Pickup Velocity Research Articles

Tailoring the flow properties of inhaled micronized drug powders by atomic and molecular layer deposition

For dry powder inhaled formulations, good flow behaviour is vital in re-dispersing the powder. However, inhaled drug powders with a particle size below 10 µm are classified as highly cohesive materials with poor flow characteristics. Here we demonstrate how to alter the flow properties of micronized budesonide powders by depositing different materials (organic, inorganic, and hybrid organic–inorganic) in the forms of nanoscale films onto the drug particles using atomic/molecular layer deposition (ALD/MLD) coatings. The angle of repose (static) and pneumatic delivery measurements were performed to access the flow characteristics. The flowability can be effectively improved with the growth of inorganic nanofilm (SiO2, TiO2, or Al2O3) via ALD and hybrid nanofilm (titanicone) via combined ALD-MLD coating. This improvement is reflected by the decrease in the angle of repose and minimum pick-up velocity (Upu), as well as promoting the pneumatic delivery of a much larger amount of drug powders after ALD or hybrid coating. In contrast, the organic PET coated budesonide via MLD exhibits comparable poor flow characteristics as the uncoated budesonide. Rather than being transported in individual particles, the uncoated or PET-coated budesonide powders are pneumatically delivered in form of complex clusters with a size of over 500 μm, whereas the ALD budesonide is dispersed in form of small agglomerates (<100 μm). Despite the difference in agglomerate size, entraining behaviors of all samples agree well with the prediction of Kalman’s pick-up Zone I correlation. The inorganic nanofilm deposited via ALD alters the surface chemistry to reduce the inter-particle forces measured by atomic force microscopy, giving rise to an improved drug delivery performance. Nanoscale surface modification of dry powder particles has good potential for inhaled drug delivery enhancement.

Comparison of Axial Flow and Swirling Flow on Particle Pickup in Horizontal Pneumatic Conveying

Pneumatic conveying is widely used in coal mining. As the lowest conveying velocity of materials, the pickup velocity is the key to the study of gas–solid two-phase flow. In this study, the pickup velocity of pebble particles was experimentally investigated. When the particle size is 3–9 mm, the airflow velocity was found to suitably describe the results as a function of the pickup velocity and have a high correlation. When the swirl number is 0.2, the optimal swirl number was found for which the highest particle pickup ratio was observed. Based on four different methods, namely, visual observation, mass weighing, coefficient of difference analysis, and determination of the peak-average ratio of the pressure drop in the flow field to measure the pickup velocity of the spraying material, the results showed that the accuracy of the particle pickup velocity obtained through visual observation was the lowest, and when the mass–loss rate of the particle was selected as the measurement index of the pickup velocity, the accuracy was the highest. The results will help to realize the long-distance transportation of spraying materials in inclined roadway under the shaft.

Simple pick-up velocity measurement procedure and defining non-settling particles using a rheometer

The pick-up velocity is a threshold velocity that is considered when designing hydraulic or pneumatic conveying systems. Defining the conveyed particles as ‘settling’ or ‘non-settling’ affects the calculation method of the pressure drop over a hydraulic conveying system. Rheometers are commonly used to measure the dynamic viscosity of liquids and suspensions. In this work, a unique method of using a rheometer is presented. The method enables simple measurement of the pick-up velocity by increasing the rotational speed of the rheometer. In addition, characterizing the particles as non-settling is achieved by decreasing the rotational speed. The results of this work correlate well with previously published results, confirming that these two parameters can be found by conducting very simple and quick measurements.

Sliding angle of repose and pickup velocity of chosen types of chipped wood

Sliding angle of repose and pickup velocity of chosen types of chipped wood. The report presents the results of the study of conditions sufficient for the motion or immobility of a layer of chipped wood on an inclined plane of sliding and the value of the air velocity in a horizontal duct for lifting or settling a layer of particles of bulk material. When performing the work, special laboratory units were used with adjustment of the angle of inclination of the sliding plane and air velocity in the pipeline. The results of experimental studies can be used to solve issues of transportation, bunkering and storage of some common species and types of chipped wood (sawdust, shavings, sanding dust).

