Fluidization Of Powders Research Articles

Stirrer design for improving fluidization of cohesive powder: A time-resolved X-ray study

Stirring has been recognized in the literature as a promising technique for facilitating fluidization of cohesive powders, via inputting additional energy to counteract interparticle forces. However, the influence of operating conditions and stirrer configurations on flow behavior remains largely unknown, which impedes the practical implementation of stirred fluidization. Utilizing X-ray imaging, this research demonstrates that stirring enhances fluidization in cohesive micron-silica powder (Sauter mean diameter ▪) by collapsing the powder packing structure, and transitioning channeling beds into bubbling states. Comb-like configurations featuring fewer stirrers and blades, placed in the bottom region, have shown to be highly effective. Excessive stirring can lead to air pockets and a compacted phase of particles on the column walls, undermining the interaction between particles and stirrers. Additionally, the experiments show that maximizing the sweeping coverage, employing complex asymmetrical configurations, and avoiding tortuous gas pathways are preferable.

Optimizing the surface modification of cohesive polyethylene powders in a vibrated plasma-spouted bed: Exploring agglomerate size impact on coarser particle addition mechanism

Ultrafine polymer powders have garnered attention owing to their superior physical properties and reactivity. Nonetheless, the cohesive nature of these powders notably impedes efficient plasma surface modification, thereby limiting potential applications. The effects of optimizing the fluidization of cohesive powders on plasma treatment within a plasma-spouted bed were investigated in a prior study, wherein surface modification was significantly improved by incorporating coarser particles and vibration. However, the optimal conditions and mechanisms by which adding coarser particles to a vibrated plasma-spouted bed contributes to this enhancement remain unelucidated. This study entailed an investigation of the influence of gas flow rate, agglomerate properties, and plasma distribution in optimizing the wettability modification of ultrafine powders. Results indicate that increased gas flow rate, coarser particle size, and quantity lead to the formation of smaller, more uniform-sized agglomerates. Furthermore, the contact angle of the treated powder demonstrated a linear decrease with the reduction of average agglomerate size within a suitable gas velocity range, suggesting that enhanced exposure of the powder surface to plasma contributes to the optimization of plasma treatment. However, high-gas velocity may trigger particle entrainment and diminish surface modification, as evidenced by the limited plasma distribution primarily at the bottom of the reactor.

Time-resolved X-ray study of assisted fluidization of cohesive micron powder: On the role of mechanical vibration

Mechanical vibration has been broadly used to assist fluidization of cohesive powders, because of its capability to disrupt gas channels and agglomerates. However, the improvement reported in literature is mostly deduced from bulk response and ex-situ measurements, whereas the induced fluidization behavior and underlying physics remain largely unexplored. In this work, the fluidization behavior of micron-sized cohesive silica (Sauter mean diameter D32 = 7.9 μm) has been investigated experimentally under vibration of varying conditions. X-ray imaging was carried out to directly capture the temporal evolution of system hydrodynamics, and identify in-situ powder stratification, bubbling and channel formation. The study demonstrates that vibration effectively collapses gas channels, yet facilitates powder stratification and compaction, therefore developing three distinctive flow regions inside the bed with different fluidization states. Consequently, common measurements, such as pressure drop and bed expansion, tend to overestimate the improvement. In addition, increasing frequency, from 10 Hz to 30 Hz, is observed to increase the number of bubbles by 60 %, whereas a large amplitude (e.g., 2 mm) leads to a 10 % compaction in the top flow region.

Effects of nano-TiO2 particles addition on fluidization of flaky fluorophlogopite powder for the CVD preparation of pearlescent pigments

Effects of nano-TiO2 particles addition on fluidization of flaky fluorophlogopite powder for the CVD preparation of pearlescent pigments

Minimum fluidization velocity and reduction behavior of combusted iron powder in a fluidized bed

The fluidization and reduction behavior of micron-sized iron oxide powder, produced by iron combustion, is studied in a lab-scale cylindrical fluidized bed. The minimum fluidization velocity umf is found to stabilize above normalized static bed heights of 0.5 H/D (static bed height divided by the bed diameter). umf is measured as a function of temperature between 280 and 860 K for both H2 and N2 as fluidizing gas. The experimental results start to deviate from the Ergun correlation at temperatures above 560 K, both for N2 and H2. A new correlation, taking the cohesive inter-particle solid bridge force into account, is proposed in this work to predict the minimum fluidization velocity at high temperature. Reduction experiments are carried out for a total time of 5 h at constant excess velocity with 50, 75 and 100 vol% of H2 and temperatures between 623 and 823 K. Gradual defluidization occurs when the operating temperature exceeds 800 K. A maximum reduction degree of 61% is obtained at 807 K and 100 vol% H2.

