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1.
An aerosol dynamics model for dry deposition process is developed based on the moment method. Since it is hard to fully apply the moment method to the widely used dry deposition velocity expressions based on the resistance theory, the dry deposition velocity expression by Raupach et al. (2001) is used. Detailed deposition mechanisms such as Brownian diffusion, gravitational settling, and impaction are considered in the expression. To verify the validity of the derived dynamic equation, aerosol dynamics for the dry deposition process is estimated with the expressions of Raupach et al. (2001), of Wesely (1989) modified for particles (Seinfeld and Pandis 1998), in CMAQ, and with constant value used in RAINS-ASIA. Those expressions give different dynamics. Generally, the result for this study is between the result of modified Wesely's expression and CMAQ. When using the modified Wesely's expression with the number of sections being equal or smaller than 10, the resultant size distribution does not give the peak shape accurately. 相似文献
2.
A general methodology is presented that enables rigorous estimation of the total collection efficiency and the size distribution of particles penetrating dust control systems. This methodology assumes lognormal inlet particle-size distributions and can be used with fractional efficiency formulations that predict, under such conditions, lognormal outlet particle-size distributions. Multimodal inlet particle distributions can be accommodated additively. This methodology is applied to Electrostatic Precipitator Systems (ESPs), with the Nobrega et al. (2004) model selected for predicting their fractional efficiencies. For ease of use, a graphical solution has been developed for the Nobrega et al. fractional efficiency relations, but its availability is not a prerequisite for the application of the general methodology. For the latter, the fractional efficiencies corresponding to three particle diameters need to be estimated and this can be done either graphically or numerically using the model of Nobrega et al. or any other fractional efficiency formulation of interest. Fine particles emerge as the most important pollutant worldwide in terms of human health, creating thus the need for credible particle size-specific inventories. In line with the above, a generic and rigorous method, capable of producing size-specific emission estimates from uncontrolled and controlled sources, has been developed (Economopoulou and Economopoulos 2001). For controlled sources, this method relies on the development of easy to use models that predict the total efficiency and the lognormal size distribution of particles penetrating the control systems used. Such models have already been developed for dry cyclone separators (Economopoulou and Economopoulos 2002a, 2002b) and venturi scrubbers (Economopoulou and Harrison 2007a, 2007b). The present methodology extends the use of the inventory methodology to ESP-controlled sources and, in addition, it provides a generalized basis for covering other types of control systems with any fractional efficiency formulation considered appropriate. 相似文献
3.
S. J. Dunnett X. Wen S. K. Zaripov R. S. Galeev M. V. Vanunina 《Aerosol science and technology》2013,47(7):490-502
The performance of an idealized spherical sampler facing both vertically upwards and downwards in calm air is studied numerically. To describe the air flow around the sampler, both potential and viscous flow models have been adopted. The equations of particle motion are then solved to calculate the aspiration efficiency. The dependence of the aspiration efficiency upon the various parameters of importance in calm air sampling are investigated and compared where possible with the experimental work of Su and Vincent (2003, 2004a, b). It is found that in the case of upwards sampling the bluntness of the sampler only has a significant effect upon aspiration for large sampling velocities, values that would not generally be physically realistic. In the case of downwards sampling an important non-dimensional quantity, B 2 R C , is identified, where B represents the sampler bluntness and R C represents the gravitational effects. This quantity determines the physical conditions for which aspiration will not occur and also the limiting values of the aspiration efficiency when aspiration does occur. In the case of low sampling velocities a difference is noted between experimental and numerical results for aspiration efficiency raising the need for more experimental data in this area. For both upwards and downwards sampling the semi-empirical models of Su and Vincent (2004b) have been modified to account for the information gained from the study. This is particularly important in the downwards sampling case where the modified model is found to agree particularly well with the results obtained. 相似文献
4.
