Particle Mixing Process Research Articles

Experimental and Numerical Study of Computer Vision-Based Real-Time Monitoring of Polymeric Particle Mixing Process in Rotary Drum.

In the drum mixing of particulate polymers, segregation may occur. By measuring the mixing status in real time, it is possible to implement corrective measures to prevent separation and improve the efficiency of the process. This study aims to develop and validate a real-time vision system designed to monitor the mixing process of polymeric particles in a rotary drum mixer, employing a novel centroid-based model for determining the mixing index. The proposed centroid-based model is capable of addressing the radial particle segregation issue without the need for extra image-processing procedures like image subdivision or pixel randomization. This innovative approach greatly improves computational efficiency by processing over 68 image frames per second. The new processing method is 2.8 times faster than the gray-level co-occurrence matrix method and 21.6 times faster than the Lacey index approach. This significantly improves real-time monitoring capabilities and enables real-time image processing using only affordable single-board computers and webcams. The proposed vision-based system for monitoring rotary drum mixing has undergone validation via cross-validation using discrete element method simulations, ensuring its accuracy and reliability.

A mixing index for uniformly and gap-graded cohesionless particles influenced by mixing rate and diameter of stirring rods

Soil mechanics, sometimes, deals with the mixing of soil such as in deep mixing of soil and mixing of soil in tunnel boring machines, i.e., earth pressure balance (EPB-TBM) shields. The geometry of mixing apparatus such as size of stirring rods plays an important role to achieve higher degree of mixing. Moreover, the effect of gap-graded particles being mixed on degree of mixture should also be evaluated. It is important to estimate the extent of mixing of the soil to confirm the required performance of such phenomenon.This study aims to propose a simple method to quantify the degree of mixture of solid particles stirred by rotation of rods with varying diameters at different mixing rates. Discrete element method (DEM) is used to simulate the stirring process and evaluate the degree of mixture at each rotation based on the spatial distribution of different types of particles. To reduce complexity in the mixing process of particles, this study focuses on monodispersed (i.e., uniformly graded) and bidispersed (i.e., narrowly gap-graded) spherical particles where inter-particle cohesion is not considered. The DEM results reveal spatial variation of the degree of mixture (dm) in the given volume; however, its mean (dm¯) increases with the rotation number of stirring rods. Besides, dm¯ depends on the size of stirring rods whereas the mixing rate is less sensitive to dm¯ for the non-cohesive sandy particles. The dm¯ of narrowly gap-graded particles cases is slightly on the lower side as compared to that of uniformly graded particles. The results of the DEM simulations are validated through the model test.

Mixing performance of cohesive particles in a double barrel with differential velocity based on DEM

The double barrel with differential velocity (DBDV) was proposed to improve the mixture quality. However, the mixing mechanism of cohesive particles in the DBDV is unclear. So, the mixing performance of cohesive particles in the DBDV was studied. The cohesive force between particles was simulated using a viscous contact model. The effects of linear velocity, inclination and cohesive force on the mixing performance were studied. The mixing process of particles was analyzed through mixing uniformity, mixing time, velocity, and contact forces. The results show that excessive cohesion cannot promote the dispersion of particles in the mixture, affecting production efficiency. The motion intensity of particles in the differential region is stronger than that in the non-differential region. The differential zone is suitable for particle motion with high cohesion. This study reveals the detailed mixing behavior of cohesive particles in DBDV, which provides operational guidance for the actual road material mixing process.

Effect of blade configuration on the mixing process of particles in an intensive mixer

DEM simulations of particle mixing process in the intensive mixer were conducted to study the influence of blade configuration and impeller speed on the particle dynamics and mixing performance. Two tagged particles at different locations were used to discuss the influence of blade configuration on the particle trajectory and residence time in the intensive mixing region. The average magnitude velocity in the intensive mixing region, time-averaged velocity fluctuation, coordination number, impeller torque and relative standard deviation (RSD) were adopted to quantify the mixing performance during the mixing process. It was found that the blade configuration plays a vital role in the mixing process as it affects the residence time, particle velocity and mixing performance. The magnitude velocity of particles agitated by the thread blades is lower than that agitated by the arc and straight blades. The residence time for the thread blade mixer is longer than that for the arc and straight blade mixers. The mixing performance of particles in the thread blade mixer is better than that in the arc and straight blade mixers. Results obtained show that a proper impeller speed is very important for the mixing of particles, and the optimal impeller speed for granular mixing in the intensive mixer is 150 rpm.

