Binary Particle Systems Research Articles

Spouting behavior of binary mixtures of spherocylindrical and spherical particles in a spouted bed

Gas-solid spouted bed systems involving biomass utilization have received much attention in recent years. In actual biomass industrial processes, some fine inert particles are usually added to assist the fluidization of biomass particles. However, the flow mechanisms of binary particle systems containing biomass particles in spouted beds are still poorly understood so far. In this study, spherocylindrical particles representing biomass particles and spherical particles representing inert particles were used as the objects of study. The macroscopic and microscopic flow characteristics were explored based on CFD-DEM modeling when the volume fractions of spherocylindrical particles in the binary particle mixtures were 25 %, 50 %, 75 % and 100 %, respectively. The results showed that the minimum spouting velocities (Ums) were in the range of 150–173 m/s, but did not show a correlation with the different particle systems. During fluidization in binary particle systems, separation of spherocylindrical and spherical particles occurs. There is no significant correlation between the particle systems with different volume fractions of spherocylindrical particles and particle orientation. As the volume fraction of spherocylindrical particles increases, the average bed height of the particles decreases and the translational kinetic energy of the particles decreases/rotational kinetic energy increases. Furthermore, the wall effect influences the spherocylindrical particle orientation and volume fraction, driving the spherocylindrical particles near the wall surface toward the vertical direction.

Flow-Injection Amperometric Determination of Ceftriaxone, Cefotaxime, and Cefoperazone Using an Electrode Modified with a Binary System of Gold Particles and Mixed-Valent Ruthenium Oxides

Flow-Injection Amperometric Determination of Ceftriaxone, Cefotaxime, and Cefoperazone Using an Electrode Modified with a Binary System of Gold Particles and Mixed-Valent Ruthenium Oxides

Broken symmetries in quasi-2D charged systems via negative dielectric confinement

We report spontaneous symmetry breaking (SSB) phenomena in symmetrically charged binary particle systems under planar nanoconfinement with negative dielectric constants. The SSB is triggered solely via the dielectric confinement effect, without any external fields. The mechanism of SSB is found to be caused by the strong polarization field enhanced by nanoconfinement, giving rise to charge/field oscillations in the transverse directions. Interestingly, dielectric contrast can even determine the degree of SSB in transverse and longitudinal dimensions, forming charge-separated interfacial liquids and clusters on square lattices. Furthermore, we analytically show that the formed lattice constant is determined by the dielectric mismatch and the length scale of confinement, which is validated via molecular dynamics simulations. The novel broken symmetry mechanism may provide new insights into the study of quasi-2D systems and the design of future nanodevices.

Influence of particle stacking modes on the fluidization characteristics of biomass particles in binary particle systems

Spouted bed is widely used in biomass combustion and other industrial production due to the advantages of good heat transfer performance and sufficient gas–solid mixing. In order to achieve higher heat and mass transfer performance and conversion efficiency, inert particles are often added to assist in the fluidization of biomass particles. However, the stacking patterns of different particles in a binary particle system can have some effects on particle flow, distribution, and bed stability. Therefore, in this study, the computational fluid dynamics–discrete element method was used to analyze the particle fluidization characteristics under four different particle stacking modes in a spouted bed. The results show that the average bed height of larger spherocylindrical particles is prioritized in binary particle systems. The void fraction of spherocylindrical particles tends to increase in the near-wall region, whereas spherical particles tend to decrease. When the binary particles are mixed at the initial moment, the change rule of vertical velocity of the two particles remains consistent. In addition, the vertical velocities of two kinds of particles when layered stacking is used are gradually close to each other only after a period of time. In addition, the orientation angle of the spherocylindrical particles in the spouted bed tends to be horizontal for both the single-component spherocylindrical particle system and the wall effect attenuates this phenomenon.

