Segregation Of Mixtures Research Articles

Inhomogeneous Segregation of Binary Mixtures in Fluidized Beds

This paper deals with segregation effects in of binary mixtures in a 2D fluidized bed. In the experiment initial inhomogeneities in the particle mixture lead to uneven bed pressure drop. This results in inhomogeneous particle segregation and the formation of heap like structures. The effect is clearly reproducible for small particle mass fractions of 40 to 60%. A numerical model based on a hybrid DPM/Euler model was developed and shows a similar behaviour for initial disturbances in the binary particle mixture.

DEM investigation of granular flow and binary mixture segregation in a rotating tumbler: Influence of particle shape and internal baffles

DEM investigation of granular flow and binary mixture segregation in a rotating tumbler: Influence of particle shape and internal baffles

The Study Summery of Segregation Characters for Asphalt Mixture Based on Discrete Element Method

This paper summarizes the characteristics of the relevant theory research of asphalt mixture segregation at home and abroad in recent years, the use of discrete element methods, by summing up the results of different studies scholars, analysis of discrete element method to simulate Evaluation of asphalt mixture segregation as well as its advantages and disadvantages, numerical simulation to explore the direction of development.

Dynamical effects in the segregation of granular mixtures in quasi 2D piles

The dynamics of segregation, mixing and layering is studied during the build-up of quasi-2D piles of two different species of grains of different diameters (i.e. 1mm glass beads and either 3mm glass beads or 3.1mm coriander seeds). The ranges of existence of the different flow regimes are studied as a function of the relative volume flow rates of the two species and of the drop height; the variation of the mean slope of the pile with time is shown to depend on the flow regime. Complete segregation occurs when the larger grains are coriander seeds while there is always some mixing for glass beads, although the ratio between the sizes of the particles is the same in both cases. A layered regime is observed for glass beads of same geometry (i.e. spheres) and density but of two different diameters: it is accompanied by variations of large amplitude of the slope of the pile. No layering occurs when the large particles are coriander seeds instead of glass beads. The local processes underlying these regimes are analyzed quantitatively from spatiotemporal diagrams of the profile of the free surface and the characteristic velocities of the different types of displacements of the grains are determined. Avalanches are only observed for glass beads and in the layered regime and play an important part in the development of the layers.

The Base Material Segregation Control Technology Research of Strong Interlocked Skeleton Dense Graded Aggregate

Compared with the traditional framework dense structure, strong embedded squeeze skeleton dense cement stabilized crushed stone has a stronger embedded squeeze force, the more excellent mechanical properties.This article briefly describes strong embedded squeeze the skeleton dense cement stabilized crushed stone grading design and mechanical properties, and strong embedded squeeze Framework Grading cement stabilized crushed stone in the construction of many materials Segregation. Through the experimental contrast research with traditional construction method, the new method almost eliminate the problems of mixture segregation, which can be used for reference in construction application.

Effects of processing additive on bipolar field-effect transistors based on blends of poly(3-hexylthiophene) and fullerene bearing long alkyl tails

Bipolar FETs (BiFETs) based on the bulk heterojunction system comprised of various ratios of P3HT and soluble fullerene derivatives are demonstrated. We studied the effect of addition of small concentrations of the processing additive, 1,8-octanedithiol (ODT), on gate-induced transport properties. The control blend system consisting of poly (3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) showed enhanced hole transport properties with the addition of the ODT additive. However, electron transport properties were diminished in the presence of ODT additive because of the relatively isolated PCBM phase between the large-scale segregation of the P3HT amorphous phase. The BHJ BiFET based on P3HT and soluble fullerene derivatives bearing long alkyl tails (FP-Ph-OC10) showed enhanced performance in both hole and electron transport when the ODT additive was applied. We attribute the enhancement of hole mobility to well-formed P3HT fibrilla structures of P3HT caused by the alkyl–alkyl interaction assisted by both the ODT additive and alkyl side chain in FP-Ph-OC10. As the P3HT forms fibrilla structures, connection to the isolated FP-Ph-OC10 phase be formed, resulting in a continuous electron pathway, thereby improving electron mobility. This suggests that not only the selective solubility, but also the alkyl-alkyl interaction between the side-chain and ODT additive may affect the phase segregation of BHJ mixtures.

