Impactor Performance Research Articles

Study on the Influence of Fluid Pulsation on Hydraulic Impactor Performance in Drilling Engineering

The combination of the hydraulic impactor and positive displacement motor (PDM) is becoming more and more popular in drilling engineering. However, the negatives of the PDM on the impactor cannot be ignored. To improve the performance of the technique, the influence of fluid pulsation from the PDM on the hydraulic impactor was studied first; then, the structure of the impactor was optimized to improve its impact force; finally, field tests were carried out in 2 wells in the shallow formation. The results indicate that the fluid fluctuation generated in the PDM can restrain the performance of the impactor, and that the impact force can be increased by 24.4% to 28.6% through the optimization of design. Field tests show that this technique can further improve the drilling efficiency and rotating stability of the polycrystalline diamond compact bit, and that the rate of penetration and bit footage increase by 32.5% and 34.6%, respectively. In the study, the effect of inlet fluid fluctuation on the performance of the hydraulic impactor was studied using the computational fluid dynamics method. This is unlike other studies that have mostly considered the inlet fluid as a steady flow. Furthermore, the performance of the combine used of the impactor and PDM can be improved through structural optimization.

Virtual impaction in compressible flows with pressure recovery

Virtual impactors have been utilized towards classifying and increasing aerosol concentrations in sampling and measurement systems for half a century; in an ideal virtual impactor, sampled particles larger than a critical diameter (known as the cutsize) are directed inertially into a small fraction of the sample flow, known as the minor flow. Concentrating submicrometer particles with virtual impactors while maintaining near-atmospheric pressure downstream in the minor flow remains a challenge, due the low mass-to-drag ratios of these particles. Increased inertial behavior for small mass-to-drag ratio particles can be overcome by increasing flow velocities; however, in most prior work with virtual impaction of submicrometer particles, pressure recovery (keeping the aerosol outlet pressure similar to the inlet pressure) in the receiving tube at high sample flow rates was not investigated. Here, we describe the development and testing of virtual impactors functioning with flow velocities near the sonic limit, capable of submicrometer particle concentration, and with near-complete pressure recovery in the minor flow. We specifically designed, built, and tested two round-nozzle virtual impactors (denoted as VI-1 and VI-2) and evaluated their performances using fluorescent polystyrene latex particles and uranine-doped oleic acid particles with varying particle diameter. The results show that both virtual impactors, operating with 12 L per minute sample flow and a 10:1 sample flow-to-minor flow ratio, have submicrometer cutsizes (∼700 nm and 200 nm for VI-1 and VI-2, respectively) and near-complete pressure recovery. However, significant particle losses were observed in VI-2 with larger particle diameters. To understand such losses and particle trajectories in compressible flow virtual impactors, we also carried out computational fluid dynamics (CFD) simulations coupled with particle trajectory simulations. Importantly, trajectory calculations incorporated a recently developed drag model capable of predicting particle drag coefficients in a wide Mach number and Knudsen number (and hence Reynolds number) range. Trajectory calculations yielded cutsizes and large particle penetration curves in good agreement with experiments, indicating that large particle losses are due to overfocusing (radial inertial motion leading to deposition) within the nozzle and major flow chamber. Overfocusing always leads to an upper size limit in any virtual impactor system, but it is of greater concern in higher velocity systems. In addition to comparing simulations to measurements sampling at atmospheric pressure, we used trajectory calculations to examine compressible flow virtual impactor performance with variable sampling flow pressure and varying the driving pressure in the major flow. Such simulations reveal that sub-atmospheric pressure sampling leads to a reduced penetration “window” for virtual impaction, such that although it is possible for virtual impactor operation in reduced pressure environments, virtual impactors are applicable to a decreasing range of sizes at low pressure.

Challenge with a Personal Cascade Impactor Sampler in a Silicon Metal Smelter

ABSTRACT Cascade impactors are useful tools in the measurement of particle size mass distribution of workplace aerosols. The application of cascade impactors, however, is sometimes challenging. Personal aerosol samples were collected by Sioutas cascade impactors and respirable cyclones in parallel in a silicon (Si) metal smelter to investigate the different particulate matter (PM) fractions. In a second campaign, nine new air samples were collected with the Sioutas personal cascade impactors using stationary sampling. It was found that wall deposition was substantial in the upper stages of the Sioutas cascade impactors, which meant that quite often more PM was deposited on the inner walls of the impactor than on the filter substrates. At the same time, wall deposition did most probably not affect the collection of the finest particles (< 0.25 µm). Besides wall deposition of the particles, the effect of high PM concentration on the impactor performance, particle bouncing and blow off, high particle mass loading and impact fragmentation of the particle agglomerates were considered for explaining the malfunctioning of the Sioutas impactors in the Si metal smelter. Furthermore, concentrations of the finest PM fraction (< 0.25 µm) and respirable fraction both collected by personal sampling are reported and discussed in the paper.

