Mixture Of Solid Particles Research Articles

Studies and Research Concerning the Displacement of Solid Particle on an Oscillatory Flat Surface

The article shows how the operating parameters of a machine used for the separation of a heterogeneous mixture of solid particles affect particle residence time on the working surface in use, the distance followed, respectively the travel speed. Experimental determinations were performed in the laboratory on a stand which working surface runs an alternative oscillatory motion. In the experimental measurements there have been used real particles, respectively small grain beans. Stand parameters which were considered were the angle of the swing plane surface (5o, 7o and 10o) and the crank speed (91, 240 and 405 rpm). As a result of the analysis it was found that between the functional parameters of the working stand (the distance travelled by the particle oscillating solid surface, the time in which the particle follows the distance used as a reference, the linear velocity of the solid particles on the travelled distance) are closely related.

Erosion predictions of stock pump impellers based on liquid-solid two-phase fluid simulations

Stock pumps cost 25 percent of total power consumption in a modern paper mill. Owing to the severe erosion of pump casing and impeller during operation, stock pump often results in efficiency drop and rising power consumption. A favourable prediction of the impeller wearing character can effective guide optimization design of stock pump impeller. Thereby it can reduce impeller wear and extend stock pump performance life. We simulated the three-dimensional unsteady solid-liquid two-phase flow characteristic in the hydraulic channel of a low specific speed stock pump with open and three blades impeller. The standard k- ε turbulent model and the pseudo-fluid model were adopted in simulation. Clearance between covers and impeller is taken into consideration in modelling, and pulp is simplified into mixtures of solid particles and water. The Finnie prediction model is applied to predict impeller erosion character. The simulation results of different solid particle size are compared with practical impeller erosion character, and the effects of solid particle size on impeller erosion character are obtained. Thus, numerical method to simulate impeller erosion characteristics of fibered pulp is investigated.

Numerical simulation of 3D sloshing in a liquid–solid mixture using particle methods

SUMMARYSloshing of liquid–solid particle mixtures is an important issue in industrial settings and research fields. In numerical simulations, difficulties are encountered in capturing or tracking the interface between different phases and calculating the interactions between particles, as well as considering hydrodynamic effects between liquid and particles. The finite volume particle (FVP) method, which is based on the Lagrangian framework, does not require applying extra techniques to capture the dynamics at the interface. Moreover, the hydrodynamic behavior between liquid phase and solid particles can be solved implicitly. The discrete element method (DEM) is a useful computational tool, which can explicitly calculate the interaction forces acting on particles and exactly describe their transient trajectories. Owing to the same particle assumption and Lagrangian description, the approach coupling FVP and DEM is more straightforward than the Euler–Lagrange approach. In this study, the applicability of the coupled FVP/DEM method is investigated by simulating sloshing in liquid–solid particle mixtures. A comparison of simulation and experimental results shows good agreement and demonstrates the accuracy of the method. It is hoped that the FVP/DEM method can provide an effective 3D means for a quantitative comparison and validation of more complicated multiphase flows with a variety of particles. Copyright © 2013 John Wiley & Sons, Ltd.

Dynamics of dense granular flows of small-and-large-grain mixtures in an ambient fluid

Dense grain flows in nature consist of a mixture of solid constituents that are immersed in an ambient fluid. In order to obtain a good representation of these flows, the interaction mechanisms between the different constituents of the mixture should be considered. In this article, we study the dynamics of a dense granular flow composed of a binary mixture of small and large grains immersed in an ambient fluid. In this context, we extend the two-phase approach proposed by Meruane et al. [J. Fluid Mech. 648, 381 (2010)] to the case of flowing dense binary mixtures of solid particles, by including in the momentum equations a constitutive relation that describes the interaction mechanisms between the solid constituents in a dense regime. These coupled equations are solved numerically and validated by comparing the numerical results with experimental measurements of the front speed of gravitational granular flows resulting from the collapse, in ambient air or water, of two-dimensional granular columns that consisted of mixtures of small and large spherical particles of equal mass density. Our results suggest that the model equations include the essential features that describe the dynamics of grains flows of binary mixtures in an ambient fluid. In particular, it is shown that segregation of small and large grains can increase the front speed because of the volumetric expansion of the flow. This increase in flow speed is damped by the interaction forces with the ambient fluid, and this behavior is more pronounced in water than in air.

