Segregation Of Binary Mixtures Research Articles

Waste valorization in fluidized bed reactor: Statistical assessment of particle segregation in binary mixtures of sand and Tetra Pak residues

The fluidized bed reactor is an alternative for aluminum recovery and waste valorization of polyolefins from the polyethylene/aluminum composite (LDPE/Al). The sand is typically added as an inert particle into the fluidized bed to enhance heat and mass transfer. Such addition, however, can lead to particle segregation and compromise the reactor start-up. As a research novelty, this paper uses a 33-factorial experimental design with three central points to assess particle concentration uniformity in a fluidized bed composed of LDPE/Al and sand mixtures. A statistical procedure permits an evaluation of the factors effect of the LDPE/Al mass fraction (XC% w/w), the air velocity ratio (V/Vmf), and the diameter ratio of LDPE/Al and sand (dC/dS) on the bed mixing index (IM). Results show that only the dC/dS and V/Vmf ratio affects the IM. Data analysis reveals that fluidized beds reach axial particle uniformity with 0.67 dC/dS, 10 % V/Vmf, and 15% wt. LDPE/Al composite. The statistical model developed accurately predicts the IM, with an error of less than 15%. Such results allow applying a fluidized bed for waste-derived fuels, aluminum recovery from carton packaging wastes, and energy saving of 0.745 MWh per each ton of recovered carton package annually.

A new measurement method for mixing and segregation of binary mixture by combining gas cutting-off method and ECVT

Binary mixture fluidization is an important operation type of fluidized bed. The regularity of mixing and segregation of binary mixture is the key to process research and development. In this paper, a new experimental method for the measurement of mixing and segregation of binary mixture is proposed by combining gas cutting-off method and Electrical Capacitance Volume Tomography (ECVT). While inheriting the advantage of high applicability of gas cutting-off method, this method can be of high spatial resolution with the application of ECVT. This combination can not only obtain detailed particle component distribution information, but also reduce the experimental labor intensity. Based on the measuring principle of ECVT and Maxwell Garnett mixing model, the calibration relationship between voxel value and particle mixing ratio was deduced. An experimental binary mixture system was employed to validate the calibration relationship. The result showed that the calculated calibration curve was in good agreement with the experimental calibration curve, which indicates the rationality and feasibility of the method. On this basis, mixing process of the same particle system was quantitatively characterized and analyzed at a given air flow rate. • A new measurement method for mixing and segregation of binary mixtures was developed. • High resolution of ECVT and high application of gas-cutting method were combined. • Measuring principle was mathematically derived for isotropic binary mixture. • Mixing process of experimental binary particle system was visually studied.

Waste Valorization in Fluidized Bed Reactor: Statistical Assessment of Particle Segregation in Binary Mixtures of Sand and Tetra Pak Residues

Waste Valorization in Fluidized Bed Reactor: Statistical Assessment of Particle Segregation in Binary Mixtures of Sand and Tetra Pak Residues

Electrostatic separation of polymer waste by tribocharging system based on friction with PVC

The improper disposal and accumulation of polymer waste in the environment cause several ecological damages, and it is a challenge for our society. The mechanical recycling of polymer waste is the most appropriate alternative to decrease these problems. However, polymer recycling is not a trivial process and some difficulties, such as the segregation of different kinds of polymers in post-consume polymeric waste, represent their complexity. The segregation of post-consume polymeric waste is the main barrier for mechanical recycling of polymers. Electrostatic separation of polymeric waste based on tribocharging of polymer particles when rubbed with different surfaces has emerged as a promising method for mechanized separation of polymer waste. In present study, an apparatus for electrostatic separation of polymer waste based on tribocharging in polyvinyl chloride pipe with air flow has been development. The system has showed considerable efficiency for polyvinyl chloride segregation in binary mixtures with high-density polyethylene waste and with polyethylene terephthalate as well as in ternary mixture polyvinyl chloride/high-density polyethylene/polyethylene terephthalate.

Shear-induced particle segregation in binary mixtures: Verification of a percolation theory

Granular materials composed of different-sized grains may experience undesired segregation. Segregation is detrimental for a lot of industries because it leads to an increase in production costs and wastes. For these reasons, the segregation phenomena have been intensively studied in the last decades, and a lot of models have been provided by many researchers. However, these models are mainly based on empirical relations rather than physical considerations. This paper aims to confirm the main assumptions made by Volpato, Tirapelle, and Santomaso (2020) in their percolation theory by means of DEM simulations. The simulated geometry is a tilting shear box filled with few tracer particles in a bed of coarser sized grains, and simulations are performed for a range of tilting frequencies and size ratios. The results provide meaningful insight on the mathematical model parameters and allow us to say that the percolation theory relies on physically consistent assumptions.

