Powder discharge from a hopper-standpipe system modelled with CPFD

In this paper, computational particle fluid dynamic (CPFD) modelling approach was used to describe the discharge of a fine glass beads powder from different hopper-standpipe geometries. The comparison between the CPFD predictions and the experimental results in terms of solid discharge rates, surface cone shape during discharge and pressure drops in the standpipe. The comparison allowed to assess on the possibility to use the CPFD modelling approach to simulate the powder flow in the hopper-standpipe system even accounting for the rather complex interactions between the interstitial gas and the particles occurring in the presence of a standpipe. Furthermore, the effect of hopper geometry on powder discharge was investigated with the CPFD model and verified experimentally in some purposely built hoppers. Finally, the relationships between the hopper geometry parameters (hopper outlet diameter and hopper half angle) and the flow parameters (solid discharge rate, height of characteristic surface, particle volume fraction, particle velocity, gas pressure and flow pattern) were obtained.     

Drained Angle of Free-Flowable Powders

The measurement of the angle of repose is a conventional method for estimation of powder flowability. This method is known to have lower reproducibility of results when greater angles of repose are obtained, in particular in the case of cohesive powders. The flowability of free-flowable powders can also be characterized by discharging from a hopper. In a cylindrical flat-bottomed hopper having a central circular orifice, a residual amount of powder remains in the hopper at the end of the discharging procedure. In this work, the size fractions of sodium chloride, sodium citrate, and potassium citrate in the range 0.0315–0.0600 cm were characterized with the bulk density and the mass discharge rate through 0.6–1.2 cm orifices of the cylindrical stainless steel hopper. The mass of the residual powder has been found to be indirectly proportional to the powder discharge rate. A method of the indirect estimation of the drained angle was proposed. The derived equation uses the mass of the residual powder, the powder bulk density, the inner diameter of the hopper, and the diameter of the hopper orifice as the independent variables. In the studied range of variable values, the experimentally obtained drained angles showed significant negative correlation with the mass discharge rate and the volume discharge rate of test powders, while no correlation was found between the drained angle and the mass discharge coefficient of the Beverloo equation. In order to measure the drained angle in the cylindrical hopper having an inner diameter of 4 cm, an orifice diameter equal to 1.0 cm was optimal. Filling of the powder into a hopper in conformity with the standard conditions of bulk density measuring in a graduated cylinder is the basic presumption. Since the drained angle follows the relief of bulk powder during discharge from the cylindrical hopper, it thus describes the powder flowability more comprehensively than the angle of repose to the horizontal. Good reproducibility of results follows the 3-D indirect estimation of the drained angle as well. In order to avoid any residue of powders in the conical hopper at the end of the discharging operation, the wall angle could be larger than the drained angle of the powder in the cylindrical hopper. This is typical for the mass flow of size fractions of free-flowable powders, the drained angles of which are approximately two times greater than their angles of repose.     

Control of the profile of the impurity distribution in epitaxial layers grown from a solution-melt with regulated volume and composition

The possibilities of obtaining linear and nonlinear profiles of the impurity distribution by liquid epitaxy are studied. Analytical expressions are obtained for the profile of the impurity distribution in epitaxial layers grown from solutions-melts with a constant volume and with a varying volume, where a variation in the volume of the basic solution-melt and in the amount of the doping impurity in it is achieved by mixing, to it, an additional saturated solution through the capillary opening. It is shown that in this case the profile of the impurity distribution is determined by the velocity of feed of the additional solution-melt. Comparisons of experimental data with calculated results are presented.     