《Journal of Sulfur Chemistry》2013,34(2):223-229
Herein, the chemistry of 2-aminothiophenol has been utilized in the synthesis of several interesting products such as oxidation and reaction with π-deficient compounds. On oxidizing 2-aminothiophenol by sodium hypochlorite furnishes 2-[(2-aminophenyl)-dithio]aniline. Treatment of the obtained product with acetyl chloride affords N-(2-[2-(acetylamino)-phenyl-disulphanyl)-phenyl]acetamide. Reaction of the former acetamide with POCl3 yields 2-methyl-1,3-benzothiazole. Moreover, (3,4,8,9)-dibenzo-2,7-dithia-5,10-diaza4 4 4propellane is formed on reacting the target 2-aminothiophenol with cyclohexane-1,2-dione, whereas its reactions with electron π-acceptors such as 2,3-dichloro-1,4-naphthoquinone (DCHNQ), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), tetra-cyanoethylene (TCNE), and 1-(dicyanomethylen)acenaphthen-2-one yield various heterocycles. 相似文献
5.
Daryl L. Roberts 《Aerosol science and technology》2013,47(11):1119-1129
We describe a general theory of multi-nozzle cascade impactor stages and show how testers of inhaled drug products, such as metered-dose or dry-powder inhalers, can decide, solely from the stage nozzle dimensions, whether any used impactor is satisfactorily operating within its expected aerodynamic performance range. We first account for the realistic shape of particle collection efficiency curves and show that the effective diameter, described by Roberts and Romay (2005), is sufficiently accurate as the primary indication of the aerodynamic performance.To ensure that a used impactor is performing in the same aerodynamic range allowed for new impactors, one must also satisfy the other, more secondary factors of cascade impaction aerodynamics, most notably the distance to the collection surface relative to the nozzle diameter. We show what this constraint means in practice for used Next Generation Impactors (NGIs; Marple et al. 2003a, b; 2004), and show that partially occluded nozzles are the most likely nozzles to fail this test.Applying this principle that used impactors should perform in the same aerodynamic range as new impactors, we derive constraints on the nozzle diameters of any used NGI (Table 6, main text). We can partially apply this principle to other common impactors used for inhaler testing, such as the Andersen and the Marple-Miller, but are hindered by the absence of a published acceptable range for the distance to the impaction collection surface and by the limited published information on the shape of their stage collection efficiency curves. 相似文献
6.
For the purpose of modeling indoor particle dispersion with an Eulerian drift flux model or analyzing indoor particle deposition onto various surfaces accurately, it may take considerable time to calculate the deposition velocity for each surface as numerical integration or calculation is usually needed. In this article, a modified three-layer model is presented to calculate indoor particle deposition velocities for surfaces with different inclinations and for different friction velocities. Then, 1020 cases, covering the common indoor scenarios, were modeled to obtain a database of indoor particle deposition velocities. Based on the results of the 1020 cases, an empirical equation was generated to determine indoor particle deposition velocities. The empirical equation was divided into four parts, named the Fine zone, Coarse zone, Zero zone, and Transition zone. In the Fine zone, the friction velocity decides the particle deposition velocity, while in the Coarse zone, the inclination angle of the surface is the decisive parameter for the deposition velocity. The results show that the average error of the empirical equation to the database was 1.53%, 1.50%, and 21.93% in the Fine zone, Coarse zone, and Transition zone, respectively. The deposition velocities in the Zero zone can all be deemed as zero. Empirical equation predictions agree well with experimental data for a spherical chamber (Cheng 1997). The empirical equation generated in this study is therefore applicable for easily calculating the boundary conditions for Eulerian drift flux model or analyzing indoor particle deposition onto smooth surfaces with varying inclinations with reasonable accuracy. Copyright 2012 American Association for Aerosol Research 相似文献
7.
Atmospheric aerosols are one of the least understood components of the climate system and incur adverse health effects on susceptible populations. Organic aerosols can make up as much as 80% of atmospheric aerosols (Lim and Turpin 2002), and so its quantification and characterization plays an important role in reducing our uncertainty with regards to aerosol impacts on health and climate. As the number of organic molecules in the atmosphere are diverse in number (Hamilton et al. 2004), we advance a functional group representation of organic molecules as measured by Fourier transform infrared spectroscopy (FTIR) to characterize the chemical composition of particle samples. This study describes and evaluates the algorithm introduced by Russell et al. (2009) for apportionment and quantification of oxygenated (carbonyl and hydroxyl) functional groups from infrared absorption spectra. Molar absorptivities for carbonyl and hydroxyl bonds in carboxylic groups are obtained for several dicarboxylic compounds, and applied to a multifunctional compound and mixture to demonstrate the applicability of this method for more complex samples. Furthermore, functional group abundances of two aldehydic compounds, 2-deoxy-d-ribose and glyceraldehyde, atomized from aqueous solution are in quantitative agreement with number of bonds predicted after transformation of these compounds into diols. The procedure for spectra interpretation and quantitative analysis is described through the context of an algorithm in which contributions of background and analyte absorption to the infrared spectrum are apportioned by the superposition of lineshapes constrained by laboratory measurements. Copyright 2013 American Association for Aerosol Research 相似文献
8.