Pressure fluctuations in a fluidized bed of binary particles with significant differences in particle size

Pressure fluctuation signals are investigated in a binary particle fluidized bed in which two types of particles have similar physical properties but significant differences in particle size (90 μm Vs. 1800 μm). The relationship of the measured pressure drop to gas velocity exhibits a distinct ‘‘step’’ profile, indicating that the incipient fluidization of binary particle bed can be characterized by different stages, i.e. the fixed bed, the fine particle fluidization, the coarse particle partial fluidization and the binary particle complete fluidization. And then the statistical method and scale decomposition method are used to quantify pressure fluctuation amplitude and frequency in each stage. The result shows that when binary particles are completely fluidized, the bubble size and frequency in binary particle systems are larger than that in sole fine particle systems. Additionally, binary particle systems need higher gas velocity to achieve turbulent fluidization. Furthermore, the local solids holdup measured with optical fiber probes is also employed to verify the result of pressure fluctuation analysis.

Occupation time fluctuations of an age-dependent critical binary branching particle system

Occupation time fluctuations of an age-dependent critical binary branching particle system

Pulsation effects on mixing behaviour of binary particles with different densities in supercritical water fluidized bed reactors: A CFD-DEM study

A coupled computational fluid dynamics - discrete element method (CFD-DEM) model for simulating supercritical water fluidized bed reactors (SCWFBR) is established and verified using the previous correlations based on experimental data. The CFD-DEM model is then adopted to investigate the pulsation effects on the mixing behaviour of binary particles with different densities in the SCWFBR. Numerical results show that external energy pulses can be effective in promoting the mixing of binary particle systems with different densities in SCWFBR which cannot be achieved by simply increasing the flow rate constantly. Within the current parameter range: low-frequency pulses are favored to promote particle mixing rather than high-frequency pulses, and an optimal frequency exists. The role of low amplitudes in influencing mixing degree is slight, but the particle mixing degree can be greatly enhanced by increasing the pulse amplitude beyond a certain value. The mechanism that pulsed inlet fluid promotes particle mixing is to raise the heavy particles which are inclined to stay at low positions during the fluidization. The Fast Fourier Transform (FFT) method to predict the optimal frequency established for size-induced segregation can be applicable to solve the problem of the density-induced segregation.

DEM‐CFD analysis of swelling behaviors of binary particle systems with a microscopic diffusion model

AbstractSwelling, that is, volumetric expansion, of particles is ubiquitous in many industrial systems containing both swellable particles and non‐swellable particles. However, the interactions between these two types of particles and the internal stress distribution within the binary particle systems are not yet fully understood. The dynamic behavior of binary mixtures with both swellable and non‐swellable particles was explored for the first time in this study by employing a microscopic diffusion swelling model that considers the change in microstructure of swelling particles implemented in the discrete element method coupled with computational fluid dynamics (DEM‐CFD). The expansion of particle bed consists of super absorbent polymers (SAPs) particles, that is, the swellable particles, and polyformaldehyde (POM) particles, that is, the non‐swellable particles, in a rectangle container is then analyzed experimentally and numerically. The results show that a tapered pattern of SAP particles and an arch pattern of POM particles are formed during the swelling process. The Lacey index is used to quantify the mixing degree of the binary particle system, which increases with time until the POM particle layer is fully encompassed by SAP particles. The mean stress distribution within the particle system is also examined, revealing that the swollen SAP particles migrate upward through a “low‐stress channel,” pushing the POM particles in the central area outward. Moreover, it is found that, for case with a relative low friction, SAP particles penetrate the POM particle layer along the container walls, while for the cases with relative high friction, SAP particles penetrate the POM particle layers through the central regions of the container.

Magneto-responsive hyaluronan hydrogel for hyperthermia and bioprinting: Magnetic, rheological properties and biocompatibility.

