Inert Particles Research Articles

The engulfment of a precipitated particle in a saturated melt during solidification

A rigorous, finite-element model is employed to study the engulfment of a precipitated solid particle during solidification in a saturated melt, in which solute segregation, compositional effects on melting temperature, and reaction of the solute with the particle occur. The case of a silicon carbide (SiC) particle approaching a solid–liquid interface in a silicon melt supersaturated with carbon is specifically considered. Critical engulfment velocities are computed for particles with different surface reaction rates, as characterized by the Damköhler number, a dimensionless ratio of reaction to diffusion. Consistent with prior studies, an inert particle is predicted to be less likely to be engulfed when solute effects are present. However, a particle with fast surface reaction is more likely to be engulfed than in a system without solute effects, which is likely relevant for SiC particles during silicon crystal growth. Most interestingly, a particle for which the surface reaction is characterized by a Damköhler number of order unity is predicted to never be engulfed.

Глубина прогрева потока газовзвеси встречным излучением

Выполнена аналитическая оценка отношения глубины прогрева газовзвеси излучением продуктов горения S к длине свободного пробега излучения в газовзвеси L. Использована одномерная модель стационарного распределения температуры в потоке взвешенных в воздухе монодисперсных инертных частиц, движущихся на равномерно нагретую абсолютно черную поверхность, имитирующую фронт пламени. Учитывается отражение и переизлучение тепловой энергии частицами. S / L >> 1 при низкой степени черноты и/или высокой конечной температуре частиц. It is accepted that the depth of heating of the gas suspension by the radiation of combustion products SR is equal to the length LR of the free path of radiation in the gas suspension: SR ≈ LR. Numerical simulation of gas-air mixture combustion with the addition of inert particles, taking into account the re-emission of heat by heated particles of fresh suspension, shows the possibility of realizing the ratio SR >> LR (Ivanov M.F. et al, 2015). In this work, an analytical estimate of the SR/LR ratio is carried out within the framework of one-dimensional modeling of the temperature distribution in the flow of initially cold monodisperse inert particles suspended in air, moving to a uniformly heated absolutely black surface, permeable to air suspension and simulating a flame front. The following assumptions are used. The solution is stationary in the coordinate system associated with the emitting surface; radiation consists of two oppositely directed streams of electromagnetic energy; the interaction of particles and radiation is described in the approximation of geometric optics and takes into account both the processes of absorption and emission of thermal energy, and the process of reflection of radiation; the temperature inside the particle is the same. In contrast to the previously considered (Poletaev N.L., 2021) the simplified problem of the motion of particles in a vacuum or in the presence of a gas phase heated by particles but not experiencing thermal expansion, this work took into account both the presence of a gas phase heated by particles and expansion of the gas phase. The latter causes the acceleration and expansion of the air suspension as it approaches the radiating surface. The difference in the local values of temperatures and phase motion velocities of the air suspension was neglected. It is shown that the quasi-linear (in the above-mentioned coordinate system) temperature distribution function in the air suspension obtained in this work is qualitatively different from the quasi-exponential temperature distribution function obtained earlier by solving a simplified problem. At the same time, the ratio of the heating depth of the air suspension by thermal radiation and the free path of radiation in the layer of air suspension adjacent to the radiating plane turned out to be similar to that obtained for the simplified solution. Namely, SR/LR >> 1 at a low integral degree of emissivity of the particle material and / or at a high final temperature of the particles, comparable to the temperature of the emitting surface.

Solar-driven gasification in an indirectly-irradiated thermochemical reactor with a clapboard-type internally-circulating fluidized bed

A 7-kWth indirectly irradiated solar gasifier with a clapboard-type internally circulating fluidized bed was developed and conducted experimentations under concentrated solar radiation. The solar CO2 gasification of charcoal produced by low-temperature pyrolysis was examined under a 28-kWe high-flux solar simulator considering different operating conditions. The effects of CO2:C and feedstock mass on the key performance indicators e.g. the carbon conversion, energetic upgrade factor, and solar conversion efficiency were investigated by using alumina granules as an inert bed material. The first-hand, reproducible experimental data indicated the highest values of the average carbon conversion of 0.53 ± 0.04, energetic upgrade factor of 0.883 ± 0.03, solar conversion efficiency of 5.3 ± 0.6% were achieved under the operating conditions of 80 g charcoal, 1.5 kg alumina particles, and 2 L/min CO2. The feedstock mass significantly affected the solar conversion efficiency but no notable effect on the energetic upgrade factor was observed. The solar conversion efficiency can be significantly improved via fully replacing inert alumina particles by feedstock, adding a continuous feeder, and optimizing the superficial velocity to minimize particle entrainment.

