble rise velocity and size. In the case of the two-jet distributor, an increase in βgs predicted merging of the larger jets and formation of larger bubbles. Further, to predict the different jetting regimes (isolated jets, breakage/merging of jets, and generation of larger bubbles) at different UG correctly, we show that different βgs models are required. Whereas, in the case of gas–solid flows comprised of particles of different density fluidized with the uniform distributor, a single βgs model predicted the bubbling characteristics reasonably well with measurements.

Study of classification processes of various bulk geomaterials in a hydrodynamic environment using laboratory models of counter-current drum separators

The paper presents the results of studying separation processes of various mineral particles of different density in a hydrodynamic (water) environment in three laboratory models of counter-current drum separators with cylindrical, conical and multifaceted drums. Research results have shown that compared to cylindrical and conical drum separators, the multifaceted separator is most effective in separating and refining in a hydrodynamic environment. The high recovery of heavy minerals in the concentrate proves this fact.

Dermal integration of hyaluronic acid fllers: observation in real clinical practice

A clinical observation of the dermal integration of low-concentration products based on hyaluronic acid produced by KPM and IPN-Like technologies is presented. KPM technology is a method of obtaining a cohesive poly-compacted gel matrix of hyaluronic acid, which determines the peculiarity of distribution in the skin due to particles of different densities in one product. On the one hand, the drug remains at the injection site after injection due to dense particles, on the other hand, translocation of loose particles into a more modifed part of the dermis. The clinical effect is manifested in the form of full integration of the drug into the dermis, imitating natural volumes. IPN-Like technology involves the preparation of a hyaluronic acid preparation from two monophase chains with low and high elasticity. Interpenetrating stabilized chains are obtained under pressure. Partial independence of IPN structures is necessary for the predicted integration and distribution of the drug in tissues, whereas the increased density of cross-linking nodes strengthens the intensity of the chemical bond, strengthens the fxation of the drug at the injection site. The study was conducted on seven patients using ultrasound scanning before the procedure, during the procedure to control the introduction into the required layer, 15 minutes after the procedure and 2 months later. To objectify the data, skin proflometry was used and photodocumentation in the designated time frame. In the presented clinical case, when comparing the distribution of fllers based on hyaluronic acid, it was revealed that all drugs are well distributed in the surface layers of the dermis, which makes it possible to safely inject drugs created using IPN-Like technology in the same techniques and to the same depth as the drug with CPM technology. According to ultrasound of the skin, drugs produced by IPN-Like technology showed greater effectiveness in terms of dermis thickness after 2 months.

Influence of the properties of solid particles added to a structured suspension on its dynamic sedimentation stability

The research paper analyzes previous studies of the influence of two natural relatively pure aluminum oxides on rheological properties of structured suspensions. The results of the research show that the content of these materials in the mineral part of coal contributes to a decrease in viscosity inversely proportional to the ash content of coal to a certain fractional degree. The analysis showed that the effect of additions of mineral particles, their size and concentration on the dynamic or static sedimentation stability of structured suspensions has never been studied. The aim of the research paper is to study the effect of additions of mineral particles of polydisperse granulometric composition of different nature on the dynamic sedimentation stability of a structured suspension of high-ash coals. The solution of the problem is carried out by comparison of the forces of attraction and repulsion, which are characterized by an ion-electrostatic and van der Waals nature, with the forces , which arise when a fluid flows around two particles of different density and size, with taking into account the turbulent component and speed deficits proportional to the hydraulic sizes of interacting particles. As a result of the research, the authors developed and specified the hypothesis of the mechanism of aggregative stability of a structured suspension in dynamics. It takes into account the heterogeneity of the properties of particles of the solid phase, which made it possible to establish the value of the average flow velocity in a circular tube, at which the aggregative stability of a structured suspension is disturbed. It is found that the particle size, the nature of the solid material and its mineral inclusions, their surface potential, and rheological characteristics are the main factors, which determine the aggregative stability of structured suspensions. The influence of rheological characteristics of the structured suspension and the radius of the pipeline on the flow velocity, at which its aggregative stability was disturbed, was studied for the case when the solid phase was represented by particles with different density and fineness. In addition, the minimum possible ratio of the Archimedes parameters of the interacting particles, at which the effect of pseudo-homogeneity occurred, was evaluated.