An investigation into the impact of magnesium stearate on powder feeding during roller compaction

A systematic evaluation on the effect of magnesium stearate on the transmission of a placebo formulation from the hopper to the rolls during screw fed roller compaction has been carried out. It is demonstrated that, for a system with two 'knurled' rollers, addition of 0.5% w/w magnesium stearate can lead to a significant increase in ribbon mass throughput, with a consequential increase in roll gap, compared to an unlubricated formulation (manufactured at equivalent process conditions). However, this effect is reduced if one of the rollers is smooth. Roller compaction of a lubricated formulation using two smooth rollers was found to be ineffective due to a reduction in friction at the powder/roll interface, i.e. powder was not drawn through the rollers leading to a blockage in the feeding system. An increase in ribbon mass throughput could also be achieved if the equipment surfaces were pre-lubricated. However this increase was found to be temporary suggesting that the residual magnesium stearate layer was removed from the equipment surfaces. Powder sticking to the equipment surfaces, which is common during pharmaceutical manufacturing, was prevented if magnesium stearate was present either in the blend, or at the roll surface. It is further demonstrated that the influence of the hopper stirrer, which is primarily used to prevent bridge formation in the hopper and help draw powder more evenly into the auger chamber, can lead to further mixing of the formulation, and could therefore affect a change in the lubricity of the carefully blended input material.     

Characterization of fluctuations in granular hopper flow

We present a 2D discrete modelling of sand flow through a hopper using realistic grain shapes. A post-processing method is used to assess the local fluctuations in terms of void ratio, coordination number, velocity magnitude, and mean stress. The characteristics of fluctuations associated with the four considered quantities along the vertical axis of the hopper and across the entire hopper are carefully examined. The flow fluctuations for coordination number, velocity magnitude and mean stress are all found to take the form of radial waves originating from the lower centre of the hopper and propagating in the opposite direction of the granular flow. Quantitative characteristics of these waves (shape, amplitude, frequency, velocity, etc.) are identified. The fluctuations in void ratio however are not supportive of the observation of density waves in the granular flow as mentioned in some experiments. The possible reasons for this apparent contradiction are discussed, as well as possible extensions of this work.     

Modeling of Powder Blending Using On-line Near-Infrared Measurements

A model to quantify the degree of mixing in pharmaceutical powder mixing operations was developed. The additive volume mixing model is based on the determination of the characteristic volume of agitation for a given blender, which is dependent on process parameters such as the formulation ingredients, the geometry of the mixer, and the batch load. The calculation of this characteristic volume of agitation is based on the determination of the fitted fraction of formulation mixed after the first blender rotation. A variation of this model, denominated the iterative mixing model, was also developed. On-line near-infrared (NIR) measurements were taken throughout the runs to obtain the mixing profile and the dynamics of the powder bed as a function of blender rotations. Studies were conducted at two scales using two different formulations to study and compare the calculated characteristic volume of agitation for each blender-formulation system. This approach elucidates the existing relationship between the characteristic mixing parameters and critical rotations (required rotations to achieve content uniformity) for a given system and represents a step toward scale-up of solids mixing operations.     

A more efficient method for calibrating discrete element method parameters for simulations of metallic powder used in additive manufacturing

Laser powder bed fusion (LPBF) is an additive manufacturing (AM) process that uses a high-power laser to selectively melt metal powder that has been spread, layer-by-layer, to create parts with highly complex features. Because of the strong influence that the powder spreading process has on the final part quality, a better understanding of the powder behavior and its interactions with existing powder layers and the solidified surfaces during this process is needed. Discrete element method simulations (DEM) provide a particle-scale approach capable of examining these mechanisms. While proper calibration of these simulations provides confidence in the quantitative results, the usual calibration process (hopper method) is computationally time intensive. Because of the wide variety of powder material used in LPBF, which will affect the powder spreading process, and because of the large numbers of particles present in only a small volume of powder, a more efficient calibration process was necessary. Use of a new cloud method was shown to make calibrations more tractable and reduce simulation times by up to 89% when compared to a typical hopper method. Similar to previous studies shown in the literature, a reduction in the particle material’s Young’s modulus was also used to reduce simulation times by up to 62%. Both sliding and rolling friction were needed for the DEM angles of repose to match the empirical data because of the non-sphericity of some of the powder particles, which has been quantified. The calibrated parameters resulted in determination of a powder density within 10% and an angle of repose within 1% of the targeted experimental values. These parameters will be used in extensive future DEM simulations of the LPBF powder spreading process. While AM processes were the main motivation for this work, the calibration procedures summarized herein can be extended to other gas-atomized powders used in injection molding and other metallurgical fields, as well as many other granular materials.     