Magneto-responsive soft hydrogels are used for a number of biomedical applications, e.g., magnetic hyperthermia, drug delivery, tissue engineering, and neuromodulation. In this work, this type of hydrogel has been fabricated from hyaluronan (HA) filled with a binary system of Al2O3 nanoparticles and multicore magnetic particles (MCPs), which were obtained by clustering of superparamagnetic iron oxide FeOx NPs. It was established that the presence of diamagnetic Al2O3 has several positive effects: it enhances the hydrogel storage modulus and long-term stability in the cell cultivation medium; prevents the magnetic interaction among the MCPs. The HA hydrogel provides rapid heating of 0.3 °C per min under exposure to low amplitude radio frequency alternating magnetic field. Furthermore, the magneto-responsive hydrogel was successfully used to encapsulate cells and extrusion-based 3D printing with 87±6% cell viability, thus providing a bio-ink. The combination of high heating efficiency, softness, cytocompatibility, and 3D printability of magnetic HA hydrogel leads to a material suitable for biomedical applications.

Statistical analysis, machine learning modeling, and text analytics of aggregation attachment efficiency: Mono and binary particle systems

The aggregation attachment efficiency (α) is the fraction of particle–particle collisions resulting in aggregation. Despite significant research, α predictions have not accounted for the full complexity of systems due to constraints imposed by particle types, dispersed matter, water chemistry, quantification methods, and modeling. Experimental α values are often case–specific, and simplified systems are used to rule out complexity. To address these challenges, statistical analysis was performed on α databases to identify gaps in current knowledge, and machine learning (ML) was used to predict α under various particle types and conditions. Moreover, text analytics was employed to support knowledge from statistics and ML, as well as gain insight into the ideas communicated by current literature. Most studies investigated α in mono–particle systems, but binary or higher systems require more investigation. Furthermore, our work highlights that numerous variables, interactions, and mechanisms influence α behavior, making its investigation complex and difficult for both experiments and modeling. Consequently, future research should incorporate more particle types, shapes, coatings, and surface heterogeneities, and aim to address overlooked variables and conditions. Therefore, building a comprehensive α database can enable the development of more accurate empirical models for prediction.

Non-invasive particle-scale investigation of the effects of blade speed and particle properties on mixture homogeneity evolution using X-ray CT

A binary system of particles was mixed in a vertically bladed mixer and mixture homogeneity wasreported usingX-ray computed tomography (CT) and a particle-scale mixing index. The effects of particledensity, size, and volume fraction,as well as mixer blade speedonmixture homogeneity evolution were investigated.For same sized particles, mixture homogeneity was found todeteriorate with increasingdifference in particle densities. However, this could be countered by controlling for percolation, e.g., mixing heavier particles of larger size with smaller/lighter particles to improve mixing. Increasing blade speeds from 10 rpm to 30 rpm,deteriorated mixing,however, furtherincreases from 30 rpm to 60 rpm resulted in improvements, indicating possible flow regime changes at different rotational speeds. Increases in the volume fraction oflarge/light particles increased the penetration of these particles to the bottom layers dueto overall flowchanges,which in turnappeared to improve mixing.

Realization of the Brazil-nut effect in charged colloids without external driving

Sedimentation is a ubiquitous phenomenon across many fields of science, such as geology, astrophysics, and soft matter. Sometimes, sedimentation leads to unusual phenomena, such as the Brazil-nut effect, where heavier (granular) particles reside on top of lighter particles after shaking. We show experimentally that a Brazil-nut effect can be realized in a binary colloidal system of long-range repulsive charged particles driven purely by Brownian motion and electrostatics without the need for activity. Using theory, we argue that not only the mass-per-charge for the heavier particles needs to be smaller than the mass-per-charge for the lighter particles but also that at high overall density, the system can be trapped in a long-lived metastable state, which prevents the occurrence of the equilibrium Brazil-nut effect. Therefore, we envision that our work provides valuable insights into the physics of strongly interacting systems, such as partially glassy and crystalline structures. Finally, our theory, which quantitatively agrees with the experimental data, predicts that the shapes of sedimentation density profiles of multicomponent charged colloids are greatly altered when the particles are charge-regulating with more than one ion species involved. Hence, we hypothesize that sedimentation experiments can aid in revealing the type of ion adsorption processes that determine the particle charge and possibly the value of the corresponding equilibrium constants.