Investigation of particles deposition in a square duct using optimized roughness elements for a sustainable environment

A sustainable environment is one of the major challenges in developing countries especially in populated regions due to the industrialization and expansion of urban areas. The industries emit particulate matter into the atmosphere that is harmful to human health. There is a need for an efficient particle separation mechanism to improve indoor air quality. This paper presents a numerical investigation of particles deposition in a square duct with variable roughness elements. The working fluid was taken as a mixture of air and inert particles. The Reynolds Stress Model (RSM) and Discrete Particle-phase Model (DPM) were used to simulate the particle-laden flow to analyze the deposition and velocity of the particles in the duct. The diameter of the particles is taken as 5 µm. The ratio of roughness height to the diameter ( r/ D) ranged from 0.024 and 0.101 and the spacing to the diameter ratio ( s/ D) varied between 9.8 and 39.23. It was found that the roughness height has a significant effect on the fluid flow as compared to the spacing between the elements. As a result, more uniform vortices are developed across the elements increasing fluid velocity from 10 to 14 m/s, while the deposition and velocity of the particles were increased by 14% and 8%, respectively. Accordingly, the particles deposition technique helps provide clean indoor air for better environmental sustainability.

Ignition Thresholds and Flame Propagation of Methane/Air Mixtures Ignited via Radiatively Heated Inert Particles

The prevention and evaluation of explosions requires suitable standards of measurement. As such, for this study two ignition thresholds, the ignition temperature and the minimum ignition irradiance were selected as the assessment criteria. These ignition threshold values were experimentally determined by heating stationary inert silicon carbide particles via thermal radiation with a large spot size in order to ignite quiescent methane-air fuel mixtures. A high-speed Schlieren camera was used to capture the progression of the formation and propagation of the flames throughout the experiments. The results of the experiments show that the irradiance and temperature threshold are directly and inversely proportional to the particle size, respectively. Furthermore, the irradiance and temperature thresholds have similar tendencies within the flammability limits; wherein, the minimum value corresponds to fuel mixtures at a stoichiometric ratio, and increases as the equivalence ratio shifts toward the flammability limits. Irradiance thresholds, though, are more sensitive to changes in equivalence ratio than temperature. The temperature histories of the heated particle determined that when the irradiance is lower than its ignition threshold value, the heated particle-fuel mixture system will arrive at a thermal equilibrium, rather than ignition, due to the inability of the particle to reach the ignition temperature. This study also found that longer ignition times will result in a more drastic deformation of the flame fronts caused by natural convection.

Enhanced Biomechanically Mediated "Phagocytosis" in Detached Tumor Cells.

Uptake of particles by cells involves various natural mechanisms that are essential for their biological functions. The same mechanisms are used in the engulfment of synthetic colloidal drug carriers, while the extent of the uptake affects the biological performance and selectivity. Thus far, little is known regarding the effect of external biomechanical stimuli on the capacity of the cells to uptake nano and micro carriers. This is relevant for anchorage-dependent cells that have detached from surfaces or for cells that travel in the body such as tumor cells, immune cells and various circulating stem cells. In this study, we hypothesize that cellular deformability is a crucial physical effector for the successful execution of the phagocytosis-like uptake in cancer cells. To test this assumption, we develop a well-controlled tunable method to compare the uptake of inert particles by cancer cells in adherent and non-adherent conditions. We introduce a self-designed 3D-printed apparatus, which enables constant stirring while facilitating a floating environment for cell incubation. We reveal a mechanically mediated phagocytosis-like behavior in various cancer cells, that was dramatically enhance in the detached cell state. Our findings emphasize the importance of including proper biomechanical cues to reliably mimic certain physiological scenarios. Beyond that, we offer a cost-effective accessible research tool to study mixed cultures for both adherent and non-adherent cells.

