Synthesis and characterization of silicalite-1 membrane prepared on a novel support by the pore plugging method

The effect of the support pore size on the membrane morphology was investigated for zeolite silicalite-1 membranes synthesized by pore plugging method on supports with zirconium oxide and/or titanium oxide active layer. Parameters including surface coverage, zeolite layer thickness, crystal size and shape, zeolite penetration depth were used to quantify the membrane morphology. Five supports with different pore sizes for their active layer in the range of 0.14–1.4 μm were investigated. The X-ray diffraction (XRD) analysis showed a typical silicalite-1 zeolite structure with a high internal crystalline order grown inside the pores as well as on top of all supports. The XRD results also showed that the silicalite-1 crystals in the synthesized membranes are not randomly oriented. The crystallographic preferred orientation (CPO) analysis revealed that the degree of orientation toward either the a-axis or b-axis perpendicular to the support surface, increased by decreasing the pore size of the support. The 0.45 μm support had the most preferably oriented zeolite layer for access of molecules entering into the membrane structure with the highest number of crystals oriented with the b-axis (the one with straight channels) perpendicular to the support surface. The scanning electron micrographs (SEM) analysis of the membranes revealed a dense and continuous surface morphology with the highest crystal size of silicalite-1 around 1.5 μm on the surface of the support with the 0.45 μm pore size. SEM micrographs also showed a continuous layer grown over four supports out of five supports with different pore sizes that were investigated, with no layer observed on the 1.4 μm pore size support. The average thickness of the zeolite layer was in the range of 0.7–1.4 μm, depending on the pore size of the support. The supports with 0.2 and 0.45 μm pore sizes had the most uniform zeolite layer thickness while the support with 0.8 μm pore size active layer had the least uniform zeolite layer thickness. The electron diffraction spectrometer (EDS) analysis confirmed the formation of pure silicalite-1 layer at the surface as well as inside the pores of all supports. The highest silicalite-1 crystal penetration was for the supports with 0.45 and 1.4 μm pore sizes. Single gas permeation experiments with He and N₂ gases at 293 K illustrated that regardless of the pore size of the support, the He and N₂ permeances were constant despite the change of the pressure across the membranes. The highest permeances were observed for the membrane prepared using the 0.45 μm pore size support, while the lowest permeances were for the membrane prepared using the 1.4 μm pore size support. These results confirmed the selective properties of the prepared membranes. No matter what is the pore size of the support or the feed pressure, N₂ permeances were around three times higher than those for He.     

Surface-collection efficiency of Nuclepore filters for nanoparticles

The flat surface of Nuclepore filters is suitable for observing collected particles with a scanning electron microscope (SEM). However, experimental data on surface-collection efficiency are limited because surface-collection efficiencies cannot be measured directly using aerosol measuring instruments. In this study, the surface-collection efficiencies of Nuclepore filters were determined by establishing the ratio of the number of particles deposited on the surface of the filter visually counted with an SEM to the number of inflow particles counted by a condensation particle counter, using monodispersed polystyrene latex particles (30–800 nm) and silver particles (15–30 nm). Because Nuclepore filters with smaller pore sizes would be expected to produce higher minimum surface-collection efficiency and a higher pressure-drop, 0.08 and 0.2 µm Nuclepore filters were chosen as the test filters in view of both collection efficiency and pressure drop. The results showed that the minimum surface-collection efficiencies of the 0.08 µm pores at face velocities of 1.9 and 8.4 cm·s^?1 were approximately 0.6 and 0.7, respectively, and those of the 0.2 µm pores at face velocities of 1.5 and 8.6 cm·s^?1 were approximately 0.8 and 0.6, respectively. Because the pressure drop of the 0.2 µm pore filter was lower than that of the 0.08 µm pore filter under the same flow-rate conditions, the 0.2 µm pore filter would be more suitable considering the pressure drop and collection efficiency. The obtained surface collection efficiencies were quantitatively inconsistent with theoretical surface-collection efficiencies calculated using conventional theoretical models developed to determine the collection efficiency of filters with larger pores.

