Aerosol Deposition in Sampling Probes

Deposition of aerosol particles on the inner walls of sampling probes is of concern in many aerosol sampling applications. Only inertial and gravitational effects have been considered in previous studies of the aerosol deposition; however, the lift force on particles is also of significance. In this investigation, experiments have been conducted to construct a database for aerosol deposition in Willeke-type sampling probes. An empirical correlation has been made between wall losses and the depositional forces of drag, gravity, inertia, and particle lift through the use of dimensionless parameters. Inclusion of the lift effect in this correlation not only helps to better predict particle behavior in the sampling inlet, but it also provides a basis for understanding of the intrinsic deposition phenomenon. The correlation has a geometric standard deviation of 1.13 and a 0.93 correlation coefficient relative to the experimental data.     

Stratospheric Aerosol Sampling: Effect of a Blunt-Body Housing on Inlet Sampling Characteristics

During a campaign to study ozone loss mechanisms in the Arctic stratosphere (SOLVE), several instruments on NASA's ER-2 aircraft observed a very low number density (0.1 I^?1) of large, nitric-acid-containing particles that form the polar stratospheric clouds (PSCs). For effective physical and chemical characterization of these particles, the measurements from these instruments have to be intercompared and integrated. In particular, proper interpretation requires knowledge of the sampling characteristics of the particles into the instruments. Here, we present the calculation of the sampling characteristics of the one of the instruments on the ER-2, the NOAA NOy instrument. This instrument sampled ambient particles and gas from two forward-facing inlets located fore and aft on a particle-separation housing (the football) and measured total NOy in the sample. In recent studies, ambient aerosol mass has been estimated by the difference of the measurements of the two inlets with the assumption that the rear inlet observations represent the gas-phase NOy and small particles and the front inlet samples represent gas-phase NOy and all particle sizes with varied efficiency (anisokinetic sampling). This knowledge was derived largely from semiempirical relations and potential flow studies of the housing. In our study, we used CFD simulations to model the compressible flow conditions and considered noncontinuum effects in calculating particle trajectories. Our simulations show that the blunt body housing the inlets has a strong and complex interaction with the flow and particles sampled by the two inlets. The simulations show that the front inlet characteristics are influenced by the effect of the blunt body on the upstream pressure field. The rear inlet sampling characteristics are influenced both by the shape and size of the inlet and its location on the blunt body. These interactions result in calculated inlet characteristics that are significantly different from previously assumed values. Analysis of the SOLVE data, considering the ambient conditions and the calculated inlet sampling characteristics, in conjunction with thermodynamic growth modeling of super-cooled ternary solution (STS) particles, provides validation of the CFD results.     

Ultrafine Particle Sampling with the UNC Passive Aerosol Sampler

A model is presented to describe the collection of ultrafine particles by the UNC passive aerosol sampler. In this model, particle deposition velocity is calculated as a function of particle size, shape and other properties, as well as a function of sampler geometry. To validate the model, deposition velocities were measured for ultrafine particles between 15 and 90 nm in diameter. Passive aerosol samplers were placed in a 1 m ³ test chamber and exposed to an ultrafine aerosol of ammonium fluorescein. SEM images of particles collected by the samplers were taken at 125 kX magnification. Experimental values of deposition velocity were then determined using data from these images and from concurrent measurements of particle concentration and size distribution taken with an SMPS. Deposition velocities from the model and from the experiments were compared and found to agree well. These results suggest that the deposition velocity model presented here can be used to extend the use of the UNC passive aerosol sampler into the ultrafine particle size region.     