A Method to Evaluate Mixture Segregation Based on Space Grid of Image Processing Technology

A space grid method, based on image processing technology, was proposed to evaluate asphalt mixture segregation, which used the ratio of statistical data variance and its square of mathematical expectation to describe material uniformity by statistics of distribution of particles on space grid. Computer procedure was developed and some experiments are made. The results indicate that this method is simple and can be used to evaluate asphalt mixture uniformity quantitatively with a good adaptability.

Experimental Evidence of Mixture Segregation by Particle Size Distribution

In this study, we discuss experimental segregation results obtained for two industrial cases, namely, ammonium perchlorate and a polymeric resin. These results show a segregation effect due to particle size distribution rather than particle size itself. We used a heap-pouring device as a tester, for which a visual knowledge of the segregation state was observed. The analysis of segregation is based on various coefficients of variations related to the size fractions or particle size distribution's global characteristics, indicating heterogeneities in the heaps formed. Both cases indicate that wide particle size distributions, as opposed to narrow ones, are limiting segregation risks. This collective, and maybe astonishing, effect is extremely marked for the cases studied, and demonstrates again the mesoscopic nature of granular media.

Radial segregation of multi-component granular media in a rotating tumbler

Segregation and mixing of granular mixtures are important to the minerals, food processing and pharmaceuticals industry to name just a few. It has recently been demonstrated that a rotating tumbler is a suitable device for separating out binary granular mixtures, i.e. mixtures composed of only two different particle types. However, most practical granular mixtures are composed of multi-component particle types. We therefore study the capability of this rotating tumbler to segregate mixtures composed of more than two components where the particles differ either in size or density. The general pattern of segregation involves the formation of an inner core of smallest or densest particles followed, at larger radii, by the next largest or densest particle type and so-on in an onion-like pattern. In the mixtures where particles differ in size we always get relatively pure inner cores of the smallest particles, while the other regions are less segregated. On the other hand for mixtures whose particles differ in density we get a relatively pure outer region (adjacent to cylinder wall) consisting of the least dense particles while the other regions are less segregated. We attempt to relate the simulation results to phenomenological theory and find that size segregation in a specific multi-component mixture can be suitably described by a recent theoretical model.

Methods for Reducing Energy Consumption and Carbon Emission in Asphalt Pavement Construction

In the construction process of asphalt pavement, mixing is the process which brings most of carbon emission. There is huge potential advancement of energy conservation, emission reduction and consumption reduction in the construction of asphalt pavement. Research on the structure improvement of construction equipment, the optimizing of the construction technological process and the influence of mixture performance and parameters is necessary. It is feasible to conduct interdisciplinary research in the condition that construction quality is ensured. There needs excellent control technology on efficient paving, efficient compaction and appropriate equipment match and temperature segregation of mixture. By doing this, the purpose of energy conservation and emission reduction in the construction process of hot-mix asphalt mixture can be achieved.

Quality control/quality assurance testing for longitudinal joint density and segregation of asphalt mixtures

Longitudinal joint quality control/assurance is essential to the successful performance of asphalt pavement and it has received considerable amount of attention in recent years. Five paving projects were selected for sampling and evaluation in Iowa. For each project, joint quality is compared with regard to the “center” of the pavement mat (6′ right of joint). Field densities and permeability test were made. Cores were obtained for subsequent lab permeability, density and indirect tensile (IDT) strength testing. Asphalt content and gradations were also obtained to determine the joint segregation.In general, this study found that methods providing the most reliable measurements of joint quality are the AASHTO T166, AASHTO T331 (CoreLok) density tests and the permeability test by Karol-Warner Permeameter. The minimum required joint density for quality control should be around 90.0% and 88.5% of theoretical maximum density based on the AASHTO T166 and AASHTO T331 method respectively. Based on various mix design and longitudinal joint construction methods, the joints show differences in asphalt content and level of segregation. Results of this study indicate that poor quality of longitudinal joint should be a combination of segregation, asphalt content variation and insufficient density.

Simulation of motion of particles in reciprocating grates using DEM

Abstract Motion of monosize particles and binary mixture in the reciprocating grate is simulated by means of Discrete Element Method (DEM). The flow behavior of monosize particles and the mixing and segregation processes of binary mixture with identical densities but different sizes subjected to horizontal reciprocating grates are investigated in this study. The spatial distributions of velocity and volume fraction of particles are predicted. The contact force and granular temperature of particles are calculated in a reciprocating grate. The mechanism causing the mixing and segregation of binary mixture is strongly dependent on the momentum exchange of each species which is related to the granular temperature of mixture components. The simulation results show that the translational granular temperatures of small particles are higher than those of large particles, indicating that the translational granular temperatures do not equilibrate for the binary mixture system. The kinetic energy of large particles is higher than that of small particles. The influence of amplitude and frequency on motion of particles is analyzed.