© 2016 American Association for Aerosol Research     

Nanoparticle collection efficiency of capillary pore membrane filters

The surface and overall collection efficiencies of capillary pore membrane filters were measured for sub-micrometer particles. Collection efficiencies were derived from the surface loadings of particles on filters measured by scanning electron microscopy and from airborne particle concentrations measured with a scanning mobility particle sizer. Tests used filters with nominal pore diameters of 0.4 and 0.8 μm and face velocities of 3.7 and 18.4 cm/s. Surface collection efficiencies were below 100% for particles smaller than 316 nm and below 55% for particles smaller than 100 nm. Overall collection efficiencies reached as low as 45% for 70 nm particles. For nanoparticles, collection efficiencies overall were substantially higher than those to the filter surface, indicating that deposition occurs to a large extent inside the filter pores. These results underscore the need to account for surface collection efficiency when deriving airborne concentrations from microscopic analysis of nanoparticles on capillary pore membrane filters.     

Novel Instrument to Separate Large Inhalable Particles

Large inhalable particles are present in the workplace, yet few instruments exist to count and size such particles in situ. Inhalable-aerosol exposure can be evaluated using mass-based samplers such as the IOM or Button sampler, but these devices do not provide information on particle size distributions. Size-resolved samplers such as cascade impactors or the Aerodynamic Particle Sizer are limited to particle sizes <20 μm due to difficulties with particle aspiration and transmission losses. This work describes the development of two samplers capable of measuring the concentration and size distribution of airborne particles from 20 to 100 μm in aerodynamic diameter. One device is based on the principles of an upflow elutriator, whereas the other eliminates the potentially adverse effects of an upward-facing jet to separate particles from a quiescent airstream. Analytical models and computational fluid dynamics simulations were used to predict the performance of the two samplers. Sampling efficiencies of these devices were tested in a calm-air chamber with polydisperse, fluorescent microspheres (10–100 μm). Epifluorescent microscopy of settled dust was used to determine reference particle counts and sizes. Both devices are capable of size-selective sampling; however, the second sampler produced higher sampling efficiencies and sharper cut points compared to the simpler elutriator design. Experimental sampling efficiencies for both samplers showed good agreement with computational and analytical solutions. This work suggests that these devices can size-segregate inhalable aerosols in quiescent environments.

Copyright © 2015 American Association for Aerosol Research     

High-Volume Aerosol Filtration and Mitigation of Inertial Particle Rebound

The performance of electrostatically charged blown microfiber filter media was characterized for high-volume sampling applications. Pressure drop and aerosol collection efficiency were measured at air pressures of 55.2 and 88.7 kilopascals (kPa) and filter face velocities ranging from 2.5 to 11.25 meters per second (m/s). Particle penetration was significant for particles above 0.5 micrometers (μm) in aerodynamic diameter where the onset of particle rebound was observed as low as 200 nanometers (nm). Particle retention was enhanced by treating filters in an aqueous solution of glycerol. Adding this retention agent eliminated electrostatic capture mechanisms but mitigated inertial rebound. Untreated filters had higher nanoparticle collection efficiencies at lower filter face velocities where electrostatic capture was still significant. At higher filter face velocities, nanoparticle collection efficiencies were higher for treated filters where inertial capture was dominant and particle rebound was mitigated. Significant improvements to microparticle collection efficiency were observed for treated filters at all air flow conditions. At high air pressure, filter efficiency was greater than 95% for particles less than 5 μm. At low air pressure, performance enhancements were not as significant since air velocities were significantly higher through the fiber mat. Measured single fiber efficiencies were normalized by the theoretical single fiber efficiency to calculate adhesion probability. The small fiber diameter (1.77 μm) of this particular filter gave large Stokes numbers and interception parameters forcing the single fiber efficiency to its maximum theoretical value. The adhesion probability was plotted as a function of the ratio of Stokes and interception parameter similar to the works of others. Single fiber efficiencies for inertial nanoparticle collection were compared to existing theories and correlations.

Copyright 2014 American Association for Aerosol Research     

Prediction of Dimensionless Cutsize for Size‐Fractionated Measurements of Particles that Impact on a Sintered Stainless‐Steel Filter

Abstract

This investigation experimentally studied the penetration curve of particles that impact on a sintered stainless‐steel filter with various pore sizes, sampling flow rates and jet diameters. The penetration curves were compared to those with an aluminum foil substrate. Test data reveal that when the sintered stainless‐steel filter has larger pore sizes (100 µm or 40 µm), the particle penetration, P(%), is lower and the curve is less steep than that obtained from the aluminum foil substrate. The penetration curve of the sintered stainless‐steel filter with smaller pore size (5 µm) is close to that of the aluminum foil substrate. The dimensionless cutsize‐shift (the ratio of the dimensionless cutsize of sintered stainless‐steel filter to that of aluminum foil) falls as the pore sizes and the Reynolds number increase. Experimental data were then compared with theoretical results, and theory over‐predicted the dimensionless cutsize‐shift. Hence, a regression equation for the dimensionless cutsize‐shift is proposed by fitting the experimental data. The discrepancy between the experimental data and the regression prediction is within 4%. The regression equation can be used to predict the dimensionless cutsize for the size‐fractionated measurements of particles that impact on a sintered stainless‐steel filter with various sized pores and Reynolds numbers.     