Editorial for Special Issue “Gravity Concentration”

Gravity concentration is the process by which particles of different densities, sizes, and shapes separate from each other when under the action of gravity or centrifugal forces [...]

Sedimentation of Two Side-by-Side Heavy Particles of Different Density in a Shear-Thinning Fluid with Viscoelastic Properties

Particle sedimentation has widely existed in nature and engineering fields, and most carrier fluids are non-Newtonian. Recently, the manipulation of a settling particle in liquid has been a topic of high interest to those involved in engineered processes such as composite materials, pharmaceutical manufacture, chemistry and the petroleum industry. Compared with Newtonian fluid, the viscosity of non-Newtonian fluid is closely related to the shear rate, leading to a single settling particle having different dynamic behaviors. In this article, the trajectories and velocities of two side-by-side particles of different densities (heavy and light) settling in a shear-thinning fluid with viscoelastic property were studied, as well as that for the corresponding single settling particle. Regardless of the difference in the particle density, the results show the two-way coupling interaction between the two side-by-side settling particles. As opposed to a single settling particle, the wake of the heavier particle can clearly attract or rebound the light particle due to the shear-thinning or viscoelastic property of the fluid. Regarding the trajectories of the light particle, three basic path types were found: (i) the light particle is first attracted and then repelled by the wake of the heavy one; (ii) the light particle approaches and then largely traces within the path of the heavy one in the limited field of view; (iii) the light particle is first slightly shifted away from its original position and then returns to this initial position. In addition to this, due to the existence of a corridor of reduced viscosity and negative wake generated by the viscoelastic property, the settling velocity of a light particle can exceed the terminal velocity of a single particle of the same density. On the other hand, the sedimentation of the light particle can induce the distinguishable transverse migration of the heavy one.

Segregation and mixing behavior of geldart D binary particles in pulsed gas-solid fluidized bed

Gas-solid fluidized bed is an effective dry method for beneficiation of −6mm fine coal, belonging to Geldart D particle. Due to the density difference of concentrates and gangue in the raw coal, the bed can remove gangue through segregation of binary particles. The core problem is how to reduce the bubble coalescence and improve segregation degree in the bed. In this study, glass beads and plastic beads were selected to simulate high-density and low-density particles in pulsed gas-solid bed (PGFB). And different pulsation frequencies (f = 0–7 Hz) and gas velocities (N = 1.1–1.7) were selected in this work. The results showed that gas velocity and pulsation frequency played important role on particle segregation and mixing behavior. The segregation index reached the maximum value at pulsation frequency f = 3.49 Hz and gas velocity N = 1.3 when h = 80 mm, indicating pulsed gas-solid fluidized bed can effectively separate particles of different densities. With the increase of bed height, the standard deviation of separation index decreases, and the optimal frequency moves to the low frequency region. This work provides guidance for the study of segregation and mixing behavior of Geldart D binary particles in pulsed fluidized bed.

Taking a mass-balance approach to assess marine plastics in the South China Sea

The South China Sea (SCS) is recognised as a global hotspot for plastic pollution. We review available field studies and identify a significant lack of data needed to construct a simple mass balance box model for plastic pollution in the SCS. Fundamental information on plastic mass input, transfer and sink terms are simply not available. Also unknown are the rates of accumulation in different environments, the dispersal pathways of plastic particles of different density, the residence times of plastic in the water column and the rate at which macroplastics are transformed into microplastics in different environments. Filling these information gaps is critical for states to determine adequate response measures, including developing and tracking impact of policies to deal with the problem of plastic pollution in the SCS.