Simulation of Fluidization Quality for Various Reduced−Gas Composition and Agitation Speed Circumstances in a Gas-Solid Fluidized Bed with an Inclined Agitator

Blast furnace ironmaking is one of the most serious carbon dioxide emission processes. To reduce energy consumption and CO2 emissions, fluidized bed ironmaking technology with hydrogen as a reducing agent has attracted more and more attention. An inclined agitator was added to the fluidized bed reactor to address the sticking issue in the conventional fluidized bed ironmaking process. In this research, numerical simulation was used to examine the impacts of reducing gas composition and agitation speed on the gas-solid fluidization quality in the cold fluidization of iron ore powder in the fluidized bed with an inclined agitator. The results indicate that the fluidization effect of iron ore powder is better when the volume ratios of H2 to CO and H2 to N2 are 1:1. Under the intensive shear action of the agitator, the standard deviation of pressure drop constantly decreases with the increase in agitation speed, and the decreasing range is smaller and smaller. The fluidization state of the iron ore powder particles in the bed stabilized when the agitation speed reached 160 rpm.

ХИМИЧЕСКОЕ ОСАЖДЕНИЕ ИЗ ГАЗОВОЙ ФАЗЫ ПИРОУГЛЕРОДНЫХ ПОКРЫТИЙ НА ПОРОШКАХ В ПСЕВДООЖИЖЕННОМ СЛОЕ. I. АППАРАТУРА, ПСЕВДООЖИЖЕНИЕ

A laboratory setup for chemical vapor deposition (CVD) at reduced pressure on powder of medium particle size in a fluidized bed (reactor load of 50 g of substrate) was described. Calculations of critical points for the onset of fluidization and entrainment of particles for various gases (Ar, C3H8, C4H10) at a temperature of 20–1000 °C under low vacuum (pressure of 5 kPa) were performed. Model experiments were carried out on the fluidization of corundum powder (granularity of ~300 μm) in an argon flow, as well as in the propane-butane mixture in the absence of CVD. The dependences of the hydrodynamic mode of fluidization on the nature of fluidizing gas, temperature and pressure were analyzed, which make it possible to plan the process of coating deposition itself.

Effect of high stirring speed on the agglomerate behaviors for cohesive SiO2 powders in gas fluidization

The effects of superficial gas velocity and mechanical stirring speed on the precise regulation of flow regimes for cohesive SiO2 powders (mean diameter is 16 μm) were experimentally investigated in a stirring-assisted fluidized bed. The results showed that compared with the agglomerates formed in the non-assisted fluidization of cohesive SiO2 powders, the introduction of mechanical stirring could effectively reduce the size of agglomerates and well disperse the agglomerates during fluidization. The best regulation range of agglomerate particulate fluidization can be achieved at 600 rpm when agglomerate sizes were reduced to below 200 μm. Further investigation based on the operational phase diagram revealed that transformations of flow regimes were dominated by both stirring speed and gas velocity. The stirring applied enlarges the operational range of agglomerate particulate fluidization (APF) with a delayed onset of bubbling for cohesive particles. However, the exorbitant speed increases the collision velocity and contact area between small agglomerates, which results in the formation of unstable agglomerates and the whirlpool of powder.

Effect of Intake position on powder fluidization and conveying characteristics in powder supply device

In this work, a novel built-in intake channel powder supply device was developed for the piston-driven powder fuel feeding system, and a multi-physical coupling model of the gas-powder-moving wall was established using the User Defined Function. A numerical study of powder fluidization and conveying characteristics in a novel powder supply device was presented by using a two-fluid model, and the effects of different intake positions on the flow characteristics in terms of dense gas-solid two-phase in the powder supply process were studied. The results show that the gas phase region is mainly distributed around the intake channel. The powder outlet flow rate fluctuation and the powder layer (εp = 0.1) area peak decreased by 36.6% and 62.5%, respectively, when the intake position is moved forward from 153.9 mm to 172.2 mm in the axial. The area-averaged gas velocity increases and the area-averaged powder volume fraction decreases at the two-phase throat with the forward movement of the intake position. There is a stable stage of the pressure change in the powder storage tank and in the delivery pipeline when the intake channel is arranged at 153.9 mm in the axial, which is more beneficial to the stable conveying of powder.