Dynamics in the boundary layer of a flat particle

The paper presents a theoretical study of the source of the spinning movement of the solid particles flowing in a moving fluid and the influence of the resulting Magnus force on the particles' trajectories along the stream lines, based on interactions occurring in the boundary layers. The subject is important for technological applications, like aerodynamic separation process of a mixture of solid particles. First, it is shown that the boundary layer equations generate local soliton-type, kink-type and soliton-kink-type nonlinear solutions for the velocity field. Using Prandtl's equations for boundary layer, nonlinear solutions of the velocity field are obtained. It was found that through the interaction on the boundary layers, the transition from the movement on continuous and differentiable curves (stream lines) to the movement on continuous and non-differentiable curves (fractal curves) occurs. This last characteristic can be used in the separation process of the solid components from a heterogeneous mixture.

Experimental investigation of solid–liquid mixtures freezing behavior in flow channels

The penetration and freezing of hot-core material mixtures through flow channels during core disruptive accidents (CDAs) within a sodium-cooled fast reactor is one of the major concerns confronting safety designers of the next-generation reactors. The main objective of this study is to investigate those fundamental characteristics of penetration and solidification involved in channeling molten metal and solid particle mixtures over cold structures. In this study, a low-melting-point alloy ( viz., Bi–Sn–In alloy) and mixtures with solid particles (of copper and bronze) were used as a simulant melt, while L-shape metal (of stainless steel and brass) and stainless steel fuel pin bundle were used as cooling structures. Two series of basic experiments were performed to study the effect solid particles have on penetration and cooling behavior under various thermal conditions of melt by varying solid particle volume fraction, structure temperature and structural geometry. Melt flows and distributions were recorded using a digital video camera and subsequently analyzed. The melt penetration length into the flow channel and the proportion of melt adhesion on structural surfaces were measured. Results indicate that penetration length becomes shorter for molten-metal/solid particle mixtures (mixed melts) compared with pure molten metal (pure melt) as well as decreases with increasing solid particles volume fraction of the melt. The present study will contribute to a better understanding of the basic thermal-hydraulic phenomena of melt freezing in the presence of solid particles and to provide an experimental database for validation and improvement of the models of fast reactor safety analysis codes.

Influence of surfactant structure on the double inversion of emulsions in the presence of nanoparticles

The double inversion of emulsions from oil-in-water (o/w) to water-in-oil (w/o) and back to o/w is a novel approach developed using oppositely charged mixtures of solid particles and surfactant molecules [B.P. Binks, J.A. Rodrigues, Angew. Chem. Int. Ed. 46 (2007) 5389]. This work extends these preliminary results reported for the cationic surfactant di-decyldimethylammonium bromide (di-C 10DMAB), by studying the influence of surfactant chain length for symmetrical cationic surfactants. Two double-chain surfactants with hydrocarbon chain lengths of 8 or 12 are used here to stabilise emulsions with dodecane in the presence of silica nanoparticles (Ludox HS-30). Double inversion of emulsions is also possible with these surfactants. However, multiple emulsions of both types are observed when the most hydrophobic surfactant di-C 12DMAB is used, occurring near the boundaries of the first and second inversion, respectively. A phase diagram is introduced, in which the double inversion of emulsions occurs at various particle-to-surfactant ratios, in particular at low concentrations of silica particles between 0.1 and 4 wt.%.

Hygroscopic Growth of Multicomponent Aerosol Particles Influenced by Several Cycles of Relative Humidity