The effect of particle initial charge on minimum pickup velocity (Upu) in pneumatic conveying

Pneumatic conveying experiments involving monodisperse and binary-size mixtures of glass beads with charges in the range of −10 to 10 nC have been carried out. The mass loss method was adopted, with the minimum pickup velocity (Upu) determined as the minimum velocity at which entrainment occurred. Similar to previous studies on minimum fluidization velocity, the Upu increased with particle initial charge for the positively charged particles (0–10 nC). Surprisingly, however, negatively charged particles exhibited an opposite trend such that the Upu decreased with charge magnitude. Therefore, for the particle initial charge range investigated (−10 to 10 nC), Upu increased monotonically with particle initial charge, and the correlations available (Kalman et al., 2005; Tay et al., 2012) mis-predicted Upu by up to 10 % for monodisperse systems and up to 40 % of binary-size systems. This underscores the necessity to account for particle initial charge in such correlations, particularly for polydisperse particle systems.

Experimental study on the horizontal dense-phase pneumatic conveying of sawdust

In some specific situations, solid particles are pneumatically conveyed, requiring a relatively high accuracy for the pipeline pressure drop, the mass flow rate of the solid particles, and the superficial velocity of the carrier gas. At present, sawdust is conveyed in a steel pipeline. To determine the flow characteristics in the pneumatic conveying of sawdust, the influence of the Froude number (Fr) on the solid friction factors (λs, λz), the change in the solid mass (W) over time (T), and the variation tendency of the carrier gas mass flow rate (Q) with the solid mass flow rate (w) are analyzed. For different solid–gas ratios (μ), as Fr increases, λs decreases, and the influence of Fr on λs is greater than that of μ. As Fr increases, μ decreases. The superficial velocity (ua) increases with a more obvious change in the solid mass over time. When the superficial velocity is 5 m/s, the experimental data agree well with the numerical fitting data. While the mass flow rate of the solid is 0.333 kg/s, the required mass flow rate of the carrier gas is minimal, at 0.00269 kg/s, with a minimum pickup velocity of 4.26 m/s.

Model Predictive Control for Real-Time Point-to-Point Trajectory Generation

The problem of planning a trajectory for robots starting in an initial state and reaching a final state in a desired interval of time is tackled. We propose an approach based on model predictive control to solve the problem of point-to-point trajectory generation for a given final time. We discuss various choices of models, objective functions, and constraints for generating trajectories to transfer the state of the robot, while respecting physical limitations on the motion as well as fulfilling computational real-time requirements. Extensive simulation results illustrate the use of the approach, and experiments on an industrial robot in a challenging ball-catching task show the effectiveness of the approach also in demanding scenarios with real-time constraints on the computation. Note to Practitioners —This paper was motivated by the problem of generating movements to transfer a robot from its current state to a new position and velocity at a certain time, when the target state and the final time may require correction at a high rate. For example, for picking small objects from a conveyor belt with a variable feed rate, an off-line planning would fail, since the motion has to be adjusted as soon as the speed is changed. Under the assumption that the desired pickup position and velocity and arrival time can be predicted, the approach in this paper is applicable. The movements can be optimized, for example, for energy efficiency or for reduction of vibrations in the robot. We discuss how to mathematically express the desired performance criteria and other requirements on the motion, such as not violating a maximum joint speed. Quick reactions to sensor inputs are computationally demanding. Thus, we limit ourselves to a class of motion-generation problems that lends itself to numerical optimization. Additionally, we save computation power by gradually refining the motion.

Prediction of lump coal particle pickup velocity in pneumatic conveying

To reduce the airflow velocity and improve the pneumatic conveying performance of lump coal particle, the pickup process and pickup prediction of lump coal particles with 5–15 mm diameters are firstly studied in this paper. The pickup velocity of lump coal particles were determined by the weight loss method and observed by a high speed camera. The results show that the pickup mechanism, the pickup process, and the variation in the weight loss curve of the lump coal particle are similar to the results of Geldart D particles and Geldart B particles. Notably, two observations are worth highlighting: (1) the pickup of lump coal particles is determined by the critical motion, namely, initial shaking and rolling, which are mainly affected by the disturbance of airflow, the disturbance of particle impact, and the disturbance of unstable-support; and (2) the K & R model has a favorable adaptability to large lump coal particles, and an exponential equation, based on the foundation of the K & R model and taking the dimensionless particle size into account, is employed to predict the pickup velocity of lump coal particles. The prediction deviations agree well with the experimental results.