橡胶连续混炼粉料混合均匀性仿真及实验研究

为了提高橡胶连续混炼中混炼胶质量稳定性,实现炭黑等粉体物料精确配比和均匀性混合问题,针对粉体物料在混合和输送过程存在复杂的物理性质,建立了炭黑等混合粉料的球体颗粒模型和Hertz接触力-位移模型,采用EDEM对典型粉体物料混合均匀性进行模拟仿真和粉体物料混合实验,对炭黑等粉体物料在橡胶连续混炼工艺中的混合均匀性进行分析,探求橡胶粉料连续混合和输送机理.研究发现:粉体物料混合仿真与实验测试结果具有较高的拟合性,表明在橡胶连续混炼工艺中可以在保证混合均匀性的前提下实现多粉体混合物的连续称量和输送,同时也验证了运用EDEM数据模拟仿真粉体物料混合的可行性.     

Discharge Characteristics of Polydisperse Powders through Conical Hoppers. Part 1: Predictions for Fine, Granular, Free Flowing Powders

Discharge characteristics of fine polydisperse granular powders of equal-solid density and near-spherical particle shape through a conical hopper were investigated by measuring solid discharge rates of powders. Effects of orifice size of hopper and size distribution of powders on discharge rate were determined by means of experiments conducted for six different sizes of hopper orifice and three different powder types under gravity flow conditions. A new effective mean diameter characterizing polydisperse powders is first introduced and determined from the particle size versus weight fraction distribution of a powder as the size corresponding to 50% cumulative weight fraction. This effective mean diameter was efficiently used in two modified forms of the Beverloo equation to predict discharge rates of polydisperse powders through hopper orifices.     

DEM Applications to Aeolian Sediment Transport and Impact Process in Saltation

Discharge characteristics of fine polydisperse granular powders of equal-solid density and near-spherical particle shape through a conical hopper were investigated by measuring solid discharge rates of powders. Effects of orifice size of hopper and size distribution of powders on discharge rate were determined by means of experiments conducted for six different sizes of hopper orifice and three different powder types under gravity flow conditions. A new effective mean diameter characterizing polydisperse powders is first introduced and determined from the particle size versus weight fraction distribution of a powder as the size corresponding to 50% cumulative weight fraction. This effective mean diameter was efficiently used in two modified forms of the Beverloo equation to predict discharge rates of polydisperse powders through hopper orifices.     

A DEM Analysis of Flow Characteristics of Noncohesive Particles in Hopper

Flow characteristics of material in hoppers, silos, and bins are critical issues for operational stability as well as structural integrity of these units. In this work, flow of noncohesive particles in hopper is studied using the discrete element method (DEM) where each particle is tracked for its position, velocity, and acceleration. Material properties tend to alter during hopper flow due to compaction, expansion, and segregation. These features are difficult to model with a continuum approach. In the first part, material flow patterns are correlated with hopper angle and hopper opening, the two main design parameters. The typical shift from mass flow to funnel flow depending on the hopper angle was successfully simulated. In the second part, the discharge rate of material was quantitatively analyzed as function of hopper design parameters. Beverloo model 1 was tested on these simulated flow rates and it was shown that the simulated flow rates follow the model for this specific granular system. However, the DEM analysis was also able to demonstrate the failure of the traditional Beverloo model in the restricted flow regime. Simulated flow rates also follow the empirical correlations with hopper angle as stated in literature. DEM simulations were validated with experimental data for both material flow pattern and discharge rates.     

Predictive Stress Tests in the Scale-Up of Capsule Formulations

In early development, supplies of bulk active are limited and capsule formulations are developed on a small scale. However they should be suitable for scale-up. In this report, the Turbula T2C is shown to mimic the prolonged stirring and stressing of powder blends in the large hopper of a dosator type machine, e.g. Zanasi LZ64. The degree of mixing affects the lubricity and wettability of capsule blends containing magnesium stearate and stressing powder blends in a Turbula T2C highlights changes in blend properties which occur on scale-up. Measuring tapped bulk density, wettability and disintegration of stressed blends identifies robust formulations which are unaffected by long “lubrication” times and scale. Changes in blend properties are influenced more by shearing energy than the extent of mixing     