The performance of an acoustic levitator

An acoustic levitator uses an array of ultrasonic transducers to generate a standing acoustic pressure field which exerts a radiation force on small particles, allowing the particles to be trapped, relocated, separated or combined. Experiments on levitating particles of different densities and calculations of the acoustic radiation force and moment have been reported in the literature. However, direct inspection on the acoustic pressure field pattern is seldom carried out. This paper reports an investigation on the performance of an existing acoustic levitator design, which uses off-the-shelf components, by comparing the visualized pressure field from Schlieren imaging to analytical simulations. The ability to compare Schlieren imaging results to analytical simulations readily can prove to be a vital tool. Since the simulations provide an ideal pressure field, the imaging of the levitator pressure field can highlight discrepancies between the real and ideal cases. This can be especially useful as a diagnostic tool to identify the cause of a drop in performance of the acoustic levitator in a real world scenario.

Effect of materials on hydrodynamics of cone-shaped inverse fluidized bed by experimental and CFD simulations

Abstract In the Present work, we have investigated the hydrodynamic behavior of cone-shaped tapered inverse fluidized bed using different spherical particles of different densities by changing the liquid velocity of continuous flow from the top of the bed. The experimental results were also compared with the results of Ansys fluent 17.2 software of Computational fluid dynamics (CFD) simulations in 2-dimensional geometry. The effects of bed expansion ratio and bed pressure drop on the performance of bed were also investigated both experimentally, and numerically. The Gidaspow drag function was used for numerical investigations in CFD simulations.

Helicoidal particles in turbulent flows with multi-scale helical injection

We present numerical and theoretical results concerning the properties of turbulent flows with strong multi-scale helical injection. We perform direct numerical simulations of the Navier–Stokes equations under a random helical stirring with power-law spectrum and with different intensities of energy and helicity injections. We show that there exists three different regimes where the forward energy and helicity inertial transfers are: (i) both leading with respect to the external injections, (ii) energy transfer is leading and helicity transfer is sub-leading and (iii) both are sub-leading and helicity is maximal at all scales. As a result, the cases (ii)–(iii) give flows with Kolmogorov-like inertial energy cascade and tuneable helicity transfers/contents. We further explore regime (iii) by studying its effect on the kinetics of point-like isotropic helicoids, particles whose dynamics is isotropic but breaks parity invariance. We investigate small-scale fractal clustering and preferential sampling of intense helical flow structures. Depending on their structural parameters, the isotropic helicoids either preferentially sample co-chiral or anti-chiral flow structures. We explain these findings in limiting cases in terms of what is known for spherical particles of different densities and degrees of inertia. Furthermore, we present theoretical and numerical results for a stochastic model where dynamical properties can be calculated using analytical perturbation theory. Our study shows that a suitable tuning of the stirring mechanism can strongly modify the small-scale turbulent helical properties and demonstrates that isotropic helicoids are the simplest particles able to preferentially sense helical properties in turbulence.

Magnetic projection: A novel separation method and its first application on separating mixed plastics

A novel magnetic separation method, denoted as “magnetic projection”, was proposed. The method is based on a simple configuration: a container full of paramagnetic medium is placed beside a permanent magnet. Particles of different densities that submerge in the medium are driven by the magnetic force, moving in accordance with different trajectories, and are finally landed in different collection regions. We applied this method to separate mixed plastics, because most of the extant plastic separation processes can only deal with binary mixture. In the experiment, four common plastics such as polyvinyl chloride (PVC), polyethylene terephthalate (PET), polycarbonate (PC), and polymethyl methacrylate (PMMA) were used to simulate the plastic mixture. The experimental results showed that the proposed method can effectively separate the plastic mixture, as the purity of each type of recovered plastics was over 95 wt%. This approach demonstrates its tremendous potential in solid waste management and worth further investigation.

