Spiral Jet Mill Research Articles

4-way coupling CFD-DEM simulation of particle breakage and classification in a spiral jet mill: A critical analysis

Jet-milling is a particle engineering process widely adopted in industrial manufacturing to reduce the particle size of powders. Computational Fluid Dynamics simulations (CFD) coupled with Discrete Element Modelling (DEM) proved to be a valuable tool to tackle the complexity and the non-linearity of particle breakage and classification occurring in mills. To date however, they have been employed to address only single aspects of process design being unable to reproduce it completely. The coupled CFD-DEM simulations presented in this work are for the first time capable of simultaneously describe particle fragmentation, particle-gas interaction and classification. Through coarse-graining, realistic amounts of powder can be simulated allowing to demonstrate/study how the hold-up mass slows down the milling gas affecting classification and thus the milling performance. Bottlenecks/limitations of model and methodology are critically examined to understand what is currently preventing us from creating a digital twin of the milling process.

Effects of Diffusional Particle Motion on Size Classification in a Spiral Jet Mill

Effects of Diffusional Particle Motion on Size Classification in a Spiral Jet Mill

Optimization of the Classifying Efficiency of Spiral Jet Mills by Investigating the Flow Conditions and the Grinding Performance

AbstractThe achievable grinding fineness of spiral jet mills does not only depend on the comminution efficiency in the region of the nozzle jets but is also significantly affected by the separation efficiency in the region of the product outlet. Therefore, the aim of this study is to investigate the influences of the product outlet diameter and different particle trap rings on the flow conditions and the grinding performance, optimizing the classifying efficiency of spiral jet mills. The velocity fields analyzed by particle image velocimetry and the experimental grinding results show that the classification process can be optimized by both reducing the product outlet diameter and installing a particle trap ring.

Analysis of the particle collision behavior in spiral jet milling

Collision behaviors of particles in spiral jet milling were analyzed by using a simulation. The motion of the particles was tracked by the discrete element method (DEM), and the air flow was represented by the computational fluid dynamics (CFD). The DEM was coupled with the CFD by a one-way coupling method. The simulated air flow was validated by comparing the fluid velocity field with the measured one in a model experiment. Furthermore, the air flow and particle behaviors in a spiral jet mill used commercially were analyzed by using the simulation. As a result, the particles with a region balancing between centrifugal and radial drag forces could be mainly ground by the high-speed collisions between the particles circulating near the top and bottom walls of the grinding chamber.

Experimental Investigation of the Flow Conditions in Spiral Jet Mills via Particle Image Velocimetry—Influence of Product Outlet Diameter and Gas Flow Rate

Spiral jet mills used for fine and colloid grinding have an enormously high energy consumption resulting in a great potential for optimization. In order to increase their efficiency, it is essential to precisely understand the flow conditions within the grinding chamber and the influencing parameters. In this work, the experimental method of particle image velocimetry is applied, which is optimized to the extent that the velocity fields of the grinding gas flow can be determined in the entire mill cross-section. Additionally, the influence of the product outlet diameter and the grinding gas flow rate on the flow profiles are investigated. With decreasing outlet diameter, significantly higher velocities are obtained in the inner mill region resulting in higher classifying efficiencies. At the same time, as the outlet diameter declines, an overpressure builds up in the mill, causing a deceleration of the entire flow in the outer region, preventing the complete formation of the nozzle jets and leading to worse comminution efficiencies. Therefore, there is an optimum between the competing comminution and classifying processes regarding the effect of the product outlet diameter. In contrast, increasing the gas flow rate can consistently achieve a gain in velocity, improving both comminution and classifying efficiency.

Manufacturing of urea co-crystals by spiral gas–solid two-phase flow (S-GSF) based on spiral jet mills: a continuous, solvent-free, and scalable mechanochemical method

A S-GSF method based on spiral jet mills for the continuous, solvent-free, and scalable mechanochemical preparation of four urea co-crystals for the first time.