Very High Volume Aerosol Sampling with a Novel Drum Centrifuge

For chemical analysis of trace compounds, comparatively large amounts of dust have to be collected. If good time resolution is required, very high sampling flow rates are mandatory. The operating principle of the drum centrifuge built to cope with these requirements is based on particle deposition on the inner surface of a porous rotating drum. Due to the rotation, a pressure gradient draws the aerosol into the bore of the axis and from there radially outward through a number of holes into the drum. The aerosol then moves to the periphery of the double-walled drum, which consists of two 0.15-mm-thick metal sheets with 1-mm spacing. Each of these metal sheets is perforated by several rows of small slits resulting in porosity of 16%. The slits in the inner and outer sheet are displaced, so that the particles will be strongly deflected on their way out of the rotating drum. Under the combined action of centrifugal forces and strong streamline deflection in the displaced slits of the two thin-walled drums, the particles are deposited. Flow rate as a function of rpm and collection efficiency as a function of particle size were determined experimentally. For simplicity, only the flow field of two (nonrotating) displaced slits was mathematically analyzed. The resulting 2-D solution of the Navier-Stokes equation was used for deterministic limiting trajectory calculations in the case of large particles. Diffusional motion of small particles was allowed for by Monte Carlo trajectory calculation. The calculated deposition efficiencies agree satisfactorily with the experimental results. At 3000 rpm a flow rate of 1200 m³/hr and efficiencies of 91% for 2.1-μm particles, 75% for 0.6-μm particles, and 48% for 0.04-μm particles were obtained. For easy extraction of the collected particulate matter, the device is equipped with an ultrasonic cleaning bath.     

Size-Resolved Penetration Through High-Efficiency Filter Media Typically Used for Aerosol Sampling

We have developed a new, fully controlled filter testing device and have used it to measure size-resolved penetration through a typically used filtration media for (but not only) atmospheric aerosol sampling. Twenty membrane and fiber filter pieces (mixed cellulose ester filters, polytetrafluoroethylene filters, quartz fiber filters, glass fiber filters, and polycarbonate filters) of various manufacturers and filter codes were examined. High variability in the penetration curve shapes, most penetrating particle size (MPPS) (from 20 nm to 90 nm) and penetration maxima (from 0.001% to almost 100%) has been found. The dependence of pressure drop on face velocity generally agrees with theory, the comparison of penetration at various face velocities proved the theoretical equations being able to determine MPPS only partially correctly. Although the variability within an individual filter of the same code is not negligible, it is small compared to the differences between the various filter types. The results not only differed from the information provided by the manufacturers, but in many cases also provided information otherwise unavailable, although affecting the sampling and also the ability of comparison with theory. To have enough information for the proper choice of the filter for a given purpose, it would be necessary to have not only total penetration given from the DOP standard measurement, but the MPPS, penetration maximum value and pressure drop as well.

Copyright 2015 American Association for Aerosol Research     

Behavior of Alkali Metal Aerosol in a High-Temperature Porous Tube Sampling Probe

Two-component model aerosols consisting of KCl vapor and ultrafine K₂SO₄ particles were generated in the laboratory to study sample behavior in a high-temperature porous tube sampling probe. The conditions were set to represent those typically occurring at biomass-fired furnaces. Particle size distributions were measured from the diluted aerosol via several sampling parameters and the temperature and mixing conditions inside the diluting probe were characterized. The experimental findings were interpreted by one-dimensional aerosol dynamics modeling. Gaseous KCl was found to form very small KCl particles inside the diluter by homogeneous nucleation. In the cases where K₂SO₄ seed particles were introduced into the sample, part of the KCl vapor condensed on the seeds, while the remainder formed a clearly distinct nucleation mode due to the relatively high cooling rates in the probe. In the studied probe, mixing of sample and dilution gas was relatively fast, which was found to be favorable for KCl nucleation. The condensation behavior of KCl in the probe with simultaneous dilution and cooling was found to be clearly influenced by mixing, cooling, and surface area of the existing particles. The results show that in the porous tube diluter, different sampling parameters can be used either to enhance the appearance of nucleation mode, or to promote condensation of vapors on existing particles to minimize sample losses on walls. Furthermore, these results point to the possibility to design a high-temperature sampling system, which minimizes the artifacts caused by vapor condensation on existing fine particles during sampling.