Cascade Impactor Performance of Commercial pMDI Formulations Using Modified Induction Ports.

The induction port (IP) for aerosol analysis with the Next Generation Pharmaceutical Impactor as monographed in the United States and European pharmacopoeia (USPIP) lacks physiological relevance, which, amongst other reasons, has been identified as critical for the predictability of in vitro aerosol data to lung deposition observed in vivo. In this publication, we report the impact of replacing the USPIP with two modified induction ports, which were designed based around geometries derived from a computer tomographic scan of a human trachea and the distal section of the USPIP. Test formulations were selected on the basis of availability of in vivo lung deposition data so that results obtained in vitro could be evaluated for their predictability. All formulations assessed showed increased deposition in the modified induction ports, and different mechanisms of particle deposition have been identified. In vitro predictions of the lung deposition were found to correlate well with the in vivo observations reported using the modified induction ports. Furthermore, the quality of the correlation was found superior to the one achieved with the USPIP with an average deviation of the predicted from observed values (n = 10) of 6 ± 4, 12 ± 6, and 16 ± 6% for the modified induction ports (mIP and mIPext) and the USPIP, respectively, when using a fine particle fraction (FPF) cutoff value of 5 μm. Using a FPF cutoff value of 3 μm yielded a more accurate in vitro-in vivo correlation with an average deviation of the predicted from observed values of 5 ± 4, 7 ± 5, and 8 ± 4% for the mIP, mIPext, and USPIP, respectively. For both FPF size cutoff values, the mIP yielded the most accurate in vitro-in vivo correlation.

Influence of the Dilution System and Electrical Low Pressure Impactor Performance on Particulate Emission Measurements from a Medium-scale Biomass Boiler

ABSTRACT The accurate monitoring of particulate emissions from medium-scale, decentralized biomass combustion units is a major challenge for the deployment of this technology in the frame of the current energy transition. More specifically, the experimental characterization of the size of the emitted particles, i.e. using impactors, is still subject to discussions about the impact of the methodology on the measurement results. To meet with these challenges, particulate emissions from a medium-scale biomass boiler (4.5 MWth) were measured with Electrical Low Pressure Impactors (ELPI+) using two different dilution systems to examine the effect of dilution and performance of the ELPI+. For both the two stage dilution systems and one stage dilution system, no statistically significant correlation was found between the dilution ratio (DR) and particle total number concentration Ntot or between DR and mass concentration mtot. However, with both dilution system, a significant positive correlation was observed between DR and particles with diameter Dp < 0.01 µm due to measurement artefacts. With the one stage dilution system dilution systems, condensation appears to be promoted with reduced DR. When the ELPI+ impactor is not overloaded, the number concentration of fractions N< 0.01 and N0.01-0.1 reduce over time due to prematurely measuring particles. When the impactor is overloaded, N< 0.01 is overestimated and N0.01-0.1 and N0.1-1 are underestimated due to a change in cut-off diameter.

Investigating cascade impactor performance using a modified 3D printed induction port

Based on a computer tomographic scan of a human trachea, a modified induction port (mIP), for use with the Next Generation Cascade Impactor, was manufactured using 3D printing technology. Standard United States Pharmacopoeia IP (USPIP) was compared to the mIP and a 3D printed version of the USPIP (USP3DIP) by analyzing different types of commercial salbutamol formulations for inhalation. Increased retention of particles in the mIP was found analyzing a pMDI formulation, leading to a decrease in the FPF from 28.8±2.0% to 14.2±1.2%, which correlates better to in vivo deposition data from literature. Increased deposition was found to be based on geometrical factors only. The impact of surface related effects was investigated by (a) comparing results obtained with the USPIP and USP3DIP (all formulations) and (b) generating another model IP (USP3DSEIP) with a surface area equivalent to the mIP but maintaining the geometry of the USPIP (pMDI only). USPIP, USP3DIP, and USP3DSEIP were found to perform equivalently. The impact of different geometries on airflow velocities in the USPIP and mIP was assessed using a computational fluid dynamics (CFD) model. Conclusively, this study shows that replacing the USP IP by the mIP can provide additional information in formulation assessment and in in vitro/in vivo correlation, when applied on pMDI formulations.