Surficial Sulfur Loss of Jet-Milled Li6PS5Cl Powder under Mild-Temperature Heat Treatment

All-solid-state batteries employing inorganic solid electrolytes are considered a promising next-generation energy storage system. Especially, argyrodite-type Li6PS5Cl (LPSCl) was highlighted for its good ionic conductivity and malleability. In the electrode level, achieving an efficient Li+ pathway even with the maximized active material proportion and electrode mass loading is vital for a high energy density. Therefore, a smaller solid electrolyte particle is highly sought for. Herein, we demonstrated a spiral jet mill process for refining LPSCl particle size. The mean particle size (D50) of LPSCl was reduced from 39.9 to 1.9 μm where the ionic conductivity was decreased from 2.0 to 0.23 mS cm–1. The post-annealing in a mild-temperature range (T < 250 °C) led to the even more decreased ionic conductivity. Although the ionic conductivity was restored when T > 300 °C, this high-temperature annealing resulted in severe particle agglomeration. Spectroscopic observations revealed that particle surfaces were damaged during pulverization and irreversible sulfur losses occurred during the mild-temperature annealing.

Application of coarse-graining for large scale simulation of fluid and particle motion in spiral jet mill by CFD-DEM

Spiral jet milling is commonly used for size reduction of high value particulate solids, such as pharmaceutical ingredients, for which low contamination is critical. The mill utilises high-pressure gas nozzles to form an internal vortex and induce particle breakage through inter-particle collisions. Due to the centrifugal flow field, the particles can move radially inwards towards the mill centre and escape the mill only when their size is sufficiently reduced for the fluid drag to exceed the centrifugal force. Large particles move radially towards the outer wall and form a dense particle bed. The bed itself circulates in the milling chamber due to the induced effect of the inclined gas jets. In this study, we analyse the implementation of a coarse-graining (CG) approach on a coupled Computational Fluid Dynamic-Discrete Element Method simulation. Along with the actual particle size, four CG scale cases are compared (CG-2, CG-4, CG-8 and CG-10). To analyse the success of the approach in predicting the dynamics of fluid and particle motion, the characteristic features of the particle bed and fluid field, i.e. the fluid and particle velocity distributions and dissipated energy through particle collisions are analysed. There is good agreement between the original particle size and the two smallest scaled cases (CG-2, CG-4) for the above characteristics. However, modelling the lean phase is less successful, as there are fewer particles that reside there at any given time. There is also good agreement between these three cases in terms of dissipated energy through particle collisions. An average value for dissipated energy of 0.6 mJ is recorded for each of the three lowest cases. This proves beneficial for simulation time required, as the particle number is reduced 2-fold and 4-fold, respectively, and interparticle collision rate is reduced 60% each time. Application of the Coarse Grain method in a spiral jet mill using coupled Computational Fluid Dynamics and Discrete Element Method Modelling. Top: Original particle size system and four scaled systems. Bottom: Resulting temporal average dissipated energy through interparticle collisions and particle wall collisions. • Coarse graining method is applied in the spiral jet mill using a CFD-DEM framework. • Particle and fluid motion is similar in the bed at smaller scales. • Insufficient particles were present in the lean phase to model the original system. • Temporal dissipated energy remained constant for low coarse grain numbers.

Influence of particle trap rings with different shapes and heights on the performance of spiral jet mills

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Comminution efficiency of spiral jet mills with different grinding nozzle types and shapes

Comminution efficiency of spiral jet mills with different grinding nozzle types and shapes

A novel uncoupled quasi-3D Euler-Euler model to study the spiral jet mill micronization of pharmaceutical substances at process scale: model development and validation

In this work we present a novel approach to model the micronization of pharmaceutical ingredients at process scales and times. 3D single-phase fluid-dynamics simulations are used to compute the gas velocity field within a spiral jet mill which are provided as input in a 1D compartmentalized model to calculate solid velocities along the radial direction. The particles size reduction is taken into account through a breakage kernel that is function of gas energy and local solid hold-up. Simulation results are validated against micronization experiments for lactose and paracetamol, comparing the model predictions with D10, D50 and D90 diameters values coming from Design of Experiments isosurfaces.The developed model allows for a fair estimation of the outlet particle size distribution in a short computational time, with very good predictions especially for D90 values.