Particle deposition in the human mouth-throat is an important factor in evaluating efficiency of drug delivered by inhalation devices, such as pMDIs or DPIs. Current USP standard impactor induction ports (which serve as an in vitro representative of the adult mouth-throat) underpredict in vivo mouth-throat deposition. However, preliminary experimental data in the prototype geometry of a highly idealized mouth-throat has indicated that it is a promising replacement for the USP mouth-throat (Zhang et al. 2004). In this study, partial optimization design of the highly idealized mouth-throat was performed using computational fluid dynamics (CFD) simulations. The performance of six candidate highly idealized mouth-throat geometries, each with a straight tube inlet of inner diameter 17.3 mm, was evaluated experimentally by measuring monodisperse particle deposition efficiency. Gravimetry was used to determine particle deposition in these geometries. Monodisperse particles of di-2-ethylhexyl-sebecate (DEHS) oil with mass median diameters of 2.1–7.5 μm (GSD < 1.1) were used at two steady inhalation flow rates of 30 and 90 l/min. The results showed that, at the higher flow rate of 90 l/min, a mouth-throat with a bend region 8.5 mm in diameter and a curvature radius of 50 mm follows the in vivo average summarized by Stahlhofen et al. (1989) most closely. In contrast, at the lower flow rate of 30 l/min, the mouth-throat with a bend region 7.5 mm in diameter mimics the above in vivo curve but the in vivo-in vitro match is worse than for 90 l/min case. Enhanced particle deposition caused by a Reynolds number effect was observed in all geometries studied. Overall, an adequately designed highly idealized mouth-throat can largely reproduce in vivo mouth-throat deposition. For different flow rates, different key dimensions are required with the present highly idealized mouth-throats in order to adequately reproduce the in vivo average curve. 相似文献
9.
10.
《Journal of Sulfur Chemistry》2013,34(4-5):381-391
Pyridine-2(1H)-thione 1 reacted with phenyl isothiocyanate to give pyrido[2,3-d]pyrimidine derivative 3. Compound 3 reacted with halogen containing compounds 4a–d and methyl iodide in dimethylformamide/potassium hydroxide solution at room temperature to give 2,7-bisalkylthiopyrido[2,3-b]pyrimidine derivatives 5a–d and 9, respectively. Compounds 5a–d could be cyclized into thienopyrido[2,3-d]pyrimidine derivatives 6a–d by boiling with ethanolic potassium hydroxide solution. Compound 6a reacted with acetic anhydride or formic acid and gave the corresponding pyrimido[4″,5″:4′,5′]thieno[3′,2′:5,6]pyrido[2,3-d]pyrimidine derivatives 8a,b. Compound 9 reacted with hydrazine hydrate to yield pyrazolo[4′,3′:5,6]pyrido[2,3-d]pyrimidine derivative 11 which could be reacted with nitrous acid and dimethylformamide-dimethylacetal (DMF-DMA) and gave the final isolable products corresponding to the pyrazolo[4′,3′:5,6]pyrido[2,3-d]tetrazolo-[5,1-b]pyrimidine and pyrimido[1″,2″:1′,5′]pyrazolo[4′,3′:5,6]pyrido[2,3-d]1 2 4triazolo-[4,3-b] pyrimidine derivatives 13 and 17, respectively. Compound 11 also reacted with some β-dicarbonyl compounds such as acetylacetone (18) and ethyl acetoacetate (20) to yield the corresponding pyrimido[1″,2″:1′,5′]pyrazolo[4′,3′:5,6]pyrido[2,3-d]pyrimidine derivatives 19 and 21, respectively. Finally, compound 11 reacted with chloroacetyl chloride (22) to give the corresponding imidazo[1″′,2″′:1″,5″]pyrazolo[4″,3″:5′,6′]pyrido[3′,2′:5,6]pyrimido[2,1-c]1 2 4triazine derivative 23. 相似文献
11.