Effect of convergence angle on impactor performance

ABSTRACTTwo nozzles, modified and original, were tested in a sampler that was placed in a wind tunnel and penetration efficiencies, √Stk50, and slope of the performance curve were determined by challenging the sampler with fluorescent-tagged monodisperse test aerosol particles having known concentration. It was shown that a change in convergence angle of the modified nozzle can affect impactor performance. The √Stk50 for original and modified nozzles were 0.57 and 0.49, respectively. The slope of the efficiency curve for original and modified nozzles was 1.52 and 1.36, respectively.© 2017 American Association for Aerosol Research

Computational fluid dynamics (CFD) investigation of the gas–solid flow and performance of Andersen cascade impactor

The Andersen cascade impactor (ACI) is a device designed to fractionate aerosols by their aerodynamic diameters. This work developed a computational fluid dynamics (CFD) model to investigate flow characteristics and particle deposition behaviour in an ACI. A novel Iterative Simulation (IS) modelling technique was adopted to map the flow information between the source and target zones of individual models, hence enabling the establishment of flow fields across the whole device as a single domain. Particle trajectories and deposition were evaluated using the Lagrangian tracking approach in conjunction with the application of a kinetic energy criterion (KEc). The model was validated by comparing the simulation results with literature and manufacturer's data. The effect of flow rate was evaluated by using the standard and high flow rates of 28.3 and 60Lmin−1. The results showed that operating the ACI at high flow rates reduced the impactor performance by magnifying the cross-flow interactions and recirculation vortices. The heavy wall losses observed at Stages 2 and 3 of the impactor were attributed to more pronounced recirculation vortices at these stages. Increasing particle deposits underneath Stages 0 and 1 around the central ring of jet outlets can be attributed to counter-current flows arising from the central holes in the plates. These conclusions have significant implications for the design and operation of the ACI.

Dynamic Performance Analysis of Gas-Liquid United Hydraulic Hammer

In order to improve the impactor performance, the dynamic performance of gas-liquid united hydraulic hammer should be optimized. Based on the analysis of the operating principle for the hydraulic impactor, one simulation model of gas-liquid united hydraulic impactor was built with AMESim software. By setting different simulation parameters, curves of displacement, velocity, acceleration and cavity pressure were obtained under different working conditions. The key component can be obtained by the analysis of activity index. The whole simulation results provide a reliable basis for component selection and parameter optimization of hydraulic impactor.

CFD simulations of the Andersen cascade impactor: Model development and effects of aerosol charge

Cascade impactors are commonly used to assess the size characteristics of aerosols in toxicology and pharmaceutical applications. These aerosol instruments have been developed and refined over decades. However, a number of questions remain related to impactor performance, including the influence of electrostatic charge on measured size distributions. The objective of this study was to develop a validated CFD model of the Mark II Andersen cascade impactor (ACI) and apply this model to evaluate the effects of particle charge on deposition. The flow field was simulated using a commercial CFD code for incompressible laminar and transitional flows. Particle trajectories and deposition were evaluated using a well tested Lagrangian tracking approach that accounts for impaction, sedimentation, diffusion, and electrostatic attraction. Particle charge levels typical of dry powder inhaler (DPI) and metered dose inhaler (MDI) aerosols were considered for a particle size range of 0.3–12 μm. As a model validation, computational predictions of cutoff d 50 diameters for each of the eight ACI stages were found to be within 10% difference of existing experimental and manufacturer data. Results indicated that charges consistent with DPI and MDI aerosols increased deposition fraction in Stages 0–3 by up to 30% and increased deposition fraction in Stages 4–7 by up to an order of magnitude. For Stages 0–3, both DPI and MDI charges reduced the d 50 value by approximately 10% or less. In contrast, charged aerosols reduced the d 50 values in Stages 4 and 5 by 200% and 60%, respectively. All charged submicrometer aerosols considered deposited in Stages 6 and 7. Increasing the particle charge by an order of magnitude from DPI to MDI values had a relatively small effect on further decreasing the cutoff size of each stage. In conclusion, these results can be used to approximate the actual aerodynamic diameter of a charged pharmaceutical aerosol based on measurements in a standard ACI. Future applications of the developed ACI model include evaluating the influence of space charge on deposition and quantifying the effects of aerosol condensation and evaporation on size assessment.