Analysis of grinding in a spiral jet mill. Part 2: Semi-batch grinding

The breakage and classification of particles in a spiral air jet mill, operated in a semi-batch mode, is studied for varying operating conditions. The particle size distributions of the product leaving the mill and the material inside the mill are measured, along with the mass in the mill. The median particle size of the product is found to be unchanged with inlet jet pressure at about 5 μm but increases with holdup to about 7.5 μm. At low pressures and high holdups, the classification is imperfect and a significant fraction of large particles, in the size range 150–350 μm, exit in the product. The mass flux from the mill increases with both pressure and holdup and an empirical expression is given to calculate it. A population balance model is presented, which predicts size distributions, mean sizes and mass flux from the mill, in agreement with the measurements.

Influence of nozzle angle and classifier height on the performance of a spiral air jet mill

We study the effect of varying air jet mill design parameters, the nozzle angle and the classifier tube height, on the performance of the mill, operated in the semi-batch mode, using quartz and limestone particles as feed. Particle size distributions of the product and the material in the mill are measured along with the mass in the mill. The product size distribution and the specific mass flux are found to be constant with time. The breakage rate is found to increase with nozzle angle. The efficiency of classification, characterized by the fraction of coarse particles larger than the cut size, increases with nozzle angle and classifier tube height. The energy for grinding per unit mass of the product decreases with nozzle angle and increases with classifier tube height and optimal values of the parameters, at which the specific energy is minimized, are obtained.

Effect of grinding nozzles pressure on particle and fluid flow patterns in a spiral jet mill

Spiral jet mills utilise high-pressure gas jets, which induce particle breakage by collisions. Appropriately angled jets force particles to circulate in dense phase near the wall due to the centrifugal field. Moving radially inwards towards the mill centre, the two-phase dense flow is transformed into a lean phase and fine particles are entrained out by the fluid drag. Here we analyse the effect of grinding nozzles pressure on the particle dynamics and fluid flow by numerical simulation. The average velocity gradient in the radial direction is very steep for low mass loadings, indicative of rapid shearing, but it decreases significantly as the particle mass loading is increased. The dissipated collisional energy, accountable for size reduction, is strongly influenced by the jet penetration through the circulating bed, which in turn depends on the mass loading and operating pressure of grinding gas nozzles. As a result of jet penetration, the grinding gas nozzles pressure becomes less effective at high pressures. The analysis developed here elucidates the coupled effect of mass loading and grinding nozzles pressure on the dissipated collisional energy, which accounts for particle breakage.

A detailed CFD analysis of flow patterns and single-phase velocity variations in spiral jet mills affected by caking phenomena

In this work we present a method to investigate the fluid-dynamics of a 3D, real-scale spiral jet mill when caking is occurring. CFD simulations are employed to deeply study the pressure and the velocity fields of the gas phase when the nozzles inlet pressure and the chamber diameter are varied to mimic the condition generated by the aggregates formation during the micronizaton process. The computational model is built replicating the experimental observation consisting in the fact that most of the crusts form on the outer wall of the chamber. Simulations underline that caking causes the deterioration of the classification capabilities of the system if the gas mass flow rate is kept constant at nozzles, allowing larger particles for escaping the system. It is shown that it is possible to mitigate this phenomenon by gradually reducing the gas mass-flow rate to keep constant the nozzles absolute pressure. This keeps unchanged the fluid spin ratio and the classification characteristics when caking is advancing.

Numerical Simulation of Particle Dynamics in a Spiral Jet Mill via Coupled CFD-DEM.