This paper describes the usefulness of one-dimensional diffusion-ordered NMR spectroscopy (1D-DOSY) in investigating dynamics and interactions of molecules in solution as well as in analyzing the structure of molecules. We synthesized the three imines, N-benzylidene-4-methylbenzene-Sulfonamide (1), N-(4-chloro-benzylidene)4-methyl-benzene-sulfonamide (2), and N- (4-methoxybenzylidene)-4-methyl-benzene sulfonamide (3), and acetophenone (4) and its three derivatives, 4-chloroacetophenone (5), 4-nitro-acetophenone (6), and 4-methoxyaceto -phenone (7). 1D-DOSY was applied to a mixture of compounds (1), (2), and (3) and to a mixture of compounds (4), (5), (6), and (7). Although 1 H NMR chemical shifts of the molecules in the mixtures resembled one another in the surrounding, we could distinguish signals of the individual molecules in each mixture on the basis of the NMR data and the values of the diffusion coefficient. Also, we could found the correlation of the measured diffusion coefficients and the calculated molecular volumes. 相似文献
12.
Laboratory experiments of bubble bursting have shown that particle production increases with concentration for aqueous solutions of NaCl (Spiel 1998). Here, experiments with a submicron Na particle counter for three Na salts—NaCl, NaBr, and NaI—show comparable trends. Similarities in behavior are evident when the concentration for each salt is normalized to a threshold concentration (Lessard and Zieminski 1971). The number, size, and mass of particles produced increase with normalized solution concentration, suggesting that the same transition that controls ionic entropy and self-diffusion in aqueous solutions will govern the bubble bursting process. Further insight into the controlling forces is provided by the prediction of the number, size, and mass of particles produced from the Eotvos number, the ratio of buoyant to surface forces of the aqueous solution. The similarities among the parameterizations of particle properties to the Eotvos number for all three Na salts provide a strong indication that, for similar density solutions, particle production is dominated by surface forces, independent of chemical compositions. A complete mechanistic interpretation of particle production is limited by our inability to capture (theoretically or experimentally) both the macroscopic fluid mechanics of film rupture and the microscopic intermolecular interactions of strong ionic solutions. However, the parameterizations to dimensionless quantities of aqueous solutions presented here are sufficient to predict the essential characteristics of particle production. The collapse of the experimental results to common curves for several different salts shows the predictive ability of these parameterizations for other mixtures. 相似文献
13.
The numerical models for predicting the collection efficiency of particles in the size range of 0.3 ～ 10.0 μm in electrostatic precipitators (ESPs) have been well developed. However, for nanoparticles, or particles with the diameter below 100 nm, the existing models can't predict the collection efficiency very well because the electric field and ion concentration distribution were not simulated, or charging models were not adopted appropriately to calculate particle charges. In this study, a 2-D numerical model was developed to predict the nanoparticle collection efficiency in single-stage wire-in-plate ESPs. Laminar flow field was solved by using the Semi-Implicit Method for Pressure-Linked Equation (SIMPLER Method), while electric field strength and ion concentration distribution were solved based on Poisson and diffusion-convection equations, respectively. The charged particle concentration distribution and the particle collection efficiency were then calculated based on the convection-diffusion equation with particle charging calculated by Fuchs diffusion charging theory. The simulated collection efficiencies of 6–100 nm nanoparticles were compared with the experimental data of Huang and Chen (2002) for a wire-in-plate dry ESP (aerosol flow rate: 100 L/min, applied voltage: ?15.5 ～ –21.5 kV). Good agreement was obtained. The simulated particle collection efficiencies were further shown to agree with the experimental data obtained in the study for a wire-in-plate wet ESP (Lin et al. 2010) (aerosol flow rate: 5 L/min, applied voltage: +3.6 ～+4.3 kV) using monodisperse NaCl particles of 10 and 50 nm in diameter. It is expected that the present model can be used to facilitate the design of ESPs for nanoparticle control and electrostatic nanoparticle samplers. 相似文献
14.