Smectic–Smectic Phase Segregation Occurring in Binary Mixtures of Long and Short Rigid-Rod Helical Polysilanes

Small-angle X-ray scattering and atomic force microscopy were used to observe smectic–smectic phase segregation in binary mixtures of rigid-rod-like helical poly[n-decyl-(S)-2-methylbutylsilane] (PDMS) polymers with molecular-weight ratios of 4.82 and narrow molecular-weight distributions. Phase segregation is attributed to entropic effects as the homopolymers in the binary mixture differ only in molecular weight. Entropy-driven segregation in smectic phases was theoretically predicted in mixtures of rodlike particles with different lengths under high pressure. Binary mixtures of long and short PDMS with broader molecular-weight distributions, which do not form smectic phases, showed no such segregation, verifying that the driving force for segregation is the entropy gained through smectic-phase formation. The binary mixture of a long PDMS with a narrow molecular-weight distribution and a short PDMS with a broad molecular-weight distribution showed segregation of each component, indicating that the entrop...

Length segregation in mixtures of spherocylinders induced by imposed topological defects.

We explore length segregation in binary mixtures of spherocylinders of lengths L1 and L2 which are tangentially confined on a spherical surface of radius R. The orientation of the spherocylinders is constrained along an externally imposed direction field on the sphere which is either along the longitude or the latitude lines of the sphere. In both situations, integer orientational defects at the poles are imposed. Using computer simulations we show that these topological defects induce a complex segregation picture also depending on the length ratio factor γ = L2/L1 and the total packing fraction η of the spherocylinders. When the binary mixture is aligned along the longitude lines of the sphere, shorter rods tend to accumulate at the topological defects of the polar caps whereas longer rods occupy the central equatorial area of the spherical surface. In the reverse case of latitude ordering, a new state can emerge where longer rods are predominantly both in the cap and in the equatorial areas and shorter rods are localized in between. As a reference situation, we consider a defect-free situation in the flat plane and do not find any length segregation there at similar γ and η; hence, the segregation is purely induced by the imposed topological defects. We also develop an Onsager-like density functional theory which is capable of predicting length segregation in ordered mixtures. At low density, the results of this theory are in good agreement with the simulation data.

The effect of particle shape on predicted segregation in binary powder mixtures

Particle shape driven segregation in particulate mixtures has received limited attention in the literature either experimentally or via simulation. This study investigates the shape driven segregation which occurs during the process of heap formation and evaluates the ability of different Discrete Element Method (DEM) simulation approaches to predict the effect. It shows experimentally that the difference in particle shape can drive segregation in a binary mixture and that this segregation can be predicted by DEM models which resolve the particle shape. In this case shape is resolved via a clumped sphere approach. Importantly, the work also demonstrates that simpler models using spherical particles, with rolling friction calibrated to reproduce the experimental angle of repose, tend to underestimate the segregation tendency. The system studied was a binary mixture of irregular shaped particles, a typical spray dried detergent powder and a granulated detergent additive; particle shapes were obtained using X-ray microtomography.

A new quantitative measurement method for mixing and segregation of binary-mixture fluidized bed by capacitance probe

Dissimilar solids fluidization is a widely encountered phenomenon in many industrial processes in which the inevitable mixing or segregation phenomenon is very important for reactor design and operation. In this paper, a new quantitative measurement method for mixing and segregation of binary mixtures in bubbling fluidized bed was developed based on capacitance probe. Verification experimental results showed that capacitance probe is a reasonable method for mixing and segregation of binary mixtures. A linear relationship between probe signal and fraction distribution of solids in binary mixtures was found. Transient and steady fluidization experiments of binary mixtures with almost equal size but different densities were conducted. In transient fluidization experiments, the real-time mixing process of initially totally segregated binary solids and finally reached steady mixing state were acquired. The mechanisms of mixing processes in binary mixtures fluidized bed with different density ratios were analyzed. In steady fluidization experiments, the distribution of mixing information in bubbling fluidized bed was acquired and the results showed reasonably good agreement with theories in the literature. In summary, capacitance probe proved to be a useful method in mixing or segregation of binary mixtures fluidization.