Influence of structural parameters on fluidization effect of typical fluidization unit of metal powder fuel

The metal powder fuel supply system is a critical technology for achieving multiple starts of a solid rocket engine. The supply system has a direct impact on the performance of the engine, which is one of the main problems to be solved. Therefore, the Eulerian continuous medium method is used to research the influence of structural parameters on fluidization effect of typical fluidization unit of metal powder fuel. The influence of the angle between the inlet of fluidization gas and the powder storage tank and the outlet diameter of the fluidization unit on the response characteristics and stability of the powder supply is investigated. The distributions of metal powder in the storage tank, fluidization region and outlet pipe are analyzed. From the results, it is concluded that the fluidization unit with an angle of 40° to 45° takes less time to reach a steady supply state. The outlet mass flow rate oscillates after the outlet diameter is 7 mm, and the oscillation frequency is 12 Hz. When the average mass flux of the powder at the outlet of the powder fluidization unit is 10610.32 kg/m2·s, a suitable tank pressure drop can sustain the powder fluidization unit.

Gaseous fluidization of short fibers and powders, influence of temperature and pressure

The fluidization of short Hi Nicalon S fibers was investigated before considering CVD coatings with controlled composition and thicknesses. The fluidization of a short fiber batch alone being delicate and not reproducible, the study consisted in comparing the hydrodynamic behavior of a powder alone, to that of a short fiber/powder mixture. The fluidization behavior of the particle beds was studied by following their pressure drop as a function of pressure and temperature. The minimum fluidization velocity (Umf) was evaluated at room temperature (Tamb) at different reduced pressures, and at 200 mbar as a function of temperature. The results are in good agreement with the theoretical equations. At low pressures and Tamb, Umf increases rapidly. In contrast, Umf varies only slightly with temperature. While the pressure does not seem to affect the fluidization behavior of the powder alone, it displays a clear optimum at 200 mbar for the short fiber/powder mixture.

Improvement on fluidization and reduction of ultrafine CuO powders with the assistance of iron microspheres

Fluidization and reduction behaviors of ultrafine CuO powders with the assistance of iron microspheres are investigated. The ultrafine CuO powders that belong to Group C particles are difficult to fluidize due to the strong interactions between particles. However, robust fluidization is achieved with the addition of iron microspheres and the Cu products after the reduction reaction can be completely separated by using a magnetic field. Furthermore, the difference of improvement on fluidization with the assistance of iron microspheres between cold state and reaction state at high temperatures is revealed in the view of interactions between particles. This approach to enhance fluidization during reaction and simplify separation after reaction could be applied to the reaction of other Group C powders.

On the fluidization of cohesive powders: Differences and similarities between micro‐ and nano‐sized particle gas–solid fluidization

AbstractThe fluidization of cohesive powders has been extensively researched over the years. When looking at literature on the fluidization of cohesive particles, one will often find papers concerned with only micro‐ or only nano‐sized powders. It is, however, unclear whether they should be treated differently at all. In this paper, we look at differences and similarities between cohesive powders across the size range of several nanometres to 10s of micrometres. Classification of fluidization behaviour based on particle size was found to be troublesome since cohesive powders form agglomerates and using the properties of these agglomerates introduces new problems. When looking at inter‐particle forces, it is found that van der Waals forces dominate across the entire size range that is considered. Furthermore, when looking into agglomeration and modelling thereof, it was found that there is a fundamental difference between the size ranges in the way they agglomerate. Where the transition between the types of agglomeration is located is, however, unknown. Finally, how models are made and agglomerate sizes are measured is currently insufficient to accurately predict or measure their sizes consistently.

Development of an Add-On Device Using 3D Printing for the Enhancement of Drug Administration Efficiency of Dry Powder Inhalers (Accuhaler).