Infrared aerosol flow tube experiments were performed for mixtures of ammonium, sulfate, and hydrogen ions at 293 K. The impact of the cycling of relative humidity (RH) on the crystals formed and on the hygroscopic growth was evaluated. Submicron particles having an extent of neutralization (X) between 0.60 and 0.75 were the focus, with special emphasis on the composition of aqueous letovicite (NH4)3H(SO4)2 (X = 0.75) because of its unique behavior. Aqueous letovicite particles crystallized initially as an external mixture of solid particles, forming pure particles of letovicite (NH4)3H(SO4)2(s) (LET) in some cases and internally mixed particles of ammonium sulfate ((NH4)2SO4(s);AS) and ammonium bisulfate (NH4HSO4(s); AHS) in other cases. Cycling between 3% and 48% RH increased the fraction of LET particles in the aerosol population, moving in the direction of the more thermodynamically favored species. However, some internally mixed particles remained even after multiple cycles, possibly indicative of a memory effect of AS as a heterogeneous nucleus for AHS. For all compositions studied, the RH of first water uptake and the magnitude of water uptake at higher RH were compared to model predictions. As expected, the more acidic particles (X = 0.60 and 0.65) took up water at the eutonic RH (37%) of mixed AHS/LET particles, but not as expected, both solids dissolved completely, arguing for an increased water solubility possibly attributable to nanocrystalline materials. Particles of X = 0.70 took up water above 41% RH, suggesting a particle morphology of an outer coating of AHS that prevents water uptake at the lower eutonic RH values of mixed AHS/LET and AHS/AS particles. Particles of X = 0.75 took up water as expected for an externally mixed particle population of LET and AS/AHS particles, although the fraction of each type in the population depended on the RH history. These results show that the hysteresis effect for some particles depends on a multi-node RH history. The implication for atmospheric particles is that the crystals present therein as well as particle morphology, water content, and extent of internal/external mixing might continue to evolve during multiple atmospheric cycles of RH.

Calculation of the hindered settling velocity of a bimodal mixture of solid particles of arbitrary shape in a Newtonian fluid

A method for calculating the settling velocity of a bimodal mixture of particles of arbitrary shape is proposed. The method uses the concept of effective particle diameter, which characterizes the particle shape, volume, and midsection area. The method takes into account the contact interaction between particles of different sizes due to their collisions. The calculation results are compared with experimental data on settling of bimodal mixtures of limestone particles of arbitrary shape.

Simultaneous lidar observations of a polar stratospheric cloud on the east and west sides of the Scandinavian mountains and microphysical box model simulations

Abstract. The importance of polar stratospheric clouds (PSC) for polar ozone depletion is well established. Lidar experiments are well suited to observe and classify polar stratospheric clouds. On 5 January 2005 a PSC was observed simultaneously on the east and west sides of the Scandinavian mountains by ground-based lidars. This cloud was composed of liquid particles with a mixture of solid particles in the upper part of the cloud. Multi-colour measurements revealed that the liquid particles had a mode radius of r≈300 nm, a distribution width of σ≈1.04 and an altitude dependent number density of N≈2–20 cm−3. Simulations with a microphysical box model show that the cloud had formed about 20 h before observation. High HNO3 concentrations in the PSC of 40–50 weight percent were simulated in the altitude regions where the liquid particles were observed, while this concentration was reduced to about 10 weight percent in that part of the cloud where a mixture between solid and liquid particles was observed by the lidar. The model simulations also revealed a very narrow particle size distribution with values similar to the lidar observations. Below and above the cloud almost no HNO3 uptake was simulated. Although the PSC shows distinct wave signatures, no gravity wave activity was observed in the temperature profiles measured by the lidars and meteorological analyses support this observation. The observed cloud must have formed in a wave field above Iceland about 20 h prior to the measurements and the cloud wave pattern was advected by the background wind to Scandinavia. In this wave field above Iceland temperatures potentially dropped below the ice formation temperature, so that ice clouds may have formed which can act as condensation nuclei for the nitric acid trihydrate (NAT) particles observed at the cloud top above Esrange.