SIZE SEGREGATION DURING MASS FLOW—EFFECT OF DEPOSITION METHOD AND BIN SIZE

Size-Segregation of granulated sugar during discharge from hopper bins was studied, with respect to the effect of bin size and bin fill method. Particle size distributions (PSDs) were analyzed from large and small mass flow hopper bins, using three different fill methods. Spoon-by-spoon deposition was used as a control, whereas funnel fill and inverted cone deflector fill were used to model industrial fill methods. Samples were taken during the discharge of the bins and PSDs were analyzed. For all three bin fill methods and both bin sizes, the PSDs were within the 95% confidence interval of the original, in bag, sugar PSD. The worst case scenario occurred at the 250 μm sieve size, where the greatest percent difference from original PSD value was observed. At 50% discharge for the 250 μm sieve the small (large) bin showed a maximum percent difference for spoon-by-spoon, funnel and inverted cone deflector fill of 21(4), 10 (9) and 6 (28), respectively. For the small and large bins, the largest percent differences of 49 and 37, respectively, occurred at 40% and 20% material discharged, respectively. The bin fill method did not affect the PSD significantly based on 95% confidence interval.     

Predictive Stress Tests in the Scale-Up of Capsule Formulations

Abstract

In early development, supplies of bulk active are limited and capsule formulations are developed on a small scale. However they should be suitable for scale-up. In this report, the Turbula T2C is shown to mimic the prolonged stirring and stressing of powder blends in the large hopper of a dosator type machine, e.g. Zanasi LZ64. The degree of mixing affects the lubricity and wettability of capsule blends containing magnesium stearate and stressing powder blends in a Turbula T2C highlights changes in blend properties which occur on scale-up. Measuring tapped bulk density, wettability and disintegration of stressed blends identifies robust formulations which are unaffected by long “lubrication” times and scale. Changes in blend properties are influenced more by shearing energy than the extent of mixing     

DEM simulation for optimal design of powder mixing in a ribbon mixer

A ribbon mixer is often employed in powder mixing in a wide range of engineering fields. The structure of the ribbon mixer is extremely complicated. This structure makes it difficult to understand the mixing mechanism by experimental approaches due to problems related to accurate sampling. At present, the mixing mechanism in the ribbon mixer is empirically identified as convection, despite a lack of precise assessment. Additionally, experimental investigations to find the optimal design of the ribbon mixer have not been sufficiently conducted because of its prohibitive cost. As such, there is a lack of sufficient discussion concerning the design for better mixing in the ribbon mixer. Numerical technologies represent a promising approach for solving the aforementioned problems. Significant improvements in computer hardware have enabled numerical models such as the discrete element method (DEM) to be positively employed in powder mixing. In the current study, an identification approach is developed for convective mixing, and besides, the study explores an effective parameter for better mixing in the ribbon mixer using the DEM. A swept volume measurement approach due to paddle movement is newly developed to identify the main mixing mechanism as convection. Sensitivity analyses are performed to find an effective parameter for better mixing. Through the sensitive analyses, the blade width is indicated as an important factor for achieving better mixing. Moreover, this study shows that the relationship between the swept volume and mixing index remains, even if the paddle width changes. Thus, the swept volume measurement method is revealed as useful for identifying the mechanism as convection in the ribbon mixer. Thus, not only novel finding regarding the blade width for better mixing but also the development of an approach for identifying convective mixing in the ribbon mixer is presented herein. Incidentally, convection being the dominant mechanism is consistent with the novel finding regarding blade width achieving better mixing.     

