Binary Granular System Research Articles

Investigating binary granular mixing in a rotating drum using ultrafast X-ray computed tomography

The transient mixing dynamics of an initially segregated binary granular system in a half-filled rotating drum are experimentally investigated. The granular system consists of spherical beads having identical size. The density ratio between the two granular phases is 2.8. With its ability to scan three-dimensional opaque systems with a high frequency, the ultrafast X-ray computed tomography is used to capture the transient and steady-state segregation dynamics in the bulk. The segregation dynamics are also compared to those at the circular end-wall caps, which have been captured with a camera. The results show an axial migration of the denser particles towards the bulk and, more importantly, second-order overshooting dynamics in the radial mixing index, which tend to increase with the Froude number. The results will find application in industrial systems, where rapid mixing occurs. We also believe the presented data can serve as validation for future three-dimensional simulations focusing on the transient formation of segregation patterns in the bulk.

Electroconductometer via Arduino for measurement in aqueous suspensions

Real-time electroconductivity monitoring is important in several industry instances. However, this monitoring in aqueous solutions or suspensions (e.g. mineral slurries), applying direct current, is problematic due to electrode polarization, which is the accumulation of ions at the electrode-solution interface. In this study, a low-cost circuit developed is based on Arduino, allowing real-time measurement. It has annular electrodes and operates at a frequency of 1.0 kHz, simulating an alternating current signal, in order to diminish the deleterious effect of interfacial polarization and electrolysis on the electrodes. Through calibration using standard KCl solutions, a measurement range of 0.002 S/m to 1,000 S/m was obtained with good accuracy and precision. Its use is exemplified here by predicting the porosity of suspended binary granular systems.

DEM modelling and analysis of the mixing characteristics of sphere-cylinder granular mixture in a rotating drum

Mixing structures and characteristics are crucial to the mixing quality of spherical/cylindrical binary granular systems like the biomass-coal mixtures which can affect energy release and carbon emissions. In this work, the mixing of binary spheres/cylinders in a rotating drum was numerically reproduced by using discrete element method (DEM). Systematic parametric studies were conducted to identify the role of various parameters such as rotation speed (ω) of the drum, aspect ratio (AR), mass fraction (φc) and volume fraction (φv) of cylindrical particles, and the density difference (φρ) between the binary particles; meanwhile, corresponding mechanisms were also explored by analyzing the kinetic energy. Results show that when the flow regime is rolling/cascading, the mixing quality can be effectively improved; however, when the flow regime is cataracting, the mixing quality becomes worse. With AR close to 1.0, the interlocking effect between particles becomes weaker and the porosity becomes smaller, which leads to the higher contact efficiency and thus improves the mixing quality. Binary mixtures with different φc are synergistically affected by energy input and interlocking structure. The volume of spherical particles is more conducive to improving the mixing quality than that of cylindrical particles when the volume of the granular system is at the same level. The φρ can cause segregation behavior of particles so as to make the mixing quality worse.

Numerical study of forced axial segregation of binary density granular system in a split rotary drum

• Segregation of binary density particles in a split drum was studied. • The effects of sub-drum speed on segregation were analyzed. • The effects of split position on segregation dynamics were investigated. Driving and controlling the segregation in a rotary drum is both a theoretical and a practical challenge in powder technology. A novel horizontal split drum design composed of two reverse rotating sub-drums was explored to drive axial segregation of granular matter. DEM (Discrete Element Method) simulations were performed to study the particle dynamics and segregation performance of binary density particles in the split drum. Then, the effects of drum speed, the speed ratio of the two sub-drums, and the split position on the axial segregation were analyzed. It was found that true axial segregation occurred in the split drum and heavier particles tend to accumulate in the region near the split. An increase in drum speed can accelerate the segregation but it has no obvious influence on the final axial distribution of particles. The results obtained indicate when two sub-drums rotate at different speeds, the concentrated region of heavier particles moves towards the low-speed sub-drum. These findings could lead to new designs for a broad range of particle processing industries.

Prediction of segregation characterization based on granular velocity and concentration in rotating drum

In a binary granular system composed of two types of particles with different granule sizes and the same density, particle sorting occurs easily during the flow process. The segregation pattern structure is mainly affected by the granular velocity and granular concentration in the flow layer. This paper reports on the experimental velocity and concentration measurement results for spherical particles in a quasi-two-dimensional rotating drum. The relationship between the granular velocity along the depth direction of the flow layer and granular concentration was established to characterize structures with different degrees of segregation. The corresponding relationships between the granular velocity and concentration and the segregation pattern were further analyzed to improve the theoretical models of segregation (convection–diffusion model and continuous flow model) and provide a reference for granular segregation control in the production process.