Gravel Packing Long Horizontal Wells With Low Fracture Gradients

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 96396, "The Dynamic Bottomhole Pressure Management: A Necessity to Gravel Packing Long Horizontal Wells With Low Fracture Gradients," by Z. Chen, SPE, and R.J. Novotny, SPE, BJ Services Co., prepared for the 2005 SPE Annual Technical Conference and Exhibition, Dallas, 9–12 October. Unconsolidated formations are commonly found in offshore reservoirs where long and ultralong horizontal wells are required to produce heavy oil economically. Gravel packing is an efficient and cost-effective sand-control practice for these high-permeability, large-porosity, low-fracture-gradient formations. Successful placement of the gravel-pack completion requires that these low-fracture-gradient wells not be fractured during gravel placement. A dynamic-pressure-management scheme is critical to maintain bottomhole pressures (BHPs) in the required range. Introduction Horizontal-well openhole screen completions have been performed for years and offer many advantages. These advantages can be offset quickly by failure if the job is not carefully designed and executed. This is especially the case for wells with long and ultralong horizontal wellbore sections in unconsolidated formations with low fracture gradients. Although horizontal openhole gravel-pack completions have continued to gain acceptance as reliable completion techniques, they are still under development and often encounter new challenges. In some cases, there may not be any safe operational windows under conventional operation procedures. Dynamic BHP Management During gravel placement in horizontal wells, BHP must be monitored constantly to avoid fracturing the formation. Any excessive leakoff will cause a screenout and, thus, an incomplete sand-control completion. To ensure a successful packing job, an effective BHP-management scheme needs to consider both job-design time and actual job execution. Gravel-Packing Model The gravel-packing physical phenomenon in a horizontal well can be described as alpha-/beta-wave packing. Several flow patterns can be encountered in a given section, affecting the pressure-gradient/flow-rate relation. During alpha-/beta-wave packing, a stationary bed is created at the bottom of the flow path and a heterogeneous mixture of solid particles and carrier fluid flows through the upper part (Fig. 1). The stationary bed at the bottom of the flow path builds up and grows forward like a wave; it is from this that the expression "alpha wave" is derived. The flow path or void above the alpha wave will be packed after the alpha wave packs forward to the bottom of the screen. In the alpha-/beta-wave model, it is assumed that the space above the alpha wave will be packed backward to the top of the screen. The packing process during this phase exhibits a pistonlike movement, packing all the space backward, and is named the beta wave (Fig. 2).

Feinstaub(PM10)- und Pollenbelastung im Winter und ihre Abhängigkeit von der Wetterlage

Particulate matter (PM) is the general term used for a mixture of solid particles and liquid droplets found in the air. These particles, which come in a wide range of sizes (fine particles are less than 2.5 μm in diameter and coarser-size particles are larger than 2.5 μm), originating from many different stationary and mobile sources as well as from natural sources. Fine particles result from fuel combustion from motor vehicles, power generation and industrial facilities as well as from residential fireplaces and wood stoves. Coarse particles (PM10) are generally emitted from sources, such as vehicles traveling on unpaved roads, materials handling and crushing and grinding operations, as well as windblown dust. Inhalable PM includes both fine and coarse particles. These particles can accumulate in the respiratory system and are associated with numerous health effects. Exposure to coarse particles is primarily associated with the aggravation of respiratory conditions, such as asthma. Fine particles are most closely associated with such health effects like increased hospital admissions and emergency room visits for heart and lung disease, increased respiratory symptoms and disease, decreased lung function, and even premature death. Sensitive groups that appear to be at greatest risk to such effects include the elderly, individuals with cardiopulmonary disease such as asthma, and children. This study investigates PM10 and airborne pollen during different years and shows connections between weather conditions in winter time and these particles.

Hindered settling velocity of a bimodal mixture of spherical solid particles in a Newtonian fluid

Works describing methods for calculating the settling velocity of a biomodal mixture of solid particles are analyzed. A method for calculating the settling velocity of a bimodal mixture of spherical particles is proposed that takes into account the contact interaction between particles of different sizes due to their collisions. The calculation results are in satisfactory agreement with experimental data on settling of a bimodal mixture of spherical solid particles.

Extraction of biologic particles by pumping effect in a π-shaped ultrasonic actuator

This paper presents a new method of extracting biologic particles from a mixture of particles. The method is based on the pumping effect in a π-shaped ultrasonic actuator, which has a gap between its two vibrating metal plates. An adhesive tape is placed at a proper position in the gap. Due to the pumping effect which is induced by the sound field in the gap, the particles with smaller mass and radius in the mixture can be pumped up to reach the adhesive tape; while the ones with larger mass cannot. Therefore, the particles with smaller mass and radius can be extracted from the mixture. A theoretical model which can well explain the operation principle and experimental phenomena is developed. By the experimental results and the theoretical analyses based on the model, the validity of the method in extracting small particles from a mixture of solid particles in air is confirmed, and the effects of the actuator’s vibration, adhesive tape height, contents of the mixture and viscosity of fluid on the extraction are clarified. Also, it is theoretically predicted that the method will work under the microgravity condition in air.