Aerosol Generation by Modern Flush Toilets

A microbe-contaminated toilet will produce bioaerosols when flushed. We assessed toilet plume aerosol from high efficiency (HET), pressure-assisted high efficiency (PAT), and flushometer (FOM) toilets with similar bowl water and flush volumes. Total and droplet nuclei “bioaerosols” were assessed. Monodisperse 0.25–1.9-μm fluorescent microspheres served as microbe surrogates in separate trials in a mockup 5 m³ water closet (WC). Bowl water seeding was approximately 10¹² particles/mL. Droplet nuclei were sampled onto 0.2-μm pore size mixed cellulose ester filters beginning 15 min after the flush using open-face cassettes mounted on the WC walls. Pre- and postflush bowl water concentrations were measured. Filter particle counts were analyzed via fluorescent microscopy. Bowl headspace droplet count size distributions were bimodal and similar for all toilet types and flush conditions, with 95% of droplets <2 μm diameter and >99% <5 μm. Up to 145,000 droplets were produced per flush, with the high-energy flushometer producing over three times as many as the lower energy PAT and over 12 times as many as the lowest energy HET despite similar flush volumes. The mean numbers of fluorescent droplet nuclei particles aerosolized and remaining airborne also increased with flush energy. Fluorescent droplet nuclei per flush decreased with increasing particle size. These findings suggest two concurrent aerosolization mechanisms—splashing for large droplets and bubble bursting for the fine droplets that form droplet nuclei.

Copyright 2013 American Association for Aerosol Research     

A Cylindrical Thermal Precipitator with a Particle Size-Selective Inlet

We designed a thermal precipitator in a cylindrical configuration with a size-selective inlet, and investigated its performance in experiments using differential mobility analyzer (DMA)-classified particles of sodium chloride (NaCl) and polystyrene latex (PSL). Our investigation was performed in two parts: (1) using the size-selective inlet to determine the best inlet-to-wall distance for optimal impaction of 1 μm particles; (2) using a simple inlet tube to measure particle collection via thermophoresis over a size range from 40 nm to 1000 nm. The results showed that the inlet had a particle cut-off curve, with a 50% particle cut-off Stokes number of 0.238, resulting in removing particles with sizes larger than 1 μm at an aerosol flow rate of 1.5 lpm. The thermophoretic particle collection efficiency in the prototype was measured without the size-selective inlet installed. The size dependence of the collection efficiency was negligible for particles with diameters ≤300 nm and became noticeable for those with diameters >300 nm. An analytical model was further developed to estimate the particle collection efficiency due to thermophoresis of the prototype under various aerosol flow rates and temperature gradients. For particles with diameters less than 400 nm, reasonable agreement was obtained between the measured data and the collection efficiency calculated from the developed analytical model. It was further concluded that the derived formula for the calculation of thermophoretic particle collection efficiency could serve as the backbone for future design of thermal precipitators in any configuration, when combined with the proper formula for the dimensionless thermophoretic particle velocity.

Copyright 2012 American Association for Aerosol Research     

Use of carbon nanotube filter in removing bioaerosols

In this study, the carbon nanotube (CNT) filters were created by depositing both single-walled and multi-walled CNT on polypropylene and polyamide membrane supports. The physical efficiencies of the CNT filters with different CNT loadings when removing the aerosolized Bacillus subtilis var niger, Pseudomonas fluorescens and NaCl were studied using an optical particle counter together with a button aerosol sampler.The removal efficiencies of CNT filters prepared on polypropylene membrane supports of 10 μm pore size when collecting B. subtilis var niger aerosols were shown to range from 10% to 95% in average for the CNT loadings of 0.2–1.6 μg/cm². When collecting aerosolized P. fluorescens, the efficiencies were shown to range from 5% to 60% given similar CNT loadings used. The results revealed that particle types and CNT loading had greater effects on the efficiencies than the membrane types and pore sizes tested. When collecting aerosolized NaCl, the efficiencies were observed relatively lower, i.e., below 50% for loadings of 0.3–1.5 μg/cm². Acid-rinsing was shown to exhibit statistically significant effect on the removal efficiency of single-walled CNT filters when collecting aerosolized NaCl. Multi-walled CNT filters were shown to perform better than single-walled CNT filters. The performances of CNT filters prepared were observed to vary greatly, which was likely due to the CNT loading efficiency, membrane support filtration variance and the CNT uniformity on the support. The information obtained here can be used to develop future indoor air pollution control measures.     