The goal of this study was to develop an add-on device for dry powder inhalers (Accuhaler) via 3D printing to improve drug administration efficiency in patients with limited inspiratory capacity, including young children, the elderly, and those with chronic obstructive pulmonary disease. With salmeterol xinafoate and fluticasone propionate as model active pharmaceutical ingredients (API), the emitted API doses were used to assess the effectiveness of the add-on device. The APIs were quantified by an HPLC assay validated for specificity, range, linearity, accuracy, and precision. The motor power of the add-on device could be regulated to moderate fan speed and the air flow in the assembled device. When 50–100% of the fan motor power of the add-on device was used, the emitted dose from the attached dry powder inhaler (DPI) was increased. A computational fluid dynamics application was used to simulate the air and particle flow in the DPI with the add-on device in order to elucidate the operating mechanism. The use of the add-on device combined with a sufficient inhalation flow rate resulted in a larger pressure drop and airflow velocity at the blister pocket. As these characteristics are associated with powder fluidization, entrainment, and particle re-suspension, this innovative add-on device might be utilized to enhance the DPI emitted drug dose for patients with low inspiratory rates and to facilitate the provision of adequate drug doses to achieve the treatment outcomes.

Suboptimal Inspiratory Flow Rates With Passive Dry Powder Inhalers: Big Issue or Overstated Problem?

The premise that subjects must overcome the internal resistance of a DPI to achieve a peak inspiratory flow rate of 60 L min-1 12 for effective powder fluidization and deagglomeration of inhaled bronchodilators for the treatment of COPD is fundamentally incorrect. This reliance on a 60 L min-1 13 14 minimum flow leads to a significant overestimate of the percentage of patients with suboptimal flow 15 rates, and this criterion should not be used as a biomarker to guide transition of patients to an active 16 device. Alternatively, the minimum threshold energy for effective drug delivery with passive dry 17 powder inhalers (DPI) occurs at peak inspiratory pressures greater than or equal to about 1 kPa, 18 independent of the internal resistance of the device. Most patients can achieve the threshold 1 kPa 19 pressure drop even during periods of acute wheeze.

Capability of the TFM Approach to Predict Fluidization of Cohesive Powders.

The fluidization behavior of cohesive particles was investigated using an Euler–Euler approach. To do so, a two-fluid model (TFM) platform was developed to account for the cohesivity of particles. Specifically, the kinetic theory of granular flow (KTGF) was modified based on the solid rheology developed by Gu et al. J. Fluid Mech.2019. The results of our simulations demonstrated that the modified TFM approach can successfully predict the formation of particle agglomerates and clusters in the fluidized bed, induced by the negative (tensile-dominant) pressure. The formation of such granules and clusters highly depended on the particle Bond number and the tensile pressure prefactor. To evaluate fluidization regimes, a set of simulations was conducted for a wide range of particle cohesivity (e.g., Bond number and tensile pressure prefactor) at two different fluidization numbers of 2 and 5. Our simulation results reveal the formation of four different regimes of fluidization for cohesive particles: (i) bubbling, (ii) bubbling–clustering, (iii) bubble-less fluidization, and (iv) stagnant bed. Comprehensive analysis of the shear-to-yield ratio reveals that the observed regime map is attributed to the competition between the shear stress and yield stress acting on the particles. The obtained regime map can be extended to incorporate the effect of dimensionless velocity and dimensionless diameter as a comprehensive fluidization chart for cohesive particles. Such fluidization charts can facilitate the design of fluidized beds by predicting the conditions under which the formation of particle agglomeration and clustering is likely in fluidized beds.

From laminar to turbulent flow in a dry powder inhaler: The effect of simple design modifications

In order to better understand powder dispersion in dry powder inhaler (DPI) devices, a new powder disperser was designed, which uses flow modifiers to alter powder fluidization behavior so as to physically replicate various flow conditions observed in a range of commercial DPIs. The influence of these modifiers on the performance of the DPI was analyzed for flowrates progressing from laminar (15 L/min) to transitional (30 L/min), and finally turbulent flow regimes (60 L/min) in the device. The aerosol performance of the disperser was measured using a Next Generation Impactor. For flowrate in the laminar regime, powder evacuation from the disperser was generally insufficient (<30%), which was increased to >85% when the device was operated in the turbulent flow regime. In contrast, the highest fine particle fraction (FPF) and lowest throat deposition were achieved when operating in the transitional flow regime. The FPF could be increased further by applying flow modifications such as narrowing the air passage before the powder pocket, inducing localized turbulence (by a grid) near the powder pocket, and by changing the loading position of the powder. Flow modifiers had the most noticeable effect under a laminar flow regime, however, the device operated most efficiently under a transitional flow regime.