Floating particles mixing characteristics in an eccentric stirred tank coupled with dislocated fractal impellers

Abstract The mixing characteristics of floating particle dispersion process in an eccentric stirred tank with dislocated fractal impellers were investigated using computational fluid dynamics (CFD) and experimental analyses. Solid concentration distribution, axial solid concentration profile, cloud height, solid integrated velocity, power consumption and just drawdown speed were investigated. Results showed that dislocated fractal impeller can enhance solid integrated velocity and fluid turbulent fluctuation intensity compared with dislocated pitched blade impeller, and eccentric agitation coupled with dislocated fractal impeller could destroy the typical circulation loops and symmetric flow field and improve the axial circulation efficiency of floating particles on the basis of dislocated fractal impeller. Eccentric agitation coupled with dislocated fractal impeller could further enhance the floating particle dispersion homogeneity (MI) and decrease the just drawdown speed (N jd) on the basis of dislocated fractal impeller and dislocated pitched blade impeller at the specific power consumption. Meanwhile, eccentric ratio of 0.3 or 0.4 was optimal for the floating particle mixing process in this work.

Virtual Experiments of Particle Mixing Process with the SPH-DEM Model.

Particle mixing process is critical for the design and quality control of concrete and composite production. This paper develops an algorithm to simulate the high-shear mixing process of a granular flow containing a high proportion of solid particles mixed in a liquid. DEM is employed to simulate solid particle interactions; whereas SPH is implemented to simulate the liquid particles. The two-way coupling force between SPH and DEM particles is used to evaluate the solid-liquid interaction of a multi-phase flow. Using Darcy’s Law, this paper evaluates the coupling force as a function of local mixture porosity. After the model is verified by two benchmark case studies, i.e., a solid particle moving in a liquid and fluid flowing through a porous medium, this method is applied to a high shear mixing problem of two types of solid particles mixed in a viscous liquid by a four-bladed mixer. A homogeneity metric is introduced to characterize the mixing quality of the particulate mixture. The virtual experiments with the present algorithm show that adding more liquid or increasing liquid viscosity slows down the mixing process for a high solid load mix. Although the solid particles can be mixed well eventually, the liquid distribution is not homogeneous, especially when the viscosity of liquid is low. The present SPH-DEM model is versatile and suitable for virtual experiments of particle mixing process with different blades, solid particle densities and sizes, and liquid binders, and thus can expedite the design and development of concrete materials and particulate composites.

Analyses of multi-size particle mixing behavior in an ore pre-reduction rotary kiln by discrete element method

The particle distribution in pre-reduction rotary kiln directly affects the reduction process of iron ore, and in-depth understanding of the mixing behavior is helpful to improve the product quality and productivity. The present work focused on the mixed dynamics of multi-component and multi-size systems in rotary kiln using discrete element method (DEM). We first confirmed that the final particle distribution and mixing degree are independent of the initial particle distribution, and then further discussed the influence of the key operating parameters such as rotating speed, average size ratio and filling degree on mixing behavior. The size segregation pattern of three components shows that the large particles segregated to the outer region, while the small particles were concentrated in the core region, forming an annular distribution with different particle sizes. Furthermore, the results also indicate that the rotational speed and fill degree show strong influence on the mixing time and have little influence on the mixing quality. Conversely, the average size ratio significantly affects on the mixing quality. The particle segregation is suppressed and the coal and iron ore particles are well mixed together for the whole bed when the average size of coal particles is smaller than that of iron ore particle. The findings of this work provide a reference for controlling and optimizing the particle mixing process in pre-reduction rotary kiln.