Influence of swirling intensity on lump coal particle pickup velocity in pneumatic conveying

Pickup velocity, defined as the airflow velocity requirement of the initial movement of solid particles, is the well-recognized minimum conveying velocity required of a pneumatic conveying system. To reduce the airflow velocity, the influence of swirling intensity on lump coal particle pickup velocity was studied via experimental measurements. The pickup velocity of lump coal particle was determined by the weight loss method and the whole process was recorded by a high-speed camera. Initially, a side inlet guide vanes swirling generator was developed and used to measure the effect of swirling airflow. The impact of the swirling intensity was discussed and regressed, considering the tangential flow rate, the total inlet airflow rate, and the measurement position. Subsequently, the pickup velocities of 5 to15 mm lump coal particles in axial and swirling flow field were separately determined. In addition, a normative gradual change of tangential flow rate was utilized to examine the pickup velocity variation with swirling intensity. Two points in particular are worth highlighting: (1) the lump coal particle pickup process is prone to rolling up from coal particle bed fore-end, rather than the locally layer-by-layer peeling off in axial flow field; and (2) the pickup velocity of lump coal particle first increases and then decreases with swirling number, and a cubic polynomial function has favorable adaptability to fit the relationship between the lump coal particle pickup velocity and swirling intensity. The fitting results show good agreement with the measurements, with the fitting errors being <3%.

Minimum pickup velocity: The transition between nano‐scale and micro‐scale

The transport of nano‐scale particles has become increasingly important, but the knowledge base available is limited. This study aims to bridge the knowledge gap between the nano‐ and micro‐scales for pneumatic conveying. A key parameter is the minimum pickup velocity (Upu), which is the minimum fluid velocity required to initiate motion in a particle originally at rest. The Upu values of nine alumina particles with particle diameters (dp) ranging from 5 to 110,000 nm were determined using the weight loss method, then compared against the established pickup Zones (analogous to the Geldart Groups). Results indicated that: (1) Upu varied non‐monotonically with increasing dp, thus revealing the missing link between the nano‐ and micro‐scales; (2) the intermediate particle diameters surprisingly did not agree with any pickup Zone; (3) Zone III (analogous to Geldart Group C) is inadequate for all the nano‐scale particles, so new boundaries and a new Zone are proposed. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1512–1519, 2017

Microtransfer printing of metal ink patterns onto plastic substrates utilizing an adhesion-controlled polymeric donor layer

We propose a method for transfer-printed electrode patterns onto flexible/plastic substrates, specifically intended for metal ink that requires a high sintering temperature. Typically, metal-ink-based electrodes cannot be picked up for microtransfer printing because the adhesion between the electrodes and the donor substrate greatly increases after the sintering process due to the binding materials. We introduced a polymeric donor layer between the printed electrodes and the donor substrate and effectively reduced the adhesion between the Ag pattern and the polymeric donor layer by controlling the interfacial contact area. After completing a wet-etching process for the polymeric donor layer, we obtained Ag patterns supported on the fine polymeric anchor structures; the Ag patterns could be picked up onto the stamp surface even after the sintering process by utilizing the viscoelastic properties of the elastomeric stamp with a pick-up velocity control. The proposed method enables highly conductive metal-ink-based electrode patterns to be applied on thermally weak plastic substrates via an all-solution process. Metal electrodes transferred onto a film showed superior electrical and mechanical stability under the bending stress test required for use in printed flexible electronics.

Impact of particle diameter, density and sphericity on minimum pickup velocity of binary mixtures in gas-solid pneumatic conveying

The impacts of particle diameter (dp), particle density (ρp) and particle sphericity (φ) on the minimum pickup velocity (Upu) of binary mixtures of Geldart group B particles were investigated. Three types of binary mixtures were tested, whereby the two constituents vary in (i) only dp (i.e., binary-size), (ii) only ρp (i.e., binary-density), and (iii) both dp and ρp (i.e., binary-size-density). Notably, there is a lack of data on the pickup characteristics of the latter two types of binary mixtures, although behavioral differences are acknowledged. The minimum pickup velocity, Upu, was experimentally determined by the weight loss method and also derived using a force balance model developed here. The key results were: (1) dp exerts a more dominant influence on Upu than ρp; (2) particle sphericity (φ) has a non-negligible impact on Upu; and (3) a drag and frictional force balance analysis accounting for particle sphericity gives reasonable predictions of Upu, which in turn provides a mechanistic insight on Upu.