J. A. Hubbard J. E. Brockmann J. Dellinger D. A. Lucero A. L. Sanchez B. L. Servantes 《Aerosol science and technology》2013,47(2):138-147
Fibrous filter pressure drop and aerosol collection efficiency were measured at low air pressures (0.2–0.8 atm) and high face velocities (5–19 m/s) to give fiber Reynolds numbers lying in the viscous-inertial transition flow regime (1–15). In this regime, contemporary filtration theory based on Kuwabara's viscous flow through an ensemble of fibers underpredicts single fiber impaction by several orders of magnitude. Streamline curvature increases substantially as air stream inertial forces become significant. Dimensionless pressure drop measurements followed the viscous-inertial theory of Robinson and Franklin (1972) rather than Darcy's linear pressure–velocity relationship. Sodium chloride and iron nano-agglomerate aerosols were tested to provide a comparison between particles of dissimilar densities and shape factors. Total filter efficiency collapsed when plotted against the particle Stokes number and fiber Reynolds number. Efficiencies were then modeled with an impactor type equation where the cutpoint Stokes number and a steepness parameter described data well in the sharply increasing portion of the curve (20%–80% efficiency). A minimum in collection efficiency was observed at small Stokes numbers and attributed to interception and diffusive effects. The cutpoint Stokes number was a linearly decreasing function of fiber Reynolds number. Single fiber efficiencies were calculated from total filter efficiencies and compared to contemporary viscous flow impaction theory (Stechkina et al. 1969), and numerical simulations of single fiber efficiencies from the literature. Existing theories underpredicted measured single fiber efficiencies, although comparison is problematic. The assumption of uniform flow conditions for each successive layer of fibers is questionable; thus, the common exponential relationship between single fiber efficiency and total filter efficiency may not be appropriate in this regime. Copyright 2012 American Association for Aerosol Research 相似文献
15.
Zhi Ning Katharine F. Moore Andrea Polidori Constantinos Sioutas 《Aerosol science and technology》2013,47(12):1098-1110
Recently a new compact aerosol concentration enrichment system was developed at the University of Southern California, specifically intended to provide particle-laden air at flow rates and pressures suitable for interfacing with on-line continuous aerosol instrumentation for chemical analysis such as mass spectrometers. The re-design and engineering of the miniature Versatile Aerosol Concentration Enrichment System (mVACES) and primarily laboratory-based validation of the individual components and overall system has been previously reported (Geller et al. 2005). From September to December 2005, a field performance validation study of the mVACES was conducted in Los Angeles, California at a mixed urban site influenced by both freeway traffic and construction. A variety of continuous and semi-continuous physical and chemical composition measurements were performed to assess the performance of the mVACES compared to accepted methods for validation. Near-ideal performance for aerosol concentration enhancement by the mVACES was observed for mass and number distribution with minimal evidence for distortion of the size distribution. Similarly, near-ideal concentration enhancement factors were observed for both inorganic and organic species suggesting that the mVACES works equally well across the range of externally mixed urban aerosol. The data suggest that aerosol concentration enhancements up to an ideal factor of 20 in a delivered flow on the order of 1.5 liters min–1 are readily achievable in an urban environment for the ambient conditions studied. 相似文献
16.
The hypothesis that hydroxylation of the 7-methyl group is the first step in metabolic activation of 7,12-dimethylbenz[a]anthracene (DMBA) was advanced over three decades ago (1, 2). A considerable body of evidence supports the hypothesis (3). A chemical model for the oxidative metabolism of DMBA may be useful in understanding the mechanism of metabolic activation of DMBA and other methylated carcinogenic hydrocarbons, particularly the first step. Here we show that a nonenzymatic one-electron oxidation pathway transforms DMBA to carcinogenic alcohol and meso-aldehyde metabolites. The results are consistent with the hypothesis that hydroxylation of the 7-methyl and/or 12-methyl groups is the first metabolic step in DMBA activation. The hypothesis predicts that hydroxylation of other meso-methyl-substituted hydrocarbons is the first essential step in the metabolic activation of methylated carcinogenic hydrocarbons. 相似文献
17.