Investigation of mixing homogeneity of binary particle systems in high-shear wet granulator by DEM

To provide a theoretical foundation and a good understanding for the real manufacturing granulation process, this paper investigates the effect of particle properties on the mixing process in the high-shear wet granulator, a common equipment in one of the key technologies in the growth of the pharmaceutical industry that has rarely been used to examine particle mixing-related problems in previous numerical simulations. The discrete element method (DEM) and the relative standard deviation (RSD) to explore binary particle systems with a range of sizes, densities, and volume fractions, and measure the mixing homogeneity of the particles. Results show that, for binary particle systems, particle size, density, and volume fraction all significantly affect mixing homogeneity, with good mixing occurring for a single size and a 1:1 volume fraction for the same density. Similar Brazil nut effect and Reverse-Brazil nut effect occurrences were discovered for many particle systems at various stages. There is a size threshold for a given binary particle system. Then, in a binary system, particles of a single size and density had nearly similar vertical driving forces, and these forces may vary by up to 10 times with changes in size or density. In the end, granular temperature rises with radial position and reaches its highest point at the pelletizer’s wall and the top of the impeller. Density has less of an impact on granule velocity fluctuation than size.

Investigating the effects of material properties on the mixing dynamics of cohesive particles in a twin screw mixer using a discrete element method approach

A discrete element method (DEM) model was developed for a co-rotating twin-screw mixer (TSM) consisting of conveying and kneading elements. This model was used to simulate the mixing of a cohesive binary system of particles (P1 and P2). The particles were calibrated using angle of repose and dynamic yield strength simulations. Properties of P1 were kept constant throughout the study while properties of P2 were varied. The TSM model was used to study the influence of particle size, density, and flowability of P2 on process outputs such as powder holdup, mean residence time (MRT), and degree of mixing along the length of the TSM. All the three particle properties were varied at three-factor levels with flowability ranging from good flow (GF), poor flow (PF), and very very poor flow (VVPF) based on Carr’s classification. The model provides fundamental insights into the differences in mixing in the conveying sections of the mixer for materials with different flowability. Due to the co-rotating nature of the screws, the majority of the material in the conveying sections was carried on one side of the TSM for GF and PF particles, while both the screws carried VVPF particles. The total steady-state holdup and the mean residence time (MRT) of particles inside the TSM were heavily influenced by particle flowability compared to the other two tested particle parameters. The holdup in the conveying compartments ranged from 11%–15% of the total holdup, while the kneading compartment comprised 40% of the total holdup in the mixer. The simulations found that VVPF particles mixed the fastest and that the GF particles had the highest tendency to demix. The model was also used to suggest and test other screw design configurations to improve mixing. A screw design with kneading elements closer to the mixer outlet resulted in better mixing of GF particles. A screw design consisting only of conveying elements achieved the same degree of mixing as the original screw design for VVPF particles. • A model for a co-rotating twin-screw mixer was developed using DEM. • Holdup and mean residence time was influenced by the particle flowability. • Particles were transported mainly on one of the conveying screws. • The model was also used to suggest changes to screw design configurations.

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.

Bubble dynamics in a binary Gas-Solid fluidization system of Geldart B and Geldart D particles

In order to gain a more fundamental understanding of binary particle systems, a two-dimensional (2D) fluidized bed was used to study the bubble dynamics and dense phase composition. Digital image analysis (DIA) was employed to measure bubble diameter, bubble rise velocity, bed expansion, and the distribution of the two types of particles in the bed. Magnetite and sand particles as the single components and binary mixtures were used as the bed materials. The bubble diameter and bubble rise velocity both increased with the distance above the gas distributor and the excess gas velocity. The bubble rise velocity also increased while bubbles ascending in the bed due to an increase in bubble size and buoyancy. Both mono particle systems had higher average bubble sizes than that of the system with nearly identical particle composition, which had the smallest bubble size and the lowest bubble rise velocity. The bubble coalescence and splitting processes were also imaged and the total bubble volume was found to increase after coalescence and decrease after splitting due to some uncaptured smaller bubbles. In addition, a preliminary experiment was carried out to trace dense the phase composition and the overall bed density was estimated based on the dense phase composition and bed expansion.