Mechanical and Chemical Interactions in Atomically Defined Contacts

AbstractProviding fundamental insights in atomic interactions, dedicated methods in atomic force microscopy allow measuring the threshold forces needed to move single adsorbed atoms or molecules. However, the chemical and structural properties of the probe‐tip can drastically influence the results. Establishing atomically defined contacts in such experiments, the tips in the present study are functionalized with various chemically and structurally different terminations. Xenon atoms are moved along an atomically defined metal/metal‐oxide boundary where all tips show a pulling mechanism and slight force variations, which are assigned to polarization effects within the tip‐sample junction. Detaching Xe atoms from the boundary involves a significantly higher energy barrier where chemical reactive Cu‐tips cause Xe pickup before any lateral manipulation. Passivating the tip by inert probe particles (Xe or CO) allows further approaching the surface Xe atom. Yet, the small vertical attraction and pronounced tip relaxations prevent reaching sufficient threshold forces inducing manipulation. In contrast, the high structural rigidity of oxygen‐terminated Cu‐tips allows manipulations even beyond the threshold where they evolve from initial pulling, via sliding to pushing mode. The detailed quantitative analysis of the processes in the atomically defined junctions emphasizes the mechanical and chemical interactions for highly controlled experiments with piconewton sensitivity.

Techno-Economic Analysis of Candidate Oxide Materials for Thermochemical Storage in Concentrating Solar Power Systems

The thermal storage capability is an important asset of state-of-the-art concentrating solar power plants. The use of thermochemical materials, such as redox oxides, for hybrid sensible/thermochemical storage in solar power plants offers the potential for higher specific volume and mass storage capacity and as a consequence reduced levelized cost of electricity making such plants more competitive. For the techno-economic system analysis, three candidate redox materials were analyzed for their cost reduction potential: cobalt-based, manganese–iron–based, and perovskite-based oxide materials. As a reference process the use of inert commercial bauxite particles (sensible-only storage) was considered. A solar thermal power plant with a nominal power of 125 MWe and a storage capacity of 12 h was assumed for the analysis. For each storage material a plant layout was made, taking the specific thermophysical properties of the material into account. Based on this layout a particle break-even cost for the specific material was determined, at which levelized cost of electricity parity is achieved with the reference system. Cost factors mainly influenced by the material selection are storage cost and steam generator cost. The particle transport system cost has only a minor impact. The results show differences in the characteristics of the materials, for example, regarding the impact on storage size and cost and the steam generator cost. Regarding the economic potential of the candidate redox materials, the perovskite-based particles promise to have advantages, as they might be produced from inexpensive raw materials.

Laboratory Investigation of Underground Fire Hazard Control in Coal Mines by Use of the Pyrotechnic Aerosol

ABSTRACT To control underground fire hazards, the principle of a pyrotechnic aerosol was adopted in coal fire-extinguishing experiments. Results show that fire extinguishing efficiency of a pyrotechnic aerosol composed of 63.4% KNO3, 23.6% C2H4N4, 8% C7H6O2, and 2% C8H5KO4 is better than that of nitrogen at 0.25 MPa. The required time to fire extinction is reduced by 41.6% in a 1 m3 control volume. TG/DTG tests support the view that the aerosol and its residues inhibit the oxidation and retards the combustion of coal. According to the EDS tests, the solid residues of the PA are mainly alkaline potassium salts such as K2CO3 and KHCO3. The FTIR results indicate that the K from the pyrotechnic aerosol will interact with the -OH in coal samples and also creates an alkaline environment inhibiting the production of -COOH. The effect on a pyrotechnic aerosol on coal fires is to produce ultra-fine and inert residue particles to extinguish the fire.

Pulmonary Drug Delivery of Antimicrobials and Anticancer Drugs Using Solid Dispersions.