Impact of Rolled and Crushed Aggregate with Natural Pozzolan on the Behavior of HPC

High performance concrete (HPC) has several advantages in building construction that cannot be achieved using conventional concrete in terms of strength durability, resistance to chemical attack, and workability of high performance concrete are high. The introduction of fillers and additives contributed to the improvement of high-performance concrete (HPC), other parameters also influence the performance of these HPCs, coarse aggregate fraction is known to strongly influence both fresh and hardened concrete’s properties. Consequently, selection of both content and particle size distribution for (HPC) mixture is an important issue regarding the predicted performance of concrete. For to make concrete more improvement , the porosity of the granular skeleton as well as the rheology of our HPC, 3/8 fraction of rolled gravel with smooth and rounded surfaces was introduced, in substitution for the crushed gravel of the same fraction , by testing various combinations of fractions 3/8 of rolled gravel and fraction 8/15 of crushed gravel in the present study, and based on previous results obtained the combinations 35,40 and 45% fraction 3/8 of rolled gravel and 65 , 60 and 55% fraction 8/15 of crushed gravel (binary granular system) respectively, gives a minimal porosity . Super plasticizer and four percentages of pozzolan were experimented. Compressive strength function of coarse aggregate was determined at 7, 14 and 28 days. Results have revealed that the mixtures with modified granule size distribution system ,1.5% of superplasticizer and 5% by weight of pozzolan allow an improvement in the compressive strength of 35.1% relative to the control concrete.

Fluid flow assisted mixing of binary granular beds using CFD-DEM

In process industries, the study of granular mixing can substantially optimize energy costs and the quality of final products. In this work, we study the mixing of binary granular systems assisted by fluid flow through the assembly. The granular system is exposed to continuous fluid flow from the bottom to the top. Particle mixing is simulated by the coupling of Computational Fluid Dynamics (CFD) and the Discrete Element Method (DEM). Parameters like particle stacking order, density ratio, and size ratio show a significant influence on mixing. The presence of tilted plates as a geometric intervention with different configurations plays a critical role in mixing efficiency. A new mixing index which captures the nature of contact creation, and the degree of mixing is proposed. The present work helps develop efficient strategies for particle mixing in fluidized beds.

Micro-mechanical (granular) mixtures for environmental safety technologies

One of the most significant problems that belong to effective use of granular materials GM (for example, in the construction, pharmacological, chemical, agricultural and some other industries, as well as in the technologies of screening against internal radiation) is the difficulty of ensuring their maximum compaction in order to increase the efficiency of their practical application. In this way, we study of the properties of binary granular systems, the dynamics of their compaction and the impact on this process of the ratio of component sizes and partial parameters in order to provide an innovative step in the development of appropriate technologies. To this end, we propose to use the apparatus of Kirkwood-Buff theory in combination with model equations of state, like Carnahan-Starling, together with relevant phenomenological information, which obtained from direct observations. We report theoretically the fundamental possibility of increasing the degree and speed of packaging and at first describe substantiate empirical data in the full range of values of the volume (or molar) fraction.

Vertical separation criterion of binary particles under external excitation

Vertical separation occurs in the binary granular system and varies with most factors of external excitation and particle properties, that is complex to explain and predict. We propose that it can be discussed from two aspects: 1) the influence of the specific external-excitation condition and 2) the separation response of the system itself. Based on the percolation and filling behaviors of particles, a vertical separation criterion is presented to discuss the above two aspects with vibration frequency f, dimensionless vibration acceleration Г, airflow velocity u, particle size ratio φd, density ratio φρ and total mass ratio φM when the container size and the granular system's packing height are fixed. In our criterion, Brazil nut separation (BN, large particles rise to the top), reverse Brazil nut separation (RBN, large particles sink to the bottom), and their crossover line (It can present as a MIX distribution where particles mix uniformly) are discussed. It's found that the system with strong separation response (a low φM/φd3φρ) tends to show a strong BN or RBN separation under appropriate conditions of vibration and/or airflow. Conversely, the system with weak separation response (a high φM/φd3φρ) inclines to separate weakly or mix uniformly.