Design and Characterization of a New Coarse Particle Collector Based on Microtrap Impactor Technology

A microtrap inertial impactor has been developed and characterized for use as an area or personal sampler. The microtrap impactor utilizes a high-density multijet plate to direct airflow and a matched multiwell plate to impact and collect particles for extraction with a reduced pressure drop relative to inertial impactors with fewer jets. Reported here is the characterization of the microtrap impactor using a fluidized bed aerosol generator and a small volume nebulizer to generate particles of Arizona Road Dust, potassium chloride, and oleic acid. Collection efficiency was determined by measuring particle size distributions with an aerodynamic particle sizer. Two geometries of the microtrap were tested suitable for a two-stage coarse particle sampler, with 1–4 μm and a 4–10 μm stages. The 1 μm cut-point microtrap stage has a collection efficiency above 97% for particles greater than 2 μm in diameter (at a 10 L/min flow rate and a pressure drop of 0.12 kPa). This stage's collection efficiency was constant for a period of time up to 10 h under typical ambient conditions without any coating on the impaction surface. The microtrap impactor provides an improvement in area sampling due to its high collection efficiency at a low pressure drop across the device, and its use of an uncoated impaction surface allowing for the extraction and analysis of biological samples.

© 2013 American Association for Aerosol Research     

Fabrication of multilayer glassy ceramic filters by fine particle migration during slip casting

Cylindrical, glassy ceramic filters with multilayer compaction, consisting of filtration layers of varied pore sizes on granular assemblies with specific interlayers, were shaped by a fine particle migration phenomenon during slip casting. The interlayer provided structural integrity of the filter material and thus the occurrence of the fine particle migration is vital for the success of the casting process. The production of non-crack, dry compaction was investigated from the experiments, which were designed to systematically combine varied sizes of mixture powder particles (quartz–zeolite–frit glass) and its granules. This technique can be applied to the production of ceramic filters with the median pore size of about 0.35 μm. The problem in dealing with finer pore sizes is in the fabrication process: a low casting rate is obtained with finer particles, which results in a low viscous drag on the particles, preventing particle migration.     

Recovery of Water from Sewage Effluents using Alumina Ceramic Microfiltration Membranes

Abstract

This work highlights the recovery of water from sewage effluents using alumina ceramic membranes with pore sizes of 0.2 and 0.45 µm respectively in dead‐end filtration mode. The work demonstrates the ability and advantages of alumina‐based microfiltration (MF) membranes in filtering microbes and other harmful pollutants normally present in sewage effluents in dead‐end filtration mode. The fouling behavior of the membranes in the filtration cycle is identified, which in turn helped to regenerate the fouled membranes for subsequent usage. Regeneration studies of fouled membranes also suggest that though chemical cleaning was effective in recovering membrane performance, the fouling had still been progressed slowly and the membranes showed the ability to perform at least five filtration cycles of highly‐contaminated sewage effluents. As expected, the filtration efficiency and flux characteristics at various transmembrane pressure (TMP) of the membranes varies with the pore size of the membrane and is explained in light of Darcy's and Poiseuille's laws of filtration. The results show that alumina ceramic membrane with disc geometry having a pore size of 0.2 µm is more effective in filtering the total suspended solids, turbidity and microbes of the sewage effluents as compare to that of 0.45 µm membrane to a level in which the permeate water appears to be benign for discharging into the surface thereby offering the possibility of recycling or reusing the recovered water from the sewage effluents for suitable purposes.     