It is well established that currently available inhaled drug formulations are associated with extremely low lung deposition. Currently available technologies alleviate this low deposition problem via mixing the drug with inert larger particles, such as lactose monohydrate. Those inert particles are retained in the inhalation device or impacted in the throat and swallowed, allowing the smaller drug particles to continue their journey towards the lungs. While this seems like a practical approach, in some formulations, the ratio between the carrier to drug particles can be as much as 30 to 1. This limitation becomes more critical when treating lung conditions that inherently require large doses of the drug, such as antibiotics and antivirals that treat lung infections and anticancer drugs. The focus of this review article is to review the recent advancements in carrier free technologies that are based on coamorphous solid dispersions and cocrystals that can improve flow properties, and help with delivering larger doses of the drug to the lungs.

Investigation into flow and heat transfer characteristics of sparse particles in beam fluidized bed receiver

In this paper, numerical simulation is carried out for the beam-type fluidized bed receiver. The mixture of air and inert particles is used as heat transfer medium in the simulation. Eulerian–Lagrange method and DO radiation model are used to describe the flow and heat transfer characteristics of gas and inert particles in fluidized bed receiver. At the same time, DPM method is used to consider the effect of particles on radiation field and the interaction between particles and flow field. Tracking particle wrapping and the temperature distribution, flow and heat transfer process of particles are analyzed. The particle temperature distribution is mainly concentrated in 550–800K, and 70% of the particles participate in effective heat transfer in terms of radial particle temperature and volume distribution. When the number of high temperature particles reaches 50%, the heat absorption capacity of mixed medium is optimal. At the same time, the fitting function with particle volume fraction as independent variable is obtained.

Analytical solution for unsteady adiabatic and isothermal flows behind the shock wave in a rotational axisymmetric mixture of perfect gas and small solid particles

Abstract The approximate analytical solutions are obtained for adiabatic and isothermal flows behind a cylindrical shock wave in a dusty gas. A mixture of perfect gas and micro size small inert solid particles is taken as the dusty gas. The inert solid particles are distributed continuously in the mixture. It is considered that the equilibrium flow conditions are maintained. The flow variables are expanded in power series to obtain the solution of the problem. The analytical solutions are obtained for the first order approximation in both the adiabatic and isothermal cases. Also, the system of ordinary differential equations for second order approximations to the solution is obtained. The influence of an increase in the ratio of the density of the inert solid particles to the initial density of the perfect gas, the rotational parameter and the mass concentration of inert solid particles in the mixture are discussed on the flow variables for first approximation. Our first approximation to the solution corresponds to the Taylor’s solution for the creation of a blast wave by a strong explosion. A comparison is also made between the solutions for isothermal and adiabatic flows. It is investigated that the density and pressure near the line of symmetry in the case of isothermal flow become zero and hence a vacuum is formed at the axis of symmetry when the flow is isothermal. Also, it is found that an increase in the value of rotational parameter or the mass concentration of solid particles in the mixture has a decaying effect on shock wave. The present work may be used to verify the correctness of the solution obtained by self-similarity and numerical methods.

Ignition of EPS foam by a hot moving hollow particle: Threshold, auto-ignition, and fire point

The ignition of building insulation materials by hot moving inert particles from fireworks display and welding processes is responsible for many tragic building fires. In this work, a hot hollow steel particle with various void ratio and diameter is dropped to ignite the low-density (16 kg/m3) expandable polystyrene (EPS) foam with three back boundary conditions. Results show that the minimum ignition temperature of hollow particles is close to solid particles (about 800 °C), and the temperature and size of particle are better measures of the spotting fire hazard than the particle mass and energy. As the void ratio increases, the minimum particle temperature for ignition first slightly decreases because the residence time of moving particle increases. For extremely hollow particles, ignition requires a much higher particle temperature to overcome the fast cooling. Besides the piloted ignition by hot particle, the auto-ignition phenomenon is observed for the first time, which is controlled by time scales of mixing and cooling. Moreover, the semi-open fuel back boundary shows the biggest fire hazard, because both good oxygen supply and long particle residence time promote the ignition to the fire point and fuel burnout. This study deepens the understanding of the complex interaction between hot porous particles and foam materials in the spotting ignition process of the building façade.