Numerical calibration of the Andersen cascade impactor using a single jet model

A single jet model is described and used to analyze the performance of an 8-stage Andersen cascade impactor (ACI). The two-dimensional axisymmetric jet flow field was calculated numerically by solving the Navier–Stokes equations and particle trajectories were then analyzed to obtain the collection efficiency curves at different flow rates. The resulting efficiency curves and corresponding cutoff diameters were compared and found to be in good agreement with the available experimental data. We also examined the effect of gravity on impactor performance and discuss the limitations of the single jet model.

Computational fluid dynamics simulation of virtual impactor performance: Comparison to experiment

Computational fluid dynamics (CFD) simulations were performed on a slit virtual impactor (SVI). A full-section planar model of the critical zone (nozzle) was constructed based on the measured values of geometrical dimensions of the SVI. Simulation was performed for a flow rate of 20.33 SCFH (standard cubic feet per hour) that corresponded to a Reynolds number value of 448 in the experiment. Impactor efficiency curve was computed and compared to experimental data. Details of internal wall losses were characterized and the wall loss curve was generated. Performance characteristics obtained from simulation results are in good agreement to the observed experimental trend over the complete range of Stokes numbers and the exact value of the cut-point Stokes number. Tracks for lower Stokes number particles faithfully reproduce the trend observed in the experiment, namely the regional demarcation of particle origin in the inlet nozzle, based on their final destination. Further, the effect of crossing trajectories that was visualized in the experiment for higher Stokes number particles of value of ~ 50 was captured. Additional details from the simulation results indicated that the onset of effect of crossing trajectories occurred for particles larger than a Stokes number of 6 and the collection efficiency for the above device was nearly unity over a wide range of Stokes number (Stk ~ 2 to 125) values.

CFD Study on the Effects of the Large Particle Crossing Trajectory Phenomenon on Virtual Impactor Performance

Two-dimensional CFD simulations were performed on a full-section numerical model of an as-built slot virtual impactor prototype and its completely symmetric ideal counterpart. The simulations reproduce the trends of the experimentally observed performance including verification of a third region in the transmission efficiency curve, which is a drop-in transmission efficiency for large particle sizes. Visualization of simulated particle tracks show this decrease is attributed to a crossing trajectory phenomenon, whereby larger particles that acquire enough inertia in a chamfered acceleration nozzle, crossover the vertical mid-plane and impact on the opposite-side wall, particularly on the wall of the receiver section. Some experimental data presented in the literature for rectangular slot and round-nozzle virtual impactors with chamfered 45° half-angle acceleration nozzles (similar to the geometry tested herein), show a similar drop-in transmission efficiency that commences at a particle Stokes numbers of ...

Influence of Impactor Operating Flow Rate on Particle Size Distribution of Four Jet Nebulizers

When a nebulizer is evaluated by the Andersen Cascade Impactor (ACI), the flow rate is generally maintained at 28.3 L/min, as recommended by the manufacturer. However, the nebulizer flow rate that a patient inhales is only around 18 L/min. Because the drive flow of a nebulizer is approximately 6–8 L/min, the nebulized drug is mixed with outside air when delivered. Evaluating impactor performance at the 28.3 L/min flow rate is less than ideal because an additional 10 L/min of outside air is mixed with the drug, thereby affecting the drug size distribution and dose before inhalation and deposition in the human lung. In this study we operated the ACI at an 18.0 L/min flow rate to test whether the effect of the changing ambient humidity was being exaggerated by the 28.3 L/min flow rate. The study was carried out at three different relative humidity levels and two different impactor flow rates with four commercially available nebulizers. The mass median aerodynamic diameter (MMAD) and the geometric standard deviation (GSD) of the droplets were found to increase when the impactor was operated at a flow rate of 18 L/min compared to that of 28.3 L/min. The higher MMAD and GSD could cause the patient to inhale less of the drug than expected if the nebulizer was evaluated by the ACI at the operating flow rate of 28.3 L/min.

Design of a Slot Nanoparticle Virtual Impactor

A novel design for a nanoparticle slot virtual impactor is proposed. Compressible flow through the slot impactor is simulated using the CFD code FLUENT, and the corresponding particle trajectories are studied. The variation of the impactor performance with design parameters is also investigated. The design is optimized for a specific application where the virtual impactor serves as a preconcentrator. However, the design proposed is suitable for any application that requires concentration of ultrafine particles at high volumes. Additionally, the design developed in this work can be used for size selection by simply varying the operating pressure of the instrument. The 50% cut-off diameter varies from 13 nm to 200 nm as the operating pressure is increased by a factor of 20, without affecting the minor to total flow ratio significantly.