End-wall effects on the mixing process of granular assemblies in a short rotating drum

The mixing process of binary granular systems in a short rotating drum was investigated by performing discrete element simulations. The drum was asymmetrically operated with the left end wall being fixed and the right one rotated with the side wall. The modeled granular materials were made of particles with same size and density but different colors (red and yellow). These yellow and red particles were initially arranged side by side axially. We observed that the system inevitably went through a transient radial segregation state before reaching the final homogeneous mixing state. Depending on the filling degree and rotating speed, there existed totally three types of radial segregation pattern: yellow particles were enveloped radially by red particles (R-Y pattern), red particles were besieged radially by yellow particles (Y-R pattern), and the sandwich type R-Y-R pattern. Analyses of the axial flow field show that such transient radial segregating phenomena were induced by different axial transporting characteristics of particles. The average axial motion of particles in the flowing layer and the location of the boundary between flowing layer and fixed bed layer influenced the transient radial configuration.

CFD-DEM investigation of the fluidization of binary mixtures containing rod-like particles and spherical particles in a fluidized bed

In the energy conversion process, the inert bed material such as sand with spherical shape is usually added to the fluidized bed for the proper fluidization of the non-spherical biomass particles. Understanding fluidization of the binary mixtures containing the biomass and the bed material is therefore significant for better utilization of the biomass. To this end, CFD-DEM model is used to simulate the fluidization of the binary mixtures containing the rod-like particles that represent the light and large biomass particles and the spherical particles that represent the dense and small bed material, in which all particles are described by super-ellipsoid model. Five granular systems with different volume fractions of the rod-like particles but the same particle volume are simulated in this paper. The simulation results demonstrate that the minimum fluidization velocity would increase with the volume fraction of the rod-like particles. The addition of the spherical particles is beneficial to the fluidization of the rod-like particles. The mixing rate in binary granular system and the distribution of the coordinate number would be affected by the gas superficial velocity and the volume fraction of the rod-like particles. For the orientation of the rod-like particles, its distribution in binary granular system is different from that in monodisperse rod-like particle system. But whether in binary granular system or monodisperse rod-like particle system, there is apparent wall effect on the particle orientation.

Energy-dissipation correlated size separation of granular matter under coupling vibration and airflow

Air was blown into a vertically vibrating three-dimensional bed from its perforated bottom to control the size separation of a binary granular system in experiment. We focused on the effects of dimensionless vibration acceleration Γ and air velocity u on the separating state. A model was investigated, in which energy dissipation was calculated and linked to the driving force exerted on particles. The acceleration difference of binary particles was calculated by the main parameters of vibration, airflow, and physics properties of particles. The particle motion and redistribution have been explained and predicted with the fundamental theory of dynamics. We noticed that Brazil nut (BN) separation was caused by vibration, and turned to its reverse, but with the stronger energy dissipation when Γ was increased. Reverse Brazil nut (RBN) separation was observed with a rising u, meanwhile the dissipated energy was declined. However, an improved Γ weakened the airflow-induced RBN separation. Various transitional forms between BN and RBN separations, such as uniformly mixed distribution, were obtained. In conclusion, the energy-dissipation correlated size separation can be controlled and predicted under coupling vibration and airflow.

Enhancing the linear flow of fine granules through the addition of elongated particles.

Sandglasses have been used to record time for thousands of years because of their constant flow rates; however, they now are drawing attention for their substantial scientific importance and extensive industrial applications. The presence of elongated particles in a binary granular system is believed to result in undesired flow because their shape implies a larger resistance to flow. However, our experiments demonstrate that the addition of elongated particles can substantially reduce the flow fluctuation of fine granules and produce a stable linear flow similar to that in an hourglass. On the basis of experimental data and previous reports of flow dynamics, we observed that the linear flow is driven by the “needle particle effect,” including flow orientation, reduced agglomeration, and local perturbation. This phenomenon is observed in several binary granular systems, including fine granules and secondary elongated particles, which demonstrates that our simple method can be widely applied to the accurate measurement of granular flows in industry.

Effect of granular shape on angle of internal friction of binary granular system

The study of angle of internal friction (ΦI) is widely prevalent due to its importance in science and engineering, and yet the quantitative description concerning the effect of granular shape on the ΦI is few. In our study, the influence of granular shape on the ΦI of various binary granular systems was investigated theoretically and experimentally with a Freeman FT4 Powder Rheometer. The results show that the variation amplitude of tangent ΦI (ΔtanΦI) exhibits a linear relation with the related particle physical properties. Our findings show that three regions have been divided for various binary granular systems based on their magnitude of aspect ratio, and there exists a powder function between ΔtanФI and granular shape factors. On this basis, an integrated model has been proposed to describe the quantitative relationship between angle of internal friction and granular shape factor, which agrees well with the experimental data.