Evaluation of Particle Bounce in Various Collection Substrates to be Used as Vaporizer in Aerosol Mass Spectrometer

The determination of the collection efficiency (CE) of particles during transport, vaporization, and ionization in the aerosol mass spectrometer (AMS), which uses vaporizer to evaporate non-refractory particles with subsequent ionization, is important for accurately quantifying the concentrations of chemical constituents. Particle bounce in the vaporizer can be considered as one of the most important parameters influencing the CE of particles. Substrates with various shapes (flat, cylindrical, reverse-conical, cup, trapezoidal, and reverse-T), materials (stainless steel, copper, tungsten, and molybdenum), pores with average sizes of 0.2, 1, 5, 20, and 100 μm, and mesh with a size of 79 μm, which can be a possible candidate for the vaporizer in the AMS, were constructed. Bounce fractions of sub-micrometer particles (polystyrene latex, oleic acid, and dioctyl phthalate) were determined using the differential mobility analyzer (DMA)-impactor technique under a constant impact velocity. For the porous substrate, the particle bounce fraction significantly decreased with increasing pore size and porosity, but there was an upper limit for the pore size above which the particle bounce fraction no longer decreased significantly (i.e., the rebounded particles successfully escaped from the pores). The mesh substrate also had a lower particle bounce fraction than the flat substrate. Among the tested materials, the copper substrate having the lowest hardness and elasticity had the lowest particle bounce fraction. In addition, the reverse-T shape substrate having more available surfaces for particle entrapment led to the reduction of particle bounce fraction. In terms of phase, the liquid particles had lower particle bounce fractions than the solid particles. Our results suggest that the vaporizer in the AMS should provide traps for multiple collisions of the rebounding particles with an appropriate porosity or mesh and should be made of low-hardness materials to minimize particle bounce.

Copyright 2015 American Association for Aerosol Research     

Studies on Transport of Anionic Complex of Plutonium From Nitric Acid Medium across ALIQUAT 336/n-Paraffin Liquid Membrane

The present studies deal with the application of the supported liquid membrane (SLM) technique for the separation and purification of plutonium from other impurities in nitric acid medium using anion exchanger Aliquat 336 (a quaternary ammonium salt)/ n-paraffin as a carrier. The effects of feed acidity, stripping agent, and membrane pore size and membrane thickness on the transport behavior of anionic complex of plutonium have been studied in detail. An attempt has been made to establish the mechanism for plutonium transport and model the physicochemical transport of plutonium across SLM. Transport of anionic complex of plutonium increased with increase in carrier concentration upto 10% (w/v), while with further increase in carrier concentration, decrease in transport of plutonium was observed. The PTFE membrane with 0.45 µm pore size and 80 µm thickness was found to be most suitable for the transport of plutonium. The effect of membrane thickness indicates that the transport phenomenon is diffusion controlled. Transport behavior of plutonium, uranium, and other fission products from actual feed solution of ion exchange method obtained in PUREX process was also tested and the result clearly indicates that Aliquat 336 has high selectivity for plutonium and it can be used for the separation and purification of plutonium by the supported liquid membrane technique.     

一体化陶瓷外膜乳化装置制备O/W型乳状液

引　言膜乳化技术是将分散相以很小的压力压过膜孔 ,在膜表面形成微小的液滴 ,并通过剪切力的作用使小液滴从膜表面脱落而进入连续相的新型乳化技术 .该方法具有低能耗、低剪切力、需要表面活性剂较少、生成的乳液颗粒均匀等特性[1,2 ] ,所用的膜主要有微孔玻璃膜[3] 和陶瓷膜两种[4 ] .微孔玻璃膜的孔径分布较窄 ,通常在小于平均孔径±15 %的范围内变化 ,因此制备出的乳状液粒径分布较窄 ,但对称膜固有的高阻力导致膜的通量较小(通常在 2～ 4 0L·m- 2 ·h- 1) ,制约了其在工业领域的应用 .而陶瓷膜由于具有较高的通量被较多地用于工业化…     

Sampling efficiencies of two modified viable cascade impactors

Prevention of airborne contagious diseases depends on successful characterization of aerosols in the environment. The use of cascade impactors to characterize ambient aerosols is one of the most commonly used methods, providing data on both particle size and concentration. In this study, the use of a cascade impactor recently described in the literature using 8 mL of liquid in Petri dishes (CI-L) was compared with a new method that uses wet membrane filters on top of wax filled Petri dishes (CI-WWMF). Sampling efficiencies of the cascade impactors were evaluated using 0.5, 1, 3, and 5 μm polystyrene latex (PSL) microspheres and aerosol consisting of single spores of Bacillus atrophaeus var. globigii (BG). The sampling efficiency of the CI-L was 6%, 11%, 17%, 21%, and 58% for 0.5, 1, 3, 5 μm PSL microspheres and BG spores, respectively. Higher overall sampling efficiencies of 71%, 91%, 60%, 64%, and 104% were observed for the same size and type of particles for the CI-WWMF. This study indicates that using wet filters on top of wax-filled Petri dishes (CI-WWMF) in a viable cascade impactor is more efficient than the CI-L method for size-selectively collecting biological aerosols from the environment. The CI-WWMF method is useful when a liquid medium is required for identifying and quantifying organisms using polymerase chain reaction (PCR) and immuno-assay techniques.