Experimental flow characterization of sand particles for pneumatic transport in horizontal circular pipes

This work presents an experimental study carried out to simulate characteristics of turbulent air-sand particles flow through transparent horizontal pipes with various flow conditions. Experimental analysis focuses on the determination of critical pickup velocity of the solid particles from the horizontal sand layers. Mainly the effects of layer height and pipe diameter on the pickup velocity are investigated. Critical pickup velocity is determined by extrapolating the weight loss curves plotted as a function of corrected velocity above the sand layer. Experimental results show significant effects of layer height and pipe diameter on the pickup velocity. Saltation velocity and dune formation mechanisms are also discussed. Critical pick up velocity of solid particles is found to increase with increasing blockage ratio and pipe diameter. Inclination angle for larger sand bed heights caused leading edge effect on air flow entering the reduced cross sectional area above the layer. Sand particles pickup rate is found to decrease with time as a consequence of decreasing layer height. Experimental results have been correlated and compared with previous studies.

Minimum pickup velocity (U pu) of nanoparticles in gas–solid pneumatic conveying

This paper is the first systematic study of the pneumatic conveying of nanoparticles. The minimum pickup velocity, Upu, of six nanoparticle species of different materials [i.e., silicon dioxide (SiO2), aluminum oxide (Al2O3), and titanium dioxide (TiO2)] and surfaces (i.e., apolar and polar) was determined by the weight loss method. Results show that (1) due to relative lack of hydrogen bonding, apolar nanoparticles had higher mass loss values at the same velocities, mass loss curves with accentuated S-shaped profiles, and lower Upu values, (2) among the three species, SiO2, which has the lowest Hamaker coefficient, exhibited the greatest discrepancy between apolar and polar surfaces with respect to both mass loss curves and Upu values, (3) Umf,polar/Umf,apolar was between 1 and 3.5 times that of Upu,polar/Upu,apolar due to greater extents of hydrogen bonding associated with Umf, (4) Upu values were at least an order-of-magnitude lower than that expected from the well-acknowledged Upu correlation (Kalman et al., Powder Technol 160:103–113, 2005) due to agglomeration, (5) although nanoparticles should be categorized as Zone III (Kalman et al. 2005) (or Geldart group C, Powder Technol 7:285–292, 1973), the nanoparticles, and primary and complex agglomerates agreed more with the Zone I (or Geldart group B) correlation.

Incompressible SPH scour model for movable bed dam break flows

In this study an incompressible smoothed particle hydrodynamics (ISPH) approach coupled with the sediment erosion model is developed to investigate the sediment bed scour and grain movement under the dam break flows. Two-phase formulations are used in the ISPH numerical algorithms to examine the free surface and bed evolution profiles, in which the entrained sediments are treated as a different fluid component as compared with the water. The sediment bed erosion model is based on the concept of pick-up flow velocity and the sediment is initiated when the local flow velocity exceeds a critical value. The proposed model is used to reproduce the sediment erosion and follow-on entrainment process under an instantaneous dam break flow and the results are compared with those from the weakly compressible moving particle semi-implicit (WCMPS) method as well as the experimental data. It has been demonstrated that the two-phase ISPH model performed well with the experimental data. The study shows that the ISPH modelling approach can accurately predict the dynamic sediment scouring process without the need to use empirical sediment transport formulas.

Impact of continuous particle size distribution width and particle sphericity on minimum pickup velocity in gas–solid pneumatic conveying

The minimum pickup velocity (Upu) for pneumatic conveying is analogous to the minimum fluidization velocity (Umf) in fluidization systems in that both dictate the minimum gas velocity required and have important implications in gas–solid flows. However, Upu is not as well-understood as Umf. In this work, the impact of the width of lognormal particle size distributions (PSDs) and particle sphericity (φ) on Upu was determined by the modified weight loss method. Three Geldart Group B materials (namely, glass, aluminum oxide and plastic), with various PSD widths and different particle sphericities (φ), were investigated. Two observations are worth highlighting: (i) as PSD width increases, Upu surprisingly exhibits a non-monotonic behavior (namely, decreases then increases), and (ii) the lower the particle sphericity (φ) is, the greater the extent of the non-monotonic behavior becomes. The discrepancy between the Upu values of the experimental data here and values predicted by available correlations underscores the non-negligible impact of PSD width and particle sphericity, which thereby warrants more understanding and the incorporation of such effects to improve the predictive capability of gas–solid pneumatic conveying.