Segregation in mixtures of granular chains and spherical grains under vertical vibration

We experimentally investigate segregation behaviors of binary granular mixtures consisting of granular chains and spherical grains with different interstitial media under vertical vibrations. A quantitative criterion is proposed to locate the boundaries between different vibrating phases. The water-immersed granular mixture exhibits two interesting types of segregation behaviors: chain-on-top and sandwich patterns. However, the phenomenon of sandwich segregation is absent for the air-immersed mixture. The topological differences of phase diagrams between two different environments indicate that the interstitial fluid plays an important role on the granular demixing. Additionally, the phase behaviors of mixtures for the different chain lengths show a not significant discrepancy. Finally, the vibrating thickness ratio determining the phase boundary characterizes the mixing extent of the granular bed. The estimated ratios for various chain lengths exhibit a monotonically decreasing dependence, when the vibration frequency increases.

Spin Brazil-nut effect and its reverse in a rotating double-walled drum

The segregation of binary mixtures in a filled rotating double-walled drum is explored by simulations. Based on the characteristics of self-gravity and the centrifugal force, we argue that both percolation and buoyancy effects dominate the segregation process. The simulational results show that up to long enough times the segregation state is controlled by the rotational speed, the particle radius and density. At low rotational speeds, the smaller and heavier particles tend to accumulate towards the inner drum wall and the bigger and lighter ones towards the outer drum wall, while the segregation pattern reverses completely at higher rotational speeds. Two typical phase diagrams in the space of the density and radius ratio of bigger particles to smaller particles further confirm the predictions.

Mixing and segregation of binary oxygen carrier mixtures in a cold flow model of a chemical looping combustor

In a typical chemical looping combustion process, the oxygen for fuel combustion is supplied by circulating metal based oxygen carriers between two interconnected fluidised bed reactors. The redox characteristics of oxygen carriers and hence the overall performance of the process can be significantly improved by utilising binary mixtures of oxygen carrier particles. The full potential of such multi-species particle systems however can be only realised when particles segregation is minimised. This study is concerned with gaining an understanding of the mixing and segregation behaviour of binary mixtures of oxygen carrier particles with different sizes and densities in a cold flow model representing a 10kWth chemical looping combustor. The hydrodynamics of such systems were investigated and compared with a typical chemical looping combustion process where single species are used. This was followed by investigating the solids mixing and segregation behaviour in terms of segregation intensity and species weight percentage at each reactor as a function of operating parameters. It was shown that increasing the total solid inventory, particle terminal velocity ratio, composition, and air reactor superficial velocity increases the riser pressure, solid circulation rates, and riser solid holdup. Mixing and segregation regimes of the fuel reactor and the component segregation between the two reactors were also mapped. The results showed that, for mixtures of species with low terminal velocity to high terminal velocity ratios of greater than 0.7, a good mixing in the fuel reactor can be achieved by maintaining the superficial gas velocity to the mixture minimum fluidisation velocity ratio above 5. For the tested conditions, the component segregation between the two reactors was avoided by maintaining the ratio of the riser superficial velocity to the terminal velocity of the species with a high terminal velocity between 1.25 and 2.

The effect of liquids on radial segregation of granular mixtures in rotating drums

The presence of liquids can significantly affect the dynamics of granular flow. This paper investigates the effect of liquids on radial segregation of granular mixture in a rotating drum using the discrete element method. The wet granular mixture, due to differences in particle size and density, segregates in a similar way to that of dry particles: lighter/larger particles move to the periphery of the bed while heavier/smaller particles stay in the centre. An index based on the variance of local concentration of one type of particles was proposed to measure the degree of segregation. While the liquid induced capillary force slows down the segregation process, its effect on the final state is more complicated: small cohesion shows no or even positive effect on segregation while high cohesion significantly reduces particle segregation. The effect can be explained by the change of flow regimes and the competing effects of mixing and segregation (un-mixing) in particle flow which are both reduced by the interparticle cohesion. A diagram is generated to describe the combined effect of particle size and density on segregation of wet particles. A theory is adopted to predict the segregation of particles under different density/size ratios.