Numerical investigation of granular mixing in an intensive mixer: Effect of process and structural parameters on mixing performance and power consumption

• Mixing experiments were developed for verifying DEM model. • The mixing performance increases with the decrease of impeller offset. • The impeller with 3 blades has the highest energy efficiency. • The mixing efficiency and energy efficiency increase with the decrease of filling level. Discrete element method (DEM) simulations of particle mixing process in an intensive mixer were conducted to study the influence of structural and process parameters on the mixing performance and power consumption. The DEM model was verified by comparing the impeller torque obtained from simulation with that from experiment. Impeller and vessel torque, coordination number ( CN ) and mixing index (Relative standard deviation) were adopted to qualify the particle dynamics and mixing performance with different parameters. A method based on cubic polynomial fitting was proposed to determine the critical mixing time and critical specific input work during the mixing process. It is found that the mixing performance and energy efficiency increases with the decrease of impeller offset. The mixing performance is improved slightly with the increase of blade number and the impeller with 3 blades has the highest energy efficiency due to its low input torque. Results indicate that the energy efficiency and the mixing performance increase with the decrease of filling level when the height of granular bed is higher than that of blade.

Mixing Characteristics of Additives in Viscous Liquid BOF Slag

The mixing behavior of compositional modifiers into viscous liquid BOF slag was studied using fluid flow modeling under industrially relevant conditions. The Volume of Fluid-Large Eddy Simulation-Discrete Phase Model was used to simulate the gas-solid particle-liquid slag turbulent flow. The area fraction of the particle migration zone was calculated to quantify the mixing process. The results show that increasing gas flow rate and/or depth of lance submergence can shrink the quiescent region at the bottom of the slag pot, shortening the mixing process. Influence of the lance submergence depth is more significant on the particle mixing process. The input energy flux can be used as a measure to quantitatively evaluate the mixing behavior. Additionally, it was confirmed that increasing the slag viscosity prolongs the mixing process. Particle size in the range that was studied has little influence on the particle migration.

An improved disk discontinuous deformation analysis model for simulating particle mixing process in rotary drums

This paper develops an improved disk discontinuous deformation analysis (DDDA) model to simulate mixing particles in rotary drums. The original DDDA is improved by developing a disk-movable line segment contact model to motivate the constant movements of the disks during the mixing operation. The analytical solution of the movement of a single disk in a rotary drum is achieved by building a force analysis model, and the improved DDDA is validated by comparing this analytical solution with the proposed numerical simulation. Then, the improved DDDA is utilized to simulate mixing 8805 disks in a rotary drum, during which the influences of rotational speed and layouts of stirring blades are studies. Model performance shows that, the improved DDDA is a feasible tool to simulate the particle mixing process in rotary drums, which may optimize schemes for mixing particles and designing mixing equipment in industry.

A novel mixing index and its application in particle mixing behavior study in multiple-spouted bed

Particle mixing is a very important process in many industrial reactors. It is important to consider how to quantify the particle mixing behavior accurately under different conditions. In this paper, the drawbacks of traditional mixing indexes, such as Lacey index are discussed, and then a novel particle mixing index, without grid dependency and particle color dependency was proposed based on the neighbor distance method and coordination number concept. Its characteristics such as parameters selection, calculation method and multi-direction were discussed in details. The proposed mixing index was used for investigating particle mixing behavior in the multiple-spouted bed under conditions of different gas velocity ratios and different particle density ratios. The experimental results have been used to validate the simulation results at first. It is found that the improved mixing index is more superior and effective compared with the traditional mixing index methods, and suitable for the investigation of particle mixing behavior. It was indicated that the density ratio is a key factor to influence particle mixing process. The novel particle mixing index without grid dependency and particle color dependency is recommended to study particle mixing behavior in other particulate processes in the future.

Discrete element method simulation of the mixing process of particles with and without cohesive interparticle forces in a fluidized bed

The discrete element method (DEM) is used to simulate two types of mixing processes (radial mixing and axial mixing) of particles with and without cohesive interparticle forces in a two-dimensional (2D) fluidized bed. By using the Ashton index, the mixing degree is quantified and the differences between the mixing characteristics of particles with and without cohesive interparticle forces are compared. The cohesive interparticle forces, which impair bubble behaviors, can apparently weaken the mixing process and prolong the mixing time. This effect increases with increasing cohesive interparticle force. Radial mixing, which is mainly dependent on the convective mixing caused by bubbles, is relatively sensitive to cohesive interparticle force and shows a long mixing time, while axial mixing, which is mainly induced by the bubble wake, is less sensitive to cohesive interparticle force and presents a fast mixing process. Finally, to weaken the effect of cohesive interparticle force, an uneven air distribution is introduced, which greatly improves the mixing process by changing the bubble movement. This method may be helpful for the reduction of particle agglomeration in high-temperature fluidized beds.