Size Segregation of Binary Granular Mixtures - Towards more appropriate scaling of percolation velocity

We study size segregation of binary granular mixtures flowing over an inclined plane using DEM simulations. We critically examine the recently proposed scaling of the species percolation velocity with the local shear rate for different inclination angles and size ratios for an equal volume mixture of large and small spherical particles. Our DEM simulations explore a much wider range of inclination angles and shear rates for three different size ratios of large and small particles. Our results suggest that while the scaling of percolation velocity with the shear rate seems to work well for any given inclination angle, this scaling is unable to capture the influence of inclination angle on the segregation. We overcome this limitation and propose a more appropriate way of scaling the percolation velocity. This scaling, when used along with the convection-diffusion equation, is able to predict the steady state segregation of binary mixtures flowing at different inclination angles for different size ratios.

Mixing and segregation of wheat bran and vegetable pieces binary mixtures in fluidized and fluid-spout beds for atmospheric freeze-drying

ABSTRACTThe segregation of binary mixtures of nonfood wheat bran and vegetables at different levels of dryness was studied by simulating different stages of the atmospheric freeze-drying by immersion in an adsorbent material process. It was characterized using a new set of four indices, which allow to evaluate not only the segregation level but also the segregation pattern. The mixing performance was evaluated in a fluidized bed (considering also the effect of air superficial velocity) as well as in a spout-fluid bed; peas, carrot disks, and potato slabs were used as food products. In general, it was found that food material segregates toward the bed bottom during the first stages of the drying process in fluidized beds, which translates in a poor contact product-adsorbent. On the contrary, uniform mixing patterns were observed in the spout-fluid bed, for the beginning and final stages of the process. On the other hand, despite the very low cost of nonfood wheat bran and its compatibility with food materials, it presents a channeling fluidization as a consequence of the cohesive properties of its particles. This behavior was also characterized by video analysis in two different fluidized beds. A channel generation and collapse general cycle were highlighted, whose frequency and channel characteristics depend on the air superficial velocity. In addition, three main types of food particle transports were identified: passive (downward), active (upward), and particle-blocking effects. These findings allowed to explain segregation phenomena in these kinds of binary mixtures.

Three-dimensional multi-phase simulation of the mixing and segregation of binary particle mixtures in a two-jet spout fluidized bed

This study presents a three-dimensional numerical study of the mixing and segregation of binary particle mixtures in a two-jet spout fluidized bed based on an Eulerian–Eulerian three-fluid model. Initially, the particle mixtures were premixed and packed in a rectangular fluidized bed. As the calculation began, the gas stream was injected into the bed from the distributor and jet nozzles. The model was validated by comparing the simulated jet penetration depths with corresponding experimental data. The main features of the complex gas–solid flow behaviors and the mechanism of mixing and segregation of the binary mixtures were analyzed. Moreover, further simulations were carried out to evaluate the effects of operating conditions on the mixing and segregation of binary particle mixtures. The results illustrate that mixing can be enhanced by increasing the jet velocity or enlarging the difference of initial proportions of binary particle mixtures.

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.

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.

Thermal diffusion segregation in granular binary mixtures described by the Enskog equation

The diffusion induced by a thermal gradient in a granular binary mixture is analyzed here in the context of the (inelastic) Enskog equation. Although the Enskog equation neglects velocity correlations among particles that are about to collide, it retains the spatial correlations arising from volume exclusion effects and thus is expected to be applicable for moderate densities. In the steady state with gradients only along a given direction, a segregation criterion is obtained from the thermal diffusion factor Λ by measuring the amount of segregation parallel to the thermal gradient. As expected, the sign of the factor Λ provides a criterion for the transition between the Brazil-nut effect (BNE) and the reverse Brazil-nut effect (RBNE) by varying the parameters of the mixture (the masses and sizes of particles, concentration, solid volume fraction and coefficients of restitution). The form of the phase diagrams for the BNE/RBNE transition is illustrated in detail for several systems, with special emphasis on the significant role played by the inelasticity of collisions. In particular, an effect already found in dilute gases (segregation in a binary mixture of identical masses and sizes but different coefficients of restitution) is extended to dense systems. A comparison with recent computer simulation results reveals good qualitative agreement at the level of the thermal diffusion factor. The present analysis generalizes to arbitrary concentration previous theoretical results derived in the tracer limit case.