Copyright 2012 American Association for Aerosol Research     

Investigation of Filter Bypass Leakage and a Test for Aerosol Sampling Cassettes

Plastic filter cassettes (37 and 25 mm), which are press fitted together to seal and hold a filter in place, are commonly used for sampling aerosols. Aerosol bypass leakage around the filter has been reported by several researchers and attempts have been made to test for leakage and to reduce the likelihood of leakage by improving cassette design. Under typical sampling conditions, there is often no indication to the user that leakage may have occurred. In the present study, a particle count leak test was developed that used a particle counter that measured the particle number concentration of ambient aerosol (primarily submicrometer particles) upstream and downstream of the filter cassette. The relationship between leak test results and particle loss from the filter depended on particle size and type in a complex fashion. The mechanisms of particle loss were investigated and the losses increased for particles above 2 w m and were much greater for solid and fume aerosols than for oil droplets. Although the test could not be used to predict particle mass loss during sampling, the test was a sensitive indicator of cassette bypass leakage and was used to establish compression pressures needed for proper assembly of these cassettes.     

Comparative Study of Pressure Reducers for Aerosol Sampling from High Purity Gases

A performance evaluation and comparative study has been conducted with six pressure-reducing devices suitable for particle sampling from high pressure gas systems. Pressure-reducing devices are used to reduce the gas pressure from that existing in the high-purity compressed gas system to ambient conditions for subsequent measurement of particulate contaminants by particle counters. Six pressure-reducing devices, including designs based on the orifice plate, orifice design with expansion cone, and capillary tube designs, have been evaluated experimentally to determine their particle penetration characteristics and contribution to background particle.

Studies showed that particle loss in pressure reducers depended upon the pressure-reducing geometry, gas pressure and particle size. Particle penetration through orifice type devices was found to be superior to that found for capillary tube type devices. The 50% penetration through orifice type pressure reducers was found to be at a particle diameter of approximately 3.0 μ while for the capillary tube designs at a particle diameter less than 1.0 μ. For the orifice-type pressure reducers the particle background concentration was less than 0.05 particles/ft³ (1.77 particles/m³). Significantly higher particle background levels were found for the capillary tube type devices which is believed to result from particle reentrainment from the capillary tube wall.     

Evaluation of a Perpendicular Inlet for Airborne Sampling of Interstitial Submicron Black-Carbon Aerosol

The majority of airborne aerosol measurements employ forward-facing inlets with near-isokinetic sampling; these inlets have known artifacts when sampling in clouds such that data taken in cloud must typically be discarded. Here we report first results from a perpendicular inlet for sampling interstitial submicron black-carbon (BC) containing aerosol. The inlet, consisting of a flat plate to stabilize flow prior to perpendicular sampling, was evaluated using a single particle soot photometer (SP2) aboard the NASA WB-57F aircraft during the Midlatitude Airborne Cirrus Properties Experiment (MACPEX) of 2011. The new inlet rejects large particles and is free of aerosol artifacts when sampling in ice clouds while allowing sampling of submicron BC-containing aerosol with the same unit efficiency as a validated isokinetic inlet, thus allowing for airborne sampling of interstitial BC aerosol.

Copyright 2013 American Association for Aerosol Research     

Anisokinetic Shrouded Nozzle System for Constant Low-Flow Rate Aerosol Sampling from Turbulent Duct Flow

An anisokinetic shrouded nozzle system was designed for sampling particles at a constant low flow rate from a ventilation duct to an aerodynamic particle sizer (APS). Shrouded anisokinetic nozzles are a means for sampling from a moving airstream with higher particle transmission than with unshrouded isokinetic nozzles. This shrouded nozzle sampling system was evaluated in an experimental ventilation duct system. Aspiration and transport efficiency measurements were made for five particle sizes in the range 1–13 μm at each of three duct air speeds in the range 2.2–8.8 m/s. Under these conditions, the shrouded nozzle system showed improved performance compared to buttonhook isokinetic nozzles, especially for larger particles and higher air speeds. Measured transmission efficiencies through the shrouded nozzle sampling system were generally higher and more reliably predictable than those through buttonhook isokinetic nozzles. Model predictions of transport and aspiration efficiencies of the shrouded nozzle system showed good agreement with measurements over the entire range of experimental conditions. The shrouded nozzle sampling system could be used to measure concentrations in ventilation ducts with an APS for particles in the diameter range 1–13 μm.