Abstract We discuss the performance of “closed-end” fluctuation tests, used to detect changes in the structural stability of a model, in the case where the time horizon is large and the observations do not possess high enough moments. It is demonstrated via a simulation study that, in the latter case, the choice of the boundary function should take into account the number of moments existing; otherwise the actual size of the test may exceed the nominal level. We suggest an alternative “open-end” fluctuation procedure and study its asymptotic behavior. It turns out that if an improper boundary function is chosen, then the null hypothesis may be rejected even if it is true. This means that an appropriate choice of the boundary function requires some prior information about the tail heaviness of the observations. This is different from the cumulative sum-based monitoring schemes suggested by Chu et al. (1996) and further studied by Horváth et al. (2004). 相似文献
18.
Mourad Ben Othmane Michel Havet Evelyne Gehin Camille Solliec 《Aerosol science and technology》2013,47(9):775-784
An improved Eulerian model is proposed to predict particle deposition velocity in a typical mechanical ventilation system of a dairy food factory. For fully developed turbulent flow, the model is modified based on the three-layer model developed by Zhao and Wu (2006a), accounting for thermophoresis as well as turbophoresis, Brownian diffusion, turbulent diffusion, and gravitational settling. Based on in-situ measurements of the aerosol size distributions, particles discussed in this article were in the size range 0.3–20 μm. The measured mass concentration and the predicted particle deposition velocity were used to calculate the deposited particle mass flux in the ventilation duct. The results indicate that the effects of temperature gradients and of surface roughness should be considered in food factories ventilation ducts. For horizontal surfaces, it is shown that even a little difference between empirical and theoretical models can lead to a 2-fold difference in the predicted deposited particle mass flux. Findings of this work may help to identify the specific parameters for cleaning procedures. 相似文献
19.
Dong Keun Song Hyuksang Chang Sang Soo Kim Kikuo Okuyama 《Aerosol science and technology》2013,47(8):701-712
The effect of Brownian diffusive particle trajectory of nanoparticles on the transfer function of the low pressure Differential Mobility Analyzer (LPDMA) was evaluated by a numerical simulation of the Langevin dynamic equation. The results of the simulation were compared with previously reported experimental results (Seto et al. 1997; Seol et al. 2000) and Stolzenburg's transfer function (1988). As the operational pressure decreased, the peak and FWHM (full width of the transfer function at half of its maximum) values of transfer function, as calculated by numerical simulation, were increased, which was not evident from Stolzenburg's transfer function. In comparison with the experiments of Seto et al., discrepancies in the higher electrical mobility regime than from central mobility were found, which could be caused by the incomplete flow control of their LPDMA. However, the transfer function, as calculated by numerical simulation was in good agreement with experimental results reported by Seol et al., performed with the improved LPDMA at well-controlled operation conditions. 相似文献
20.
A variant of the Vienna DMA (Winklmayr et al. 1991; Reischl et al. 1997) with inner and outer electrode radii of 25 and 33 mm, and a conventional trumpet inlet diameter of 97 mm has been tested. It incorporates a reduced pressure drop sheath gas exhaust system that enables reaching flow rates approaching 4000 L/min. Several new additional flow features are included to delay the transition to turbulent conditions. A cylindrical geometry with a DMA length L of 97 mm (distance between the aerosol inlet and outlet slits) is seen to keep the flow laminar up to the highest Reynolds number achieved, though showing slight signs of flow quality deterioration at about Re = 20,000. An equally long DMA with an inner electrode shaped as a 5° cone caped by a spherical dome remains stable up to the highest Reynolds number achieved. It is expected to continue this trend to considerably higher flow rates. Both these long configurations exhibit line widths close to the ideal Brownian diffusion limit, reaching FWHH of 4% for a particle mass diameter of 1 nm. A short DMA with an axial length L of 18 mm and an inner electrode shaped as a 5° cone caped by an ellipse of 3/2 aspect ratio remains also laminar at the highest speeds attained, and exhibits FWHH as small as 2.4%. It departs moderately from ideal behaviour at small flow rates, presumably due to its non-cylindrical geometry. More serious departures observed at high Reynolds numbers may perhaps be due to flow unsteadiness radiated into the working section by sound waves from the turbulent exhaust region. This is the first report of a DMA capable of excellent resolution at 1 nm, yet with a sufficiently wide and long working section to enable (in principle) covering the size range up to 100 nm. 相似文献