Load-flexible fixed-bed reactors by multi-period design optimization

Many research activities focus on load-flexible fixed-bed reactors in the context of Power-to-X concepts. One of the main issues is the occurrence of hazardous temperature excursions in steady state and during dynamic load changes. The dilution of the catalytically active fixed-bed with inert particles and the use of catalyst particles with active core and inert shell (so-called core–shell catalyst particles) are proven means to prevent insufficient thermal management. This work aims at comparing both concepts with respect to the reactor’s load-flexibility, exemplified for carbon dioxide methanation. In extension to our previous work of Zimmermann et al. (2020), a multi-period design optimization approach is performed for both concepts, considering one, two, and infinitely many axial fixed-bed segments. This approach simultaneously determines the optimal reactor design and operating parameters, which is inevitable for a sound technological comparison of the two concepts. Additionally, step responses are simulated as worst-case load change policy to switch from one optimized steady state to another. The results show that with core–shell particles shorter tubes can be used than with diluted fixed-beds, if one or two fixed-bed segments are considered. This results in lower pressure loss and higher space–time yield. Additionally, faster load changes can be realized with core–shell catalyst particles. In the case of infinitely many axial fixed-bed segments, both concepts converge to similar space–time yields, but show excessive temperature excursion during load changes.

Ultrasonic activation of inert poly(tetrafluoroethylene) enables piezocatalytic generation of reactive oxygen species

Controlled generation of reactive oxygen species (ROS) is essential in biological, chemical, and environmental fields, and piezoelectric catalysis is an emerging method to generate ROS, especially in sonodynamic therapy due to its high tissue penetrability, directed orientation, and ability to trigger in situ ROS generation. However, due to the low piezoelectric coefficient, and environmental safety and chemical stability concerns of current piezoelectric ROS catalysts, novel piezoelectric materials are urgently needed. Here, we demonstrate a method to induce polarization of inert poly(tetrafluoroethylene) (PTFE) particles (<d > ~ 1–5 μm) into piezoelectric electrets with a mild and convenient ultrasound process. Continued ultrasonic irradiation of the PTFE electrets generates ROS including hydroxyl radicals (•OH), superoxide (•O2−) and singlet oxygen (1O2) at rates significantly faster than previously reported piezoelectric catalysts. In summary, ultrasonic activation of inert PTFE particles is a simple method to induce permanent PTFE polarization and to piezocatalytically generate aqueous ROS that is desirable in a wide-range of applications from environmental pollution control to biomedical therapy.

Inhibition of temperature runaway phenomenon in the Sabatier process using bed dilution structure: LBM‐DEM simulation

AbstractThe Sabatier process is promising for carbon dioxide utilization and energy storage. However, the serious problem that limits more comprehensive industrial applications is catalyst deactivation due to the temperature runaway phenomenon. The inert particle dilution approach, including the mixing dilution method and layered dilution method is applied to solve this problem. Based on the lattice kinetic scheme‐lattice Boltzmann method (LKS‐LBM), the effects of three parameters in bed dilution structure reconstructed by the discrete element method (DEM) on temperature distribution and carbon conversion rate were discussed, so as to investigate the relationship between packing structure and temperature distribution. Furthermore, numerical results indicated that an optimal bed dilution structure, which not only can control the peak temperature below the critical temperature to avoid coking and sintering of catalyst, but also can improve the conversion rate by almost 18% compared with the structure without dilution under the same circumstance.

Modeling multiple anomalous diffusion behaviors on comb-like structures

In this work, a generalized comb model which includes the memory kernels and linear reactions with irreversible and reversible parts are introduced to describe complex anomalous diffusion behavior. The probability density function (PDF) and the mean squared displacement (MSD) are obtained by analytical methods. Three different physical models are studied according to different reaction processes. When no reactions take place, we extend the diffusion process in 1-D under stochastic resetting to the N-D comb-like structures with backbone resetting and global resetting by using physically derived memory kernels. We find that the two different resetting ways only affect the asymptotic behavior of MSD in the long time. For the irreversible reaction, we obtain memory kernels based on experimental evidence of the transport of inert particles in spiny dendrites and explore the front propagation of CaMKII along dendrites. The reversible reaction plays an important role in the intermediate time, but the asymptotic behavior of MSD is the same with that in case of no reaction terms. The proposed reaction-diffusion model on the comb structure provides a generalized method for further study of various anomalous diffusion problems.