Research on Barite Concrete Mixed with Fly Ash

Barite concrete with density grade of 3 and strength grade of C30 was prepared by mixing with different fineness of fly ash. The workability, mechanical properties and long-term high temperature performance of the prepared barite concrete were researched. Results show that the workability of barite concrete is improved by mixing with fly ash, and no segregation of mixture has been observed. The apparent density and 3d, 28d compressive strength of barite concrete are decreased obviously after mixing with fly ash. But with the increasing of the fineness of fly ash, the apparent density and 3d, 28d compressive strength of barite concrete have a slight increase. High temperature residual compressive strength is decreased with the increasing of temperature. The cycle times of heat treatment at 400°C only has a little effect on residual compressive strength of barite concrete.

Mixing and segregation of solid mixtures in bubbling fluidized beds under conditions pertinent to the fuel reactor of a chemical looping system

Abstract Performance of chemical looping combustion processes can be improved drastically by enhancing the overall redox characteristics of the system through the use of binary mixtures of oxygen carriers. However, binary mixtures of oxygen carrier particles are often found to differ in both size and density and therefore have the tendency to segregate under certain operating conditions. In this work, a numerical study was conducted to investigate the mixing and segregation behaviour of binary mixtures of particles with different sizes and densities in a bubbling fluidized bed under conditions pertinent to the fuel reactor of a cold flow model (i.e. a non-reacting replica) of a 10 kW th chemical looping combustor. The motion of particles was tracked individually by discrete element model (DEM), whilst the gas flow was modelled by computational fluid dynamics (CFD). Gas–particle interactions were considered by a two-way coupling method. Further, a modified version of Lacey's method was developed to calculate the mixing index, taking into account both the heterogeneity of solids spatial distribution and particle size differences. Results showed that the modified Lacey's method provided very consistent and stable mixing indexes, proving to be effective for an in-situ quantitative description of mixing. It was also found that as the size ratio of the binary mixture of particles reduced, the mixing index increased indicating better mixing conditions. The agreement between the DEM/CFD model predictions and the experimental data was found to be satisfactory. The optimum conditions for mixing of binary mixtures appeared to be a function of bubble size, bubble rising rate and bubbling dynamics (e.g., splitting and coalescence). Application of the DEM/CFD model for prediction of layer inversion phenomenon in gas–solid fluidized beds was also demonstrated.

The Temperature Measuring and Evaluating Methods Based on Infrared Thermal Image for Asphalt-Pavement Construction

Abstract To investigate the temperature segregation of asphalt mixture and the corresponding influence on construction quality, the infrared thermal imager was used to detect the loading, unloading, and paving temperature of the asphalt mixture, and a pavement-quality indicator (PQI) test was used to work out the density of pavement, and several conclusions were obtained. During the mixture delivery, the inner temperature changes little, whereas the surface temperature decreases greatly. The temperature decrease during the process from the unloading to the paving is mainly caused by the heat convection of the surface mixture. The paving mixture temperature is not consistent and obviously there is variation in features serrated. The maximum temperature of mat occurs toward the end of the paving period for a truckload of mixture, the lowest temperature appears after the beginning of the paving period of the next truckload of mixture, and the process repeats in this way. Transversal temperature segregation is more obvious than the longitudinal one. Compaction degree distribution along the transverse has the same variation tendency with temperature distribution. Finally, the evaluation criteria for asphalt-pavement temperature segregation were proposed based on the percentage of the point numbers with more than 6°C variation of average temperature.

Stratification, segregation, and mixing of granular materials in quasi-two-dimensional bounded heaps

Segregation and mixing of granular mixtures during heap formation has important consequences in industry and agriculture. This research investigates three different final particle configurations of bidisperse granular mixtures--stratified, segregated and mixed--during filling of quasi-two-dimensional silos. We consider a large number and wide range of control parameters, including particle size ratio, flow rate, system size, and heap rise velocity. The boundary between stratified and unstratified states is primarily controlled by the two-dimensional flow rate, with the critical flow rate for the transition depending weakly on particle size ratio and flowing layer length. In contrast, the transition from segregated to mixed states is controlled by the rise velocity of the heap, a control parameter not previously considered. The critical rise velocity for the transition depends strongly on the particle size ratio.