Optimization Studies on a Slit Virtual Impactor

This study reports the results of numerical investigations performed on a proposed slit virtual impactor configuration. Simulations were performed using the computational fluid dynamics program CFX-4.4. A detailed numerical investigation was carried out to determine the critical geometrical parameters of the proposed configuration that would optimize the performance for the anticipated operation conditions (specified Reynolds number and major-to-minor flow split ratio). A detailed sensitivity analysis was performed on the optimized configuration to determine its performance characteristics (impactor efficiency and wall loss curves) for (a) operation at different major-to-minor flow split ratios for a constant Reynolds number and (b) operation at different Reynolds numbers but at the same major-to-minor flow split ratio. Finally, the effect of modifying the radius of curvature of the receiving section of the optimized configuration on the impactor performance was studied for the anticipated operation conditions, and the results are reported.

Computational fluid dynamics simulation of a rectangular slit real impactor's performance

The performance of a rectangular slit impactor was simulated using the three-dimensional computational fluid dynamics (CFDs) computer program CFX-4.4. The characteristic impactor efficiency curve obtained from the simulations was compared with the experimental results. A sensitivity study was carried out to investigate the effect of (a) the total number of particles used for the simulation, (b) gravity in the simulation, and (c) ultra-Stokesian drag on the efficiency curve predictions. The simulation predictions for each of the above cases are presented along with the experimental data and the results are discussed. Results obtained from the simulation are seen to be in good agreement with experimental data, validating the particle transport model implemented in CFX-4.4, for laminar flow conditions.

Simultaneous Use of Polystyrene Latex Particles of Different Sizes to Evaluate Performance of a Cyclone and Impactor

Monodisperse and polydisperse aerosols were produced to evaluate the effect of particle size on cyclone and impactor performance. Monodisperse aerosols were generated from polystyrene latex and divinylbenzene particles. Polystyrene aerosols were also generated by mixing several monodisperse aerosols of different sizes. The mixture ratio of monodisperse aerosols was found by trial and error to generate polydisperse aerosols. Generated polydisperse aerosols had multimodal aerosol size distribution, which had the same peak point as shown in the size distribution of monodisperse particles. The results show the collection efficiency curves of a cyclone and impactor, when generating monodisperse particles were coherent with those for polydisperse ones. Our findings show that the size distribution and the size range of test aerosols can be easily determined by mixing monodisperse particles of known particle sizes, using a time saving procedure.

Determination of large aerosol particle size by elutriation.

Inhalable dust fraction determination requires aerodynamic size information for large aerosol particles. Operation of cascade impactors at flows that collect these particles leads to jet Reynolds numbers outside the range of established impactor performance. Horizontal elutriators, designed to match earlier respirable dust curves at a single flow rate, may be used to provide aerodynamic size information for particles larger than 50 microm. Operation of these elutriators at higher than design flow rates and angles other than horizontal provides for particle penetration over the size range of the inhalable dust curve. Equations are provided that relate penetration, flow rate, and angle to aerodynamic diameter to allow for bracketing the desired size and distribution. The use of impactor data reduction methods to determine size distributions with the MRE horizontal elutriator is examined with a spreadsheet model. Comparison of elutriator size determination with an impactor in the 10 to 15 microm range, where both methods could be used, resulted in reasonable agreement. This method provides for determination of aerodynamic characteristics of large aerosols in field sampling conditions.

The effect of varying impaction plate temperature on impactor performance: experimental studies

This study concerns the effect of impaction plate temperature change on impactor performance. The impaction plate was cooled or heated with a thermoelectric module, and the temperature of the impaction plate was monitored by the thermocouple. The size of used particles ranged from 1 to 10 μm . Finally, a collection efficiency curve was obtained by employing a TSI Aerosizer. The results reveal that cooling the impaction plate makes the impactor collection efficiency higher and the re-entrainment lower. Therefore, cooling gives a more desirable collection efficiency curve. The increased adhesion effect on the impaction plate explains this. Based on the present investigations, cooling the impaction plate enhances impactor performance without using coating materials. A new type of impactor with a thermoelectrically cooled plate is demonstrated to be useful in this experimental study.