Controlling glass bead surface functionality - Impact on network formation in natural edible polymer systems

Combining particles and polymers provides materials with unique mechanical properties. Hereby, the character of the particle surface is important for the network properties. However, particle-polymer interfaces of food systems are scarcely controllable. This often leads to an indefinite contribution on the network properties. Developing hybrid artificial systems by using inert particles with a well-defined coating represents a new approach in food science. Coating with functionalized silanes enables the imitation of naturally occurring chemical groups. A novel experimental approach involving nano- and macroscopic analytical techniques (X-ray photoelectron spectroscopy and contact angle) sheds light on the nature and the strength of the adsorption. Depending on the presented surface functionality, strong specific to weak unspecific adsorptions arise, e.g. amino-functionalized surfaces show strong interaction with protein, while almost no interaction was observed with an aliphatic surface. Based on these different particle adhesivenesses, the monitoring of network formation discloses a significant impact of particle surface functionality on network development of food matrixes. An increasing network development time (3.2–6.0 min, gluten protein-based) in combination with a decreasing network strength (874-464 mNm gluten protein-based) correlates with an increasing adhesiveness of particles. Thus, using functionalized particles clearly demonstrates the importance of particle surface functionality on network properties in food systems.

The heating of a stream of particles by thermal counter radiation

Introduction. It is accepted that the depth of heating of the dust/gas/air mixture by the radiation of combustion products SR is equal to the length LR of the free path of radiation in the mixture. Numerical simulation of combustion of a gas-air mixture that has inert particles, taking into account the re-radiation of heat by heated particles of the fresh mixture, led to ratio SR &gt;&gt; LR. In this work, the analytical assessment of ratio χS = SR/LR is performed.One-dimensional problem model. The co-authors determined stationary temperature distribution over the flow of initially cold monodisperse particles suspended in vacuum. Particle velocity V is directed toward a heat-radiating, absolutely black surface that is permeable by particles. Simplifying assumptions are used: radiation consists of two oppositely-directed flows of electromagnetic energy; interaction between particles and radiation is described in the approximation of geometric optics; the temperature inside the particle is the same. Problem solving. It is shown that χS is determined by V=Vcp / (εT 0,5, σTb)3 , where cp, εT, σ, Tb are, respectively, heat capacity per unit volume of the suspended matter, integral emissivity of the particle material, the Stefan-Boltzmann constant, and the surface temperature. For ≤ 2.8, re-emission can be neglected: χS ≈ 1. At ≤ 1.2, temperature distribution regulates re-emission: χS ≈ 5 –1/(2 – εT) &gt;&gt; 1.Solution discussion. The analytical solution satisfactorily describes the available numerical solutions and experimental data for the case of combustion of a dust/gas/air mixture after specifying the parameters of a simplified model: the radiating surface should be understood as the flame front, Tb is the combustion temperature, and cp is the overall heat capacity of the mixture. The estimate ≤ 1.2 indicates the final high temperature of the gas suspension, the possibility of its autoignition far from the flame, and the need to change initial assumptions when simulating re-emission.Conclusions. Analytical evaluations make it possible to employ ratios SR &gt;&gt; LR and SR ≈ LR for the suspension over a thermal radiation source in vacuum. Conditions for the application of the results of simplified simulation of re-emission to the combustion of a dust/gas/air mixture are formulated.

Dose fractionation as a promising strategy to improve UV disinfection

Survival curves for bacteria exposed to germicidal radiation (254 nm) usually exhibit a decreased slope at high doses, because bacterial populations contain a small proportion of cells able to tolerate the effects of the radiation. These cells could survive due to external shielding by aggregation or association with inert particles. However, it has been proposed that transient and reversible phenotypic changes modifying UV susceptibility also occur and lead to a phenomenon of persistence. Using Escherichia coli as a model organism, and comparing the effects of continuous exposures to those of irradiations separated by incubations in the dark, we found that in most of the survivors to high UV doses, the condition conferring tolerance (possibly self-aggregation) is transient and reversible, as would be expected in a persistent sub-population. Splitting the irradiations into two exposures reduced viable counts to the detection limit (6.32 orders of magnitude) under conditions in which continuous irradiations produced a reduction no greater than 4 orders of magnitude. In those processes where it is feasible, UV dose fractionation could improve the effectiveness of disinfection by ultraviolet radiation.