Copyright © 2017 American Association for Aerosol Research     

Wastewater filtration performance of multilayer glassy microporous filters

The glassy composition (quartz, clinoptilolite and frit glass mixture) provides a filter having glassy pore wall microstructure and thus enables easily cleaning through the filter recovery by back flushing. The filter was obtained as multilayer compaction by one step slip cast-processing where a cylindrical filter, consisting of filtration layer on granular assemblies with specific interlayer was shaped by a fine particle migration phenomenon. The multilayer compaction has low resistance to liquid flow and thus the filter great potential to use for wastewater filtration. It is known that high capacity filtration also requires correct pore size/interval with respect to filtered particles. In this study, a wastewater overflow from marble factory (0.035 wt.% of solid with a size distribution of 0.58-1.46 μm) was filtered by different pore sizes of the glassy filters (pore size intervals: 0.4-10 μm, 0.2-4 μm, 0.1-1.5 μm and 0.04-2 μm) and significantly different filtering capacities was obtained; the irreversible fouling capacities were determined between 2.9 and 8.5 m³ of filtrate per m² of the filter area through the filtration produced 5 min intervals. The filtration pressure was 5 bar and backflushing was achieved at 1 bar. The high filterability (8.1 m³/m² in 5 min) with high filtrate clarity (∼0.5 nephelometric turbidity units) could be obtained using finer pore sized filters. The large size filter was seriously clogged during the filtration.     

The effect of particle size distribution on the microstructure and properties of Al2O3 ceramics formed by stereolithography

Stereolithography (SL) shows advantages for preparing alumina-based ceramics with complex structures. The effects of the particle size distribution, which strongly influence the sintering properties in ceramic SL, have not been systematically explored until now. Herein, the influence of the particle size distribution on SL-manufactured alumina ceramics was investigated, including bending strength at room temperature, post-sintering shrinkage, porosity, and microstructural morphology. Seven particle size distributions of alumina ceramics were studied (in μm/μm: 30/5, 20/3, 10/2, 5/2, 5/0.8, 3/0.5, and 2/0.3); a coarse:fine particle ratio of 6:4 was maintained. At the same sintering temperature, the degree of sintering was greater for finer particle sizes. The particle size distribution had a larger influence on flexural strength, porosity and shrinkage than sintering temperature when the particle size distribution difference reached 10-fold but was weaker for 10 μm/2 μm, 5 μm/2 μm and 5 μm/0.8 μm. The sintering shrinkage characteristics of cuboid samples with different particle sizes were studied. The use of coarse particles influenced the accuracy of small-scale samples. When the particle size was comparable to the sample width, such as 30 μm/5 μm and 5 mm, the width shrinkage was consistent with the height shrinkage. When the particle size was much smaller than the sample width, such as 2 μm/0.3 μm and 5 mm, the width shrinkage was consistent with the length shrinkage. The results of this study provide meaningful guidance for future research on applications of SL and precise control of alumina ceramics through particle gradation.     

Development of Variable Flow Rate Isokinetic Sampling System for 0.5–15-μm Aerodynamic Diameter Particles

Isokinetic sampling is required when evaluating the aerodynamic sizes of particles released from dry powder inhalers (DPI) under simulated breathing condition since anisokinetic sampling may lead to significant sampling error for coarse particles. We propose an isokinetic measuring system for aerosol particles from a stream in a narrow conduit of variable flow rates (variable flow rate aerosol sampler, VFAS) combined with Aerodynamic Particle sizer® APS^TM spectrometer (model 3321, TSI Inc.). The VFAS was capable of generating variable sampling flow rates by adjusting the flow resistance of makeup air to produce constant flow rate of aerosol to the APS. The penetrations through the VFAS-APS system were measured using monodisperse particles with a size range of 0.7–15 μm by applying a rectangular flow rate–time pattern of sampling air, and we found that the VFAS-APS system can measure the number concentration of particles with the particle detection efficiency (particle penetration through the system) of almost unity. The VFAS-APS system may be a powerful tool to measure the size and concentration of powder released by the DPI in the size range of 0.5–15 μm.

Copyright 2012 American Association for Aerosol Research