Density-Driven Segregation in Binary and Ternary Granular Systems

We present a first experimental study of density-induced segregation within a three-dimensional, vibrofluidised, ternary granular system. Using Positron Emission Particle Tracking (PEPT), we study the steady-state particle distributions achieved by binary and ternary granular beds under a variety of differing system parameters. In doing so, we determine the extent to which the segregative processes in ternary systems resemble their comparatively well-researched binary counterparts. We examine the influence of particle elasticity on the system, demonstrating the existence of a significant parameter range for which the effects of inelasticity-induced segregation may be safely neglected. Finally, we investigate the existence of a causal link between convective motion within a system and the segregative behaviours observed.

Center of mass scaling in three-dimensional binary granular systems.

Using a combination of experimental results acquired through positron emission particle tracking and simulational results obtained via the discrete particle method, we determine a scaling relationship for the center of mass height of a vibrofluidized three-dimensional, bidisperse granular system. We find the scaling to be dependent on the characteristic velocity with which the system is driven, the depth of the granular bed, and the elasticities of the particles involved, as well as the degree of segregation exhibited by the system and the ratio of masses between particle species. The scaling is observed to be robust over a significant range of system parameters.

Effect of storage time on the flowability of biomass-coal granular system

The influence of storage time on the flowability of biomass-coal blends is experimental and theoretical investigated. The results show that there exists exponential relationship between discharge rate and storage time in an appropriate rice straw mass fraction range (less than 10%). In addition, the mechanism of gravity discharge rate variation for biomass-coal blends is theoretically investigated by analyzing the porosity variation of particle bed. The mechanism of porosity variation in the binary granular system is theoretically analyzed on the basis of emergent gas, mutual compression and particle rearrangement, and a mathematical model has been developed which agrees well with the experimental results. Furthermore, relaxation effect is proposed, which is mainly induced by elasticity of rice straw particle and cohesion of blends. Relaxation time is the most important parameters determining this effect. The latter decreases with increasing of coal particle size and biomass mass fraction.

Self-diffusion, local clustering and global segregation in binary granular systems: The role of system geometry

Using positron emission particle tracking (PEPT), the influence of system geometry on the dynamical and segregative properties of a three dimensional, vibrofluidised granular system is explored. A relationship between the aspect ratio of a system and the degree of segregation observed is established, demonstrating the ability to adjust segregation intensity within a system simply by modifying its aspect ratio without altering any other parameters, including the number of particles within the system, its volume and the manner in which it is driven. Such a relationship is potentially of value in future research, as well as in industrial settings. The range over which this relationship is valid is determined in terms of the quantity q, the ratio of heating to cooling events within an excited granular system. Within this range, a relationship between self-diffusion, D, and aspect ratio, A, of the form D=αexpβAγ is also proposed. Finally, this study presents what is believed to be the first experimental evidence of sudden chain energy transfer events, a phenomenon recently discovered in two-dimensional granular beds, in a three-dimensional system.

Influence of thermal convection on density segregation in a vibrated binary granular system.

Using a combination of experimental results and discrete particle method simulations, the role of buoyancy-driven convection in the segregative behavior of a three-dimensional, binary granular system is investigated. A relationship between convective motion and segregation intensity is presented, and a qualitative explanation for this behavior is proposed. This study also provides an insight into the role of diffusive behavior in the segregation of a granular bed in the convective regime. The results of this work strongly imply the possibility that, for an adequately fluidized granular bed, the degree of segregation may be indirectly controlled through the adjustment of the system's driving parameters, or the dissipative properties of the system's side-boundaries.

Separation patterns between Brazilian nut and reversed Brazilian nut of a binary granular system

This paper studies the segregation behavior of binary granular particles with diameters at approximately 10:1 in a vertically vibrated container. An array of transitional separation patterns between reversed Brazilian nut (RBN) and Brazilian nut (BN) separations are observed, with their geometrical features carefully measured. The binary particle system develops into either a stable separation pattern when f and Γ are relatively low or an oscillating pattern when f and Γ are relatively high. We regard these patterns as different phases, in which the stable patterns can be divided into phases of RBN, RBN transitional (RBNT), BNT, and BN. A phase parameter λ between-1 and 1 is defined to describe the separation patterns based on the mass center height difference in large and small particles. By drawing f-Γ-λ phase diagrams, the system's tendency toward BN separation was found to increase with f and decrease with Γ. Furthermore, the range of the tendency toward BN separation expands when the size of small particles rises. As the total mass of the small particles increases, the system's tendency toward RBN separation is enhanced. Abnormal points are also observed in the stable phase regions, and the oscillating phase shifts among the four stable phases with time. These stable phases can be explained via an analysis of the distribution of the dissipation energy, whereas the mechanism of the oscillating phase remains to be discovered.