Spiral jet mills are ubiquitous in the pharmaceutical industry. Breakage and classification in spiral jet mills occur due to complex interactions between the fluid and the solid phases. The study of these interactions requires the use of computational fluid dynamics (CFD) for the fluid phase coupled with discrete element models (DEM) for the particle phase. In this study, we investigate particle dynamics in a 50-mm spiral jet mill through coupled CFD-DEM simulations. The simulations showed that the fluid was significantly decelerated by the presence of the particles in the milling chamber. Furthermore, we study the particle dynamics and collision statistics at two different operating conditions and three different particle loadings. As expected, the particle velocity was affected by both the particle loading and operating pressure. The particles moved slower at low pressures and high loadings. We also found that particle–particle collisions outnumbered particle–wall collisions.

Preparation and post-treatment of silver powders for front contact pastes of silicon solar cells

Abstract Corrugated-surface silver powders were prepared for front contact pastes of silicon solar cells. The effects of using different pH controlling agents on the powder diameter, morphology, and conversion of silver ions to silver powders were investigated. Silver powders with wrinkled surface and 100% conversion were prepared, and ground by using spiral jet milling and tumbling ball milling, respectively. Silver powders ground by using spiral jet milling had better size distribution, higher tap density, and corrugated surface, the tap density of silver powders ground by using spiral jet milling was 6.52 g cm–3. The silver powders were used to prepare front contact pastes of silicon solar cells, the aspect ratio of printed gridlines was 0.34.

Analysis of hold-up and grinding pressure in a spiral jet mill using CFD-DEM

A spiral jet mill was simulated using Discrete Element Method modelling and Computational Fluid Dynamics. The particle behaviour and fluid motion were analysed as a function of hold-up and grinding pressure. Particle collision energy was predicted to be prevalent along the bed surface and in front of the grinding jets, as shown through the collision data recorded. The bed itself affects the fluid flow field, as momentum is transferred to the particles. Increasing the grinding pressure does not result in a proportional increase in the kinetic energy of the particle system, as the high pressure jets begin to penetrate the bed with greater ease. The particle bed moves as ‘plug-flow’, with the layers of the bed closest to chamber wall.

Analysis of grinding in a spiral jet mill. Part 1: Batch grinding

Jet milling is widely used in several industrial applications to produce fine particles with a narrow size distribution. We studied by means of experiments, the influence of grinding pressure, holdup and milling time on the performance of a spiral air jet-mill operating in a batch mode, with respect to the particles. The experimental results indicated that a uni-modal size distribution of feed particles yields trimodal particle size distributions. The data for variation of the mean particle size and specific surface area with energy supplied collapsed to a curve for all the cases studied, indicating that mean size is primarily dependent on the energy supplied. A population balance model for the dynamics of the batch milling process, based on empirical breakage functions is developed, which describes the experimental results quite well. The form of the breakage functions provides an insight into the mechanisms of breakage of particles.

Ejector jet mill with external pressure

Jet mills are used to produce fine products in many industries. Spiral jet mills and fluidized bed jet mills are widely used. They differ in that the destruction of particles occurs as a result of the abrasion process. The use of impact ejector jet mills is limited by a relatively low consumable concentration of material. When the consumable concentration of the material increases the acceleration speed of particles and the material grinding degree decrease. To eliminate this disadvantage a new method and design of an ejector jet mill for fine grinding of bulk materials has been developed (patent of Russian Federation No. 2711252). The technological process occurs at excessive external pressure of the ejected gas. It is shown that it is feasible to increase the pressure at the beginning of the acceleration tube when the pressures ratio of the working and secondary gas is higher than the critical one. It increases the consumption concentration of bulk material and the acceleration speed of crushed particles. This allows reducing the specific energy consumption and increasing the grinding degree. Experimental studies have confirmed an increase in the consumption concentration by 1.6–1.9 times and an increase in the grinding degree by 1.3–1.7 times compared to a typical ejector jet mill.