Reologia de suspensões minerais: uma revisão

Durante as etapas de processamento mineral, na maioria dos casos, há o envolvimento de suspensões - misturas de minério fino com uma fase líquida. Logo, as operações de processo são influenciadas pela resistência dessas suspensões em se deformar ou fluir, quando submetidas a forças de cisalhamento ou pressão, ou seja, a viscosidade da suspensão influenciará nas etapas de processamento. Nesse trabalho, será feita uma revisão sobre reologia de suspensões e o processamento mineral. Serão abordados aspectos conceituais sobre reologia de suspensão e suas variáveis, classificação reológica dos fluidos e determinações de viscosidade através do viscosímetro rotacional de cilindro concêntrico.

A spatial cluster method supported by GIS for urban-suburban-rural classification

This study was undertaken to construct a preliminary spatial analysis method for building an urban-suburban-rural category in the specific sample area of central California and providing distribution characteristics in each category, based on which, some further studies such as regional manners of residential wood burning emission (PM2.5, the term used for a mixture of solid particles and liquid droplets found in the air, refers to particulate matter that is 2.5µ m or smaller in size) could be carried out for the project of residential wood combustion. Demographic and infrastructure data with spatial characteristics were processed by integrating both Geographic Information System (GIS) and statistics method (Cluster Analysis), and then output to a category map as the result. It approached the quantitative and multi-variables description on the major characteristics variations among the urban, suburban and rural; and perfected the TIGER’s urban-rural classification scheme by adding suburban category. Based on the free public GIS data, the spatial analysis method provides an easy and ideal tool for geographic researchers, environmental planners, urban/regional planners and administrators to delineate different categories of regional function on the specific locations and dig out spatial distribution information they wanted. Furthermore, it allows for future adjustment on some parameters as the spatial analysis method is implemented in the different regions or various eco-social models.

Melting and coarsening of A356 during preheating for semisolid forming

The melting and coarsening behaviour of A356 during preheating for semisolid forming has been investigated theoretically and experimentally. The preheating involves a relatively rapid heating and a partial melting, transforming the material into a mushy state, i.e.a mixture of solid particles and melt. The experiments reveal a change in melting behaviour over the temperature interval 580–590°C, where a re-solidification occurs during heating. During the initial phase of melting, the smallest solid particles melt completely and larger particles are split into smaller particles, making the shape of the particles more irregular. Particle fragmentation influences the occurrence of the enclosed eutectic, which temporarily maintains a higher solid fraction as a result of increased diffusion distances. Resolidification and coarsening contribute to a rapid particle size increase. The model derived fits the experimental series well and supports the coarsening and particle fragmentation observations.

Mathematical model and numerical simulation of the liquid fluidization of polydisperse solid particle mixtures

Mathematical model and numerical simulation of the liquid fluidization of polydisperse solid particle mixtures

Mathematical model and numerical simulation of the liquid fluidization of polydisperse solid particle mixtures

A mathematical model for the fluidization of polydisperse suspensions is developed. The stationary concentration configurations for a given fluidizing velocity are analyzed and a mixing condition for bed inversion is derived. A central finite difference scheme is applied to the simulation of the fluidization of a bidisperse suspension. The numerical simulations agree with the experimentally reported qualitative behaviour of fluidized suspensions such as bed expansion and bed inversion.

Boundary Elernent Method Numerical Model Based On MixtureTheory Of Two-phase Flow

A boundary element numerical scheme for a flowing mixture of solid particles and a fluid is developed within the context of mixture theory. Major differences between the two in literature on the subject are studied, these are typically employed theories called the averaging approach and mixture theory. A numerical technique applied is the boundary element method based on velocityvorticity formulation of general equations describing the flow of a twocomponent mixture of a Newtonian fluid and a granular solid. Integral representations for conservation and field functions, based on parabolic diffusion fundamental solution, are presented. Special attention is focused on the mechanical interaction between the mixture components.