Insights into the potential of rheological measurements in development of dry powder inhalation formulations

Study of flow is a key to development of dry powder inhalation formulations. Various static (bulk) and dynamic rheological measurements are used to study different aspects of powder flow and packing. Among rheological measurements, the permeability and the fluidization energy are, conceptually, most relevant to dispersion of dry powder inhalation formulations. The aim of the current study was to test the robustness and the range of applications of the two measurements, among other rheological measurements. To this end, we prepared and studied a series of ternary, carrier-based dry powder inhalation formulations. The formulations were mixtures of coarse-fine excipient (α-lactose monohydrate) blends, with different fine excipient concentrations (0.0–15.0 % w/w), and a spray-dried drug (fluticasone propionate) material. The excipient blends were characterized in terms of morphology, size, crystallinity, and rheological properties. The formulations were evaluated in vitro using a low resistance inhalation device, the Cyclohaler®, and a high resistance inhalation device, the Handihaler®. The study design aimed to complement literature data. Bulk rheological measurements, specifically the bulk density, the compressibility, and the permeability, exhibited satisfactory precision and could demonstrate changes in powder composition and structure. They hold a potential for use as critical material attributes to aid monitoring and optimization of carrier-based dry powder inhalation formulations in quality-by-design systems. On the other hand, dynamic rheological measurements, specifically the basic flowability energy, the specific energy, and the fluidization energy, generally exhibited high variability, which obscured interpretation of the measurements and implied heterogeneous powder structures. The fluidization energy could, nevertheless, convey structural changes taking place during powder fluidization.

Fluidization of lactose carrier powders through normally directed airflow: The effect of recirculation and particle size

This study investigates the fluidization of lactose carriers from a powder bed subjected to a normal force in a channel flow using high-speed imaging, particle image velocimetry (PIV), and high-speed, long-distance microscopy (HS-LDM). Pharmaceutical lactose carriers (LH200 and SV010) with different cohesiveness and fines percentages were examined in this study. Airflow velocities in the range of1.4 m/s and7m/s were tested, corresponding to flow rates ranging from 20 to 100 L/min. The use of HS-LDM in tandem with PIV has enabled measurement of the slip factor between particles and conveying airflow as well as metrics that help to identify dose homogeneity as a function of location in the channel flow.The results indicate a lower slip ratio and a larger change in powder particle size bands percentages along with channel height in the region near the powder bed, because of flow recirculation and higher velocity fluctuation observed in that region.

Elucidating the Effect of Fine Lactose Ratio on the Rheological Properties and Aerodynamic Behavior of Dry Powder for Inhalation.

Dry powder inhaler (DPI) is recognized as the first choice for lung diseases' treatment. However, it lacks a universal way for DPI formulation development. Fine lactose is commonly added in DPIs to improve delivery performance; however, the fine ratio-dependent mechanism is unclear. Therefore, the objective of this study is to explore the influence of fine lactose ratio on DPI powder properties and aerodynamic behavior, and the fine lactose ratio-dependent mechanism involved during powder fluidization and lung deposition. Here salbutamol sulfate was used as a model drug, Lactohale® 206 as coarse carrier, and Lactohale® 300 as fine component; the mixtures were prepared at 1% drug content, with fine content up to 20%. It was shown that with the fine addition, flowability of the mixtures was improved, interaction among particles was increased, and the presence of fines could help to improve DPI's aerosolization performance. When the fines added were less than 3%, the "active site" hypothesis played a leading role. When the added fines were over 3% but less than 10%, fluidization enhancement mechanism was more important. After the added fines reaching 10%, aggregate mechanism started to dominate. However, FPF cannot be further increased once the fines reached 20%. Moreover, the correlations between FPF and dynamic powder parameters were verified in ternary mixtures, and cohesion had a greater impact on FPF than that of flowability. In conclusion, adding lactose fines is an effective way to improve lung deposition of DPI, with the concrete mechanism lactose fine ratio dependent.