Spouting behavior of binary particle mixtures of different densities: Fluid dynamics and particle segregation

Numerous industrial applications of spouted beds involve a mixture of granular particles, where differences in particle size, density, and shape can cause particle segregation, affecting the quality of flow and decreasing product homogeneity. The aim of this study was to investigate the particle segregation and fluid dynamics of a conical spouted bed operating with a binary mixture of particles of different densities. Using glass beads and polyethylene particles with a diameter of 4mm, we determined the effects of the mass fraction of denser particles and static bed height on the minimum spouting condition and mixture index. The pressure drop and airflow in the minimum spouting condition increased with an increase in bed height or jetsam concentration. Regarding particle segregation, the jetsam particles tended to concentrate near the bottom, at the spout–annulus interface because they have a shorter trajectory than the lighter particles in the fountain region. Jetsam-rich mixtures with high initial static bed heights exhibited more efficient particle mixing, excluding those at the bottom of the bed.

Study of Conditions of Binary Particle Mixture Motion Applied to Chemical Looping Combustion of Fuel with Carbon Dioxide Capture

Chemical looping combustion and gasification of fuels with using metal oxides as oxygen carriers is a rapidly developing technology for capturing carbon dioxide. This technology is based on the use of interconnected reactors with a fluidized bed and circulating fluidized bed. Crucial in the technology is the reliable security of a high solid circulation rate between the reactors to maintain the desired temperature. When burning solid fuels, ash particles inevitably enter the metal oxide stream. This can lead to a change in the hydrodynamic parameters of an interconnected reactor system. In this paper, we present the results of an experimental study of fluidization conditions and hydrodynamics of a reactor with a circulating fluidized bed under motion conditions of binary mixtures of particles with different density. We also justified the conditions for simulating the particle sizes of heavy and light fractions as well as their mass in the reactor and a portion of a light fraction. We showed that, at a small addition of a light fraction, the minimum fluidization rate decreases markedly. Particle segregation was observed for large metal oxide particles, while light particles were found to be near the layer surface. The addition of a light fraction with a mass fraction of 3–12% does not significantly affect the mass flow profile of particles in a circulating fluidized bed reactor. The fractional composition of the particles in both the upward flow in the center and the downward stream near the walls of reactor is approximately the same. In the central part of the riser, the concentration of the light fraction was found to be slightly higher than its average value. The obtained results support the possibility of using the previously developed dependences for the calculation of hydrodynamics under motion conditions of binary mixtures of particles of different densities in the presence of a light fraction of 3–12%.

A soft-sensor approach to mixing rate determination in powder mixers

Mixing of powders is of great importance in food, chemical and pharmaceutical industries. However, direct online measurement of mixing is impractical due to difficulties in real-time particle sampling. In such systems, soft-sensors placed external to the equipment may be used to indirectly determine the behaviour of the system using relationships between internal and external phenomena. In this paper, a soft-sensor approach is studied for a ribbon powder mixer with 0, 2, 4 and 6 impeller spokes, and 20, 30, 40 and 50% volumetric particle filling, using two types of particles of different densities and a fixed impeller speed of 100 RPM. The particle data are based on DEM simulation results in a previous study. Force sensors along the underside of the mixer identify the number of particle-wall contacts and the force experienced by the sensors during the DEM simulations. This information is used along with mixing data to determine a relationship between external force data and internal mixing behaviour. The dividing rectangles global optimisation technique is used to approximate the mixing rate coefficient from particle data, and principal component analysis is used to develop a fast and practical means to estimate the mixing rate coefficient using only readings from external force sensors. This approach is then extended to allow for real time estimation of the required mixing time.

Segregation of a binary granular mixture in a vibrating sawtooth base container.

A granular mixture of identical particles of different densities can be segregated when the system is shaken. We present an efficient method of continuously segregating a flow of randomly mixed identical spherical particles of different densities by shaking them in a quasi-two-dimensional container with a sawtooth-shaped base. Using numerical simulation we study the effect of direction of shaking (horizontal/vertical), geometry of the sawtooth, and the friction coefficient between the grains and the container walls on the segregation quality. Finally by performing experiments on the same system we compare our simulation results with the experimental results. The good agreement between our simulation and experiment indicates the validity of our simulation approach and will provide a practical way for granular segregation in industrial applications.