Copyright 2014 American Association for Aerosol Research     

Design and Operation of a Pressure-Controlled Inlet for Airborne Sampling with an Aerodynamic Aerosol Lens

Two pressure-controlled inlets (PCI) have been designed and integrated into the Aerodyne Aerosol Mass Spectrometer (AMS) inlet system containing an aerodynamic aerosol lens system for use in airborne measurements. Laboratory experiments show that size calibration and mass flow rate into the AMS are not affected by changes in upstream pressure (P ₀ ) of the PCI as long as the pressure within the PCI chamber (P _PCI ) is controlled to values lower than P ₀ . Numerous experiments were conducted at different P _PCI , P ₀ , and AMS lens pressures (P _Lens ) to determine particle transmission efficiency into the AMS. Based on the results, optimum operating conditions were selected which allow for constant pressure sampling with close to 100% transmission efficiency of particles in the size range of ～ 100–700 nm vacuum aerodynamic diameter (d _va ) at altitudes up to ～ 6.5 km. Data from an airborne field study are presented for illustration.     

Use of Numerical Calculations to Simulate the Sampling Efficiency Performance of a Personal Aerosol Sampler

Numerical calculations were conducted to simulate air and particle behavior near and into the inlet of an aerosol sampler in order to determine sampling efficiency performance. This was done with the pre-verified commercial computational fluid dynamics (CFD) software package, FLUENT (Fluent, Inc., Lebanon, NH, US). Air flow behavior was calculated for steady-state conditions approaching and flowing into 3D geometries of an aerosol sampler free in the air that was similar in dimension to two commercial samplers, namely the Gesamtstaubprobenahme sampler (GSP) and the conical inhalable sampler (CIS). Particle trajectories were calculated in a Lagrangian reference frame on the resulting velocity fields. Based on the particle trajectories, sampling efficiencies were calculated and compared to those reported in the literature for a CIS aerosol sampler. They were found to have similar overall trends for particle sizes up to 21 μ m. Using a correction factor, agreement was observed to be very good for smaller particles, but less so for larger particles.     

Freitag:把篷布挎上街

会有人用2000块钱买一块废旧的汽车篷布吗?当然。木村拓哉就是其中之一。第一眼看到佛莱塔的包,是木村拓哉在《ENGINE》里那款黄色。当时怀疑那是用了几年的旧货,却又觉得古旧和磨损的痕迹有一种恰到好处的美感。背带是宝马车的安全带,包身皮质是货车的防雨漆布,还有很多自行车零件元素,每一只包都是独一无二。这就是佛莱塔兄弟用收集废旧的卡车防水布和汽车安全带制作的邮差包,环保与时尚的完美结合让它们风靡欧洲,被年轻的设计师和潮人疯狂迷恋。     

Characterization of the Velocity Field in a Small,Cylindrical, Low Reynolds Number Aerosol Sampling Cyclone

A laser Doppler velocimeter capable of simultaneously measuring two components of velocity was used to measure the flow field in a 88.9-mm diameter, cylindrical, reverse-flow, multiport cyclone. A third component was measured by reorienting the cyclone. The components measured were those in the radial, axial, and tangential directions with the tangential component being measured in both orientations. The ratio of velocities was ? _θ:? _z:? _R = 100:10:1. At a flow-rate Reynolds number, N _RQ= (4pQ)/(πμD _c), of approximately 860, values of turbulence intensity for each component within the cyclone were on the order of 10% when determined as the component standard deviation normalized to the mean flow. The vortex structure is dependent upon Reynolds number.     