SIZE SEGREGATION DURING MASS FLOW—EFFECT OF DEPOSITION METHOD AND BIN SIZE

ABSTRACT

Size-Segregation of granulated sugar during discharge from hopper bins was studied, with respect to the effect of bin size and bin fill method. Particle size distributions (PSDs) were analyzed from large and small mass flow hopper bins, using three different fill methods. Spoon-by-spoon deposition was used as a control, whereas funnel fill and inverted cone deflector fill were used to model industrial fill methods. Samples were taken during the discharge of the bins and PSDs were analyzed. For all three bin fill methods and both bin sizes, the PSDs were within the 95% confidence interval of the original, in bag, sugar PSD. The worst case scenario occurred at the 250 μm sieve size, where the greatest percent difference from original PSD value was observed. At 50% discharge for the 250 μm sieve the small (large) bin showed a maximum percent difference for spoon-by-spoon, funnel and inverted cone deflector fill of 21(4), 10 (9) and 6 (28), respectively. For the small and large bins, the largest percent differences of 49 and 37, respectively, occurred at 40% and 20% material discharged, respectively. The bin fill method did not affect the PSD significantly based on 95% confidence interval.     

Electrode Characteristics of MmNi_5-based Alloys for Nickel-Metal Hydride Batteries

Negative electrodes of the Ni-metal hydride battery were made from hydrogen storage alloy Mm0.9Ti0. 1Ni3. 9Mn0.4Co0.4Al0.3 mod fied by coating with Ni or mixing with Co powder. The cell volume expansion of hexagonal structure was about 12 % after coating with 11 % Ni on the alloy Surface,When this alloy was mixed with Co powder. the discharge capacity and the utilization efficiency of the hydrogen storage alloy increased. When the alloy was coated with 11 wt-% Ni and also mixed with 10 wt-% Co powder. the capacity decay for a small sealed cylindrical cell (AA size. 1 Ah) was only about 4 % after 200 cycles     

Performance evaluation of In-Deep Class Storage for Flow-Rack AS/RS

This article presents a new storage-retrieval method called In-Deep Class Storage, designed for Flow-Rack AS/RS. Class-based storage is a well-known method that has an extensive literature; our method is based on the fact that it is more efficient to dedicate the front layers of each bin to the class of the most popular items rather than dedicating whole bins close to the drop-off station. Clearly, this idea is not trivial to implement due to the dynamic behaviour of such racks. Thus, two separate algorithms have been defined, one for storage and one for retrieval, enabling dynamic use of our approach, with the only hypothesis of a Pareto distribution of item demand. This article presents a simulation study designed to compare the performance of random storage and retrieval with the use of the algorithms. This study shows a significant improvement of the expected retrieval delay, the main performance indicator selected for the study.     

Experimental and numerical investigations on the heat production and thermal storage characteristics of rapid preparation amorphous powder activated coke

The heat production and thermal storage characteristics of rapid-preparation amorphous powder activated coke (RAC) were investigated. RAC was prepared by using a drop-tube reactor system. The natural oxidation characteristics of RAC were studied through combined TG–FTIR analysis and temperature-programmed experiment. Experimental results showed that CO and CO₂ were the main oxidation products of RAC in air, and that the oxidation reaction was in accordance with the Arrhenius equation and law of mass action. Thermal storage characteristics were studied through computational fluid dynamics simulation. The maximum excess temperature θ_max increases linearly with the increase of the initial temperature. The concentration fields of the products show that CO₂ is mainly concentrated in the upper part of the coke bin, and the CO generated by CO₂ at high temperature is mainly concentrated in the central part of the coke bin.     

Quantifying and reducing powder shear sensitivity when manufacturing capsules with lubricants

The purpose of this work was to develop a methodology that quantifies the extent of shear induced during an encapsulation process and show how formulation composition and manufacturing process designs can be changed to reduce the negative impact on drug product quality attributes. The powder feed system used in a dosing disc type pharmaceutical capsule filling machine induced additional shear of the powder prior to slug formation. The shear occurred both in the hopper portion, via the rotation of the feed auger and impeller, and in the powder bowl via the tamping pin agitation and/or shear against the stationary surfaces such as the powder level scraper. The extent of shear was quantified to assess the impact of further dispersing the hydrophobic lubricant, magnesium stearate, in both active and placebo formulations. Stratified samples over the course of the encapsulation run showed suppression in the drug dissolution profiles and decrease in the interparticulate tensile strength of the encapsulated product. The amount of shear (duration and rate) induced during the encapsulation unit operation can be much greater than that from typical bin blending operations and therefore requires consideration during product design and scale-up to ensure product robustness.