Effects of particle size and region width on the mixing and dispersion of pebbles in two-region pebble bed

Granular systems and their mixing processes are widely used in various industries. The effects of size ratio and region width on the mixing and dispersion of pebbles in the two-region pebble bed are studied by discrete element method (DEM). The particle-scale mixing index (PSMI) and mixing entropy are used to quantify the particle mixing process. A similarity of mixing under different discharge rates is found after a stable two-region distribution structure is established. From qualitative observation and quantitative analysis, the mixing region is complicated in shape for the cases with greater particle size ratios. There is an increasing tendency of PSMI for two-region pebble bed when the region ratio or size ratio rises. The size ratio has greater effects on the mixing and dispersion of pebble than the region ratio, since the occupied volumes and entropies in the mixing region in the relatively steady state are more strongly affected by the size ratio rather than by the region ratio. As particles in the side regions can be easily driven by large ones, the stagnant region will decrease greatly when large size particles flow in the central region.

An image analysis technique for the particle mixing and heat transfer process in a pan coater

Pan coaters are important equipments widely used in pharmaceutical industry. The coating performance of a pan coater is greatly influenced by the particle mixing process and heat transfer process in the particle bed. However, due to lack of appropriate measuring technique, the interplay of these two processes has not been well understood yet, which brings many uncertainties in optimizing the design and operation of pan coaters. In the present work, a non-invasive optical imaging technique is introduced to monitor the dynamic process of particle mixing and heat transfer, using a D400mm pan coater filled with groups of hot particles (red colored) and cold particles (white colored) as test example. The process of particle mixing and heat transfer is recorded by a RGB camera and an infrared thermograph camera, respectively. An image processing approach is then proposed to measure the time evolution of the feature variable (particle contacts and temperature variance) of the two processes. Based on a first-order regression model, the settling time of the particle mixing and heat transfer is then calculated and compared. By introducing a dimensionless feature variable, it is now possible and convenient to compare the transient behaviors of the two different physical processes (particle mixing and heat transfer). The effectiveness of the proposed measuring technique and image analysis methods are validated by experiments.

Microfluidic mixing using unsteady electroosmotic vortices produced by a staggered array of electrodes

This paper proposes the improvement of microfluidic mixture using the unsteady electroosmotic vortices induced by a staggered array of electrodes. The unsteady electroosmotic forces near two walls, having opposite directions near two walls, were shown to drive organized vortices to contribute for the enhanced mixing. Examination was given to the flow field involving unsteady vortices and their role for the particle mixing. Numerical simulation was made to evaluate the particle mixing process and to reveal how the particle mixing occurred under influence of disturbance by unsteady vortices. The Reynolds number was set to 0.005 and 1.0 changing the oscillation frequency and the electric field intensity. Efficiency of particle mixing was evaluated by the variance intensity of particle number fraction. The agreement between the simulation for the steady electroosmotic flow and the existing paper, and the grid convergence vindicated the simulation code presently used. The numerical results for unsteady electroosmotic flow demonstrated that the particle mixing was controlled by the oscillation frequency and the balanced time scales of the flow perturbation and convection was essential to the particle mixing. The particle flow was displayed to discuss the phenomenology related to the particle mixing. This revealed that the intermingling of particles within main and secondary vortices crucial for the mixing process whereas the outside streams exerted by the vortices were not effective on it.