A Model for the Prediction of the Collection Efficiency Characteristics of a Small,Cylindrical Aerosol Sampling Cyclone

Velocity data from a previous study were nondimensionalized and used in conjunction with a computer program which solves the equations for particle trajectory to predict the collection efficiency for the cyclone. Results for the prediction of cutpoint at the same Reynolds number as that for which the velocities were measured, both for a large cyclone of 88.9 mm diameter and another geometrically similar at one half the scale, are excellent. The model predicts cutpoints of 10 μm and 5.1 μm for the large and small cyclone, respectively, while the actual cutpoints determined from aerosol tests were 9.9 μm and 5.2 μ m. The efficiency curve generated by the model was steeper (geometric standard deviation of 1.1) than the efficiency curve determined through the aerosol testing (geometric standard deviation of 1.4). A simplification of the Dirgo and Leith equation fitting Barth's design curve is suggested which provides a significantly better fit of the aerosol data (geometric standard deviation of 1.3). At 1.5N _{R Q}, where N _{R Q} = (4pg)/(πμD _c), the error in prediction of the cutpoint in the large cyclone is less than 8% while at 04N _{R Q} the error is less than 2%. Although results are good over a limited range of Reynolds numbers, the model is strictly applicable only for flows which are dynamically similar to those studied here.     

A New Aircraft Inlet for Sampling Interstitial Aerosol: Design Methodology,Modeling, and Wind Tunnel Tests

The design of a new aerosol sampler, called the blunt-body aerosol sampler (BASE), to sample interstitial particles inside clouds while avoiding the problem of cloud droplet shatter artifacts is introduced. The primary design feature of the inlet is a blunt body that houses an aerosol inlet toward its aft end. The housing is designed to be blunt enough to deflect large cloud particles traveling around the body while being streamlined enough to maintain an attached boundary layer under aircraft flow conditions. The attached flow requirement ensures that shatter particles formed from the impaction of cloud droplets on the blunt body are retained close to the surface of the body. A region of large particle shadow is, thus, created in the aft of the blunt-body housing, where an aerosol inlet can sample interstitial particles in the absence of cloud particles. Computational fluid dynamics (CFD) simulations are used to optimize the shape of the blunt body, and the final sampler design is predicted to sample particles smaller than 2 μm from the freestream while being uninfluenced by cloud droplet shatter particles of the same size. Wind tunnel tests were performed on a prototype model to confirm the attached nature of the boundary layer flow around the blunt body and to establish the size-dependent behavior of shatter particles in the vicinity of the housing. While the experiments provide initial validation of the interstitial inlet design concept, some discrepancies were observed between the wind tunnel tests and CFD predictions, suggesting a need for improvements in simulations, inlet design, and/or test methodology. Initial analyses of field data obtained from the first aircraft deployment of BASE confirm that sampling of shatter-free interstitial aerosol is possible with the inlet, but full performance characterization of BASE will require significant additional aircraft-based experiments under a range of cloud conditions.

Copyright 2013 American Association for Aerosol Research     

纺织品中户外睡袋的发展研究

介绍了户外睡袋的类型、面料、填充料等,探讨了睡袋的保暖性,并指出其发展方向及存在的问题,认为国内相关标准的缺失阻碍了户外装备的发展。     

用滤膜压力降法研究气溶胶发生器输出浓度的稳定性

先行研制的振筛进料流化床气溶胶发生器的稳定性能不够理想,需要对其进行改进. 根据气溶胶在滤膜上沉积量与压力降的关系,通过测量采样滤膜两端压力降,对发生器发生浓度的稳定性进行了表征. 对流化床气溶胶发生器进料稳定性的影响因素进行了讨论,研究了进气流量和进料斗中硅胶加入量对稳定性的影响. 测试结果表明,进料斗中加入1~3层硅胶、进气流量800~1000 L/h时,发生器发生浓度的稳定性最好.     

水乳型果实袋胶粘剂的研究

本文研究了水乳型果实袋胶粘剂的制备及性能。把乙烯基树脂溶解后，经改性、乳化处理，得到一种初粘度高、流动性好的乳液。该乳液用于涂蜡纸的高速（10，000个／小时）粘合，成袋率高。制成的果实袋在田间自然侵蚀三个月不开胶。