Bimodal particle distributions with increased thermal conductivity for solid particles as heat transfer media and storage materials

Solid particles are being considered in several high temperature thermal energy storage systems and as heat transfer media in a variety of advanced power generation systems, particularly in concentrated solar power plants. The downside of such an approach is the low overall heat transfer coefficients caused by the inherently low thermal conductivity values of the low-cost solid media when coupled to heat exchanger for the power cycle working fluid. Choosing the right particle size distribution, emittance, and material of the solid media can all make a substantial difference in packed bed thermal conductivity. Current research though exclusively focuses on continuous unimodal distributions of particles. Here, we propose the use of a binary particle system with a bimodal size distribution to significantly increase packed bed thermal conductivity by reducing packed bed porosity. This is the first study related to ceramic solid particle heat transfer that has considered the thermal conductivity of non-unimodal size distributions at room and elevated temperatures. The following study found that for the binary particle system using Carbo particles CP 16/30 – CP 70/140 where the large particle volume fraction was 50% there was an 17–47% increase in packed bed thermal conductivity when compared with a nearly unimodal particle size distribution of CP 16/30 between 50 and 300 °C. Two different porosity and effective thermal conductivity models were studied, with one providing better prediction of porosity but both effective thermal conductivity models providing less predictive capacity. Importantly this approach can have a substantial impact of thermal performance, with little to no impact on the particle cost.

Comparison of hydrodynamics in a gas-solids fluidized bed with binary particle systems for dry coal beneficiation

Fluidization behaviour of two binary particle systems, magnetite225-sand225 (M225-S225) particles with the same mean diameter (dp) and magnetite225-sand304 (M225-S304) particles with the same aerodynamic diameter (da) were observed in a two-dimensional fluidized bed. The number, size and rise velocity of gas bubbles in the binary fluidized bed were characterized by image analysis. A decreasing minimum fluidization velocity (Umf) with increasing sand volume fraction was found in the M225-S225 system while a nearly constant Umf was found in the M225-S304 system. Increasing trends of both bubble size and bubble rise velocity along the bed height were detected and a linear correlation between the bubble size and rise velocity was found for binary systems. The higher the fraction for one type of particles in the binary system is, the closer to the corresponding single-component system the hydrodynamic phenomena and bubble properties will be in both binary systems.

Computation of Hydrodynamic and Capillary Phenomena in Binder Jet Three-Dimensional Printing

Abstract The fundamental operation in binder jet three-dimensional printing is the deposition of liquid binder into a powder layer to selectively bond particles together. Upon droplet impact, the binder spreads into the powder bed forming a bound network of wetted particles called a primitive. A computational fluid dynamics framework is proposed to directly simulate the capillary and hydrodynamic effects of the interfacial flow that is responsible for primitive formation. The computational model uses the volume-of-fluid method for capturing dynamic binder-air interfaces, and the immersed boundary method is adopted to include particle geometries on numerical Cartesian grids. Three-phase contact angles are prescribed through an interface extension algorithm. Binder droplet impact on powder beds of varying contact angle are simulated. Furthermore, the numerical model is used to simulate liquid bridges connecting binary and ternary particle systems, and the resulting capillary and hydrodynamic forces are validated by comparison with published experimental and theoretical model results.

Apparent viscosity of binary particle system in gas-solid separation fluidized bed

The apparent viscosity of binary particles has a crucial impact on the efficiency of gas-solid separation fluidized bed. Herein, apparent viscosity of the binary particles consisting of magnetite and coal particles was measured by the falling ball method. The test results indicate that the apparent viscosity of binary particles decreased with the increase in coal powder. When the mass fraction of coal increased by 2%, the apparent viscosity, on an average, decreased by 0.12 Pa·s, and dropped by half with increase in operating gas speed from 9.5 cm/s to 12.2 cm/s. The adjustment of gas velocity and magnetite powder content can effectively reduce the apparent viscosity and improve the separation efficiency, without changing the bed density. A modified model has been developed for predicting the apparent viscosity of binary particle. The model performed well in estimating the viscosity with an overall standard deviation of 13.00% from experimental results.