Numerical simulation on stirring motion and mixing characteristics of ellipsoid particles

To investigate the motion characteristics and the law of identical property for particles obtained under segregation to uniform distribution conditions in forced agitation mixing, the mixing process of the same sized ellipsoidal particles at different rotating speeds in a U-tank is simulated using three-dimensional discrete element method. Macroscopic mixing law and partial mixing characteristics in particle mixing process are analysed in the view of single particle random motion trajectory and motion vector diagram of macroscopic particle flow. And the mathematical relation between mixability and revolutions of agitating blades is described quantitatively. Results show that convective mixing and four partial mixing characteristics control the mixing homogeneity process of identical property of segregation particles in forced agitation mixing. Mixability of segregation particles is independent of rotating speed of the agitating shaft, but has a direct correlation with revolutions. The relation between mixability and revolutions agrees with the exponential growth model. Research results can provide the basis and reference for equipment improvement and operating control of bulk material in the industry of the augmenting of mix.

Comparative Study on the Characterization Method of Particle Mixing Index Using DEM Method

Different methods of particle mixing index are summarized in detail, such as average height method, nearest neighbour method, neighbour distance method, Lacey method, mixing entropy method, coordination number method, particle-scale index method and Siiria method. All these particle mixing indexes are calculated in two classical particle related process, that are the rotating drum and the spouted bed based on simulation results using DEM method. Then the comparative analysis of different kinds of particle mixing index is given in different aspects, such as calculation complexity, parameter dependency, grid dependency, color dependency and direction dependency. The performances of different particle mixing indexes are evaluated, the advantages and disadvantages of different indexes are pointed out, and the recommendation adaptation ranges are given finally. General speaking, the neighbour distance method seems as the best choice for studying the particle mixing process because of its superior performance.

Evaluation of Particle Mixing Process Using X-ray Micro-focus Computer Tomography

Evaluation of Particle Mixing Process Using X-ray Micro-focus Computer Tomography

Bioturbation, short-lived radioisotopes, and the tracer-dependence of biodiffusion coefficients

Bioturbation refers to the mixing of sediment particles resulting from benthic faunal activity. It is the dominant particle mixing process in most marine sediments and exerts an important control on diagenetic processes. In models, bioturbation is usually treated as a diffusive process where the biodiffusion coefficient (D b) characterizes the biological mixing intensity. Biodiffusion coefficients are classically computed by fitting a diffusive model to vertical profiles of particle-bound radioisotopes. One peculiar observation is tracer-dependence: D b values from short-lived tracers tend to be larger than those obtained from long-lived tracers from the same site. Recent theoretical work, based on random walk theory and Lattice Automaton Bioturbation Simulations (LABS), has suggested that this tracer-dependence is simply a model artifact and has concluded that the biodiffusion model is not applicable to the short observational time scales associated with short-lived radioisotopes. Here we have compiled a global dataset of D b values obtained from different radiotracers to assess tracer-dependence from a data perspective. Tracer-dependence is significant in low-mixing environments like slope and deep-sea sediments, but is not present in intensely mixed coastal areas. Tracer-dependence is absent when the number of mixing events is larger than 20, or the potential length scale is greater than 0.5 cm. Roughly this comes down to tracer-derived D b values greater than 2 cm 2 yr −1. This condition is met for 68%, 50%, and 8% of published D b values obtained from coastal, continental slope, and abyssal environments, respectively. These results show that short-lived radioisotopes are suitable to quantify biodiffusion mixing in sedimentary environments featuring intense bioturbation.

Gas-Phase Synthesis of Silicon Nanoparticles and Mixing with Graphite Powders by Using Counter-Flow Injection

Mixing between nano-sized silicon particles and micro-sized graphite powders was performed for anode materials of lithium ion batteries, in which the silicon nanoparticles were synthesized by silane pyrolysis under optimized conditions and were subsequently coated onto the surface of graphite powders at mixing chamber by counter-flow injection. The counter-flow injection was employed as a dry particle mixing process in order to generate uniform silicon-coated graphite powders. Furthermore, this method also made it possible to combine particle synthesis and mixing into one single operation. Energy dispersive X-ray spectroscopy (EDS) was utilized to examine the degree of mixing through surface chemical composition analysis of the mixture. Experimental results indicate that the jet Reynolds number can be considered as the key parameter to determine the homogeneity of the mixture and its critical value may be in the range of 120 to 180 for good mixing performance, being in reasonable agreement with previous studies.