Surface segregation in binary mixtures of imidazolium-based ionic liquids

Surface composition of binary mixtures of room-temperature ionic liquids has been investigated using time-of-flight secondary ion mass spectrometry at room temperature over a wide composition range. The imidazolium cations with longer aliphatic groups tend to segregate to the surface, and a bis(trifluoromethanesulfonyl)imide anion (Tf 2N −) is enriched at the surface relative to hexafluorophosphate (PF 6 −). The surface of an equimolar mixture of Li[Tf 2N] and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF 6]) has a nominal composition of [bmim][Tf 2N] because of surface segregation and ligand exchange. The surface segregation of cations and anions is likely to result from alignment of specific ligand-exchanged molecules at the topmost surface layer to exclude more hydrophobic part of the molecules.

Nanophase segregation in binary mixtures of a bent-core and a rodlike liquid-crystal molecule

We studied mixtures of the achiral bent-core mesogen NOBOW 1,3-phenylene bis[4-(4-9-alkoxyphenyliminonetyl)benzoates] (P-9-O-PIMB) and the small, rodlike liquid crystal 8CB using high-resolution synchrotron x-ray diffraction, freeze fracture transmission electron microscopy, and differential scanning calorimetry. NOBOW and 8CB mix in an isotropic state at high temperatures but phase separate at lower temperatures when NOBOW transforms into the B4 phase and forms chiral helical nanofilaments. In pure NOBOW, the nanofilaments are close packed but at moderate 8CB concentrations, they are separated by nanosized gaps filled by 8CB. At higher concentrations of 8CB, macroscopic phase separation occurs.

Percolation segregation of binary mixtures under periodic movement

Three strain rates of 1.0, 0.5, and 0.25 Hz were selected for studying percolation segregation in binary mixtures of urea (spherical) and potash (angular). Mixed binary samples prepared from three mean coarse sizes with their corresponding three and two fines sizes for potash and urea, respectively. Herein, three coarse mean sizes 3675, 3075, and 2580 µm and three mean fine sizes 2180, 1850, and 1550 µm were selected for tests. Percolation segregation in mixed binary sample was quantified using the primary segregation shear cell (PSSC-II). Based on experimental results, the segregated fines mass, normalized segregation rate (NSR) and segregation rate of fines for binary mixtures increased with increasing strain rate from 0.25 Hz to 1.0 Hz. The NSR decreased with decreasing strain rate from 1.0 Hz > 0.5 Hz > 0.25 Hz for size ratios 1.7, 2.0, and 2.4 ( p < 0.05). At these three strain rates, for size ratio 2.0, the NSR of coarse size 3675 µm with fines size 1850 µm was smaller than the NSR of coarse size 3075 µm with fine size 1550 µm in the binary mixtures ( p < 0.05). At three strain rates of 1.0, 0.5, and 0.25 Hz, the NSR for potash was higher (53%, 56%, and 46%) than the NSR for urea for the same size ratio ( p < 0.05).

Solids Motion and Segregation of Binary Mixtures in a Rotating Drum Mixer

Mathematical modelling based on the continuum assumption and the dense phase kinetic theory is used in the work. It is found that the model captures the main features of solids motion and segregation in the drum and the results agree well with limited experimental data. The results show a clear two-region bed structure in the transverse plane of the drum operated in the rolling mode in terms of both total solids concentration and solids velocity distributions, a surface (active) layer with a low average concentration and a high velocity, and a passive layer close to the drum wall with high solids concentration and low solids velocity. The thickness of the two regions in terms of solids concentration differs greatly from that in terms of solids velocity, suggesting inaccuracy of the thin layer approximation models proposed in the past for predicting solids motion in the surface layer of rotating drums operated in the rolling mode. The results also show a clear core-shell structure in the transverse plane of the drum in terms of concentration of small and large particles. Under the conditions of this work, small particles tend to concentrate in the core region, while large particles tend to occupy the shell region, consistent with most experimental observations. Starting with a homogenous mixture of small and large particles, the above mentioned bed structures are found to be nearly fully developed within ∼2.56 drum revolutions, which is consistent with experimental observations. An initial attempt has also been made to simulate the axial particle segregation. Although the initial results are promising, more work is clearly needed to establish a better picture of axial segregation.

Segregation in binary mixtures under gravity.

We employ kinetic theory for a binary mixture to study segregation by size and/or mass in a gravitational field. Simple segregation criteria are obtained for spheres and disks that are supported by numerical simulations.