Constraints on the functional form of the critical deposition velocity in solid–liquid pipe flow at low solid volume fractions

Of the various transition velocities that delineate flow regimes in multiphase pneumatic and hydraulic conveying, the critical deposition velocity is important because it separates depositing and non-depositing flows. However, no distinction has been made between the dependence of the critical deposition velocity on physical parameters and flow conditions at low solid volume fractions and in the limit of zero volume fraction, which are distinct mathematically. Here, the two cases are analysed separately, and a general functional form in terms of the particle Reynolds number and Archimedes number is proposed that is valid up to volume fractions of several per cent. An ultrasonic method for determining the critical value of the particle Reynolds number is presented, and results for four particle types at several nominal volume fractions (0.5, 1 and 3% by volume) are combined with a number of data from the literature. The resulting expressions are found to compare well with several similar correlations for the critical deposition velocity and other transition velocities, and, unlike a recent best-fit approach for the pick-up velocity, incorporate an explicit dependence on volume fraction, to which the critical deposition velocity is most sensitive at very low volume fractions. Lastly, it is found that the functional forms for the critical deposition velocity in the literature are unable to reproduce the available data at higher volume fractions, and a number of suggestions are made for resolving this issue.

On the prediction of pickup and saltation velocities in pneumatic conveying

This paper presents a comparative study of the critical pickup and saltation velocities of particles in horizontal pipelines for pneumatic conveying design. A comparative study is performed using different existing correlations in the literature for the determination of the minimum velocity of transport as a function of the particle and pipe diameter, particle density, solid mass flow rate and particle sphericity. Their limitations and difficulties in predicting those critical velocities are analyzed. For the pickup velocity, an experimental study was also carried out in order to support the analysis. Recommendations are presented on the use of such correlations.

Effect of particle size and sphericity on the pickup velocity in horizontal pneumatic conveying

This paper presents a theoretical and experimental analysis of the influence of particle size and sphericity on the pickup velocity in horizontal pneumatic conveying. An analytical model was developed to predict the pickup velocity based on force and moment balances taking particle size and sphericity into account. In this work it was demonstrated analytically that the pickup velocity of a particle increases when particle sphericity decreases. An experimental apparatus was developed in order to verify the influence of the diameter particle and pipeline on pickup velocity, and to validate the proposed analytical model. The obtained equations to the pickup velocity prediction cover a particle diameter range of 20–4000μm, densities range 1000–5000kg/m3 and pipeline diameter ranging from 25 to 150mm in the prediction of the minimum gas velocity required to pickup particles. These results agree with the experimental data available from the literature.

Electromagnetic ion cyclotron wave generation by planetary pickup ions: One‐dimensional hybrid simulations at sub‐Alfvénic pickup velocities

Enhanced electromagnetic plasma waves generated by unstable pickup ion distributions have been detected by spacecraft in several planetary environments including those of Venus, Earth, Mars, comets, Jupiter and Saturn. These waves are important because they can be used as a diagnostic of the local plasma and the ion pickup conditions. Interpretation of these waves relies on understanding the source of free energy and how that free energy is reduced through instability growth. In this manuscript, we focus on the regime where the pickup velocity is sub‐Alfvénic and systematically illustrate some basic differences in instability behavior by carrying out one‐dimensional hybrid simulations of pickup ion‐generated waves for varying pickup angle, α. Although several pickup ion‐driven instabilities are possible in this regime, the dominant electromagnetic instability that is observed is the ion cyclotron ring instability, which generates waves in the spacecraft frame with frequencies near the pickup ion cyclotron frequency. To better understand the instability behavior as well as what wave properties a spacecraft would potentially observe, we carry out the simulations in the bulk plasma frame and in the planetary rest frame (i.e. spacecraft frame). The simulations presented here are not meant to reproduce any particular planetary environment but are intended to illustrate the general behavior in the sub‐Alfvénic pickup velocity regime. We also review the previous observations and dispersion analyses of pickup ion‐driven waves in the relevant planetary environments, and discuss them in terms of our simulation results.