Browsing by Subject "Aerosol"
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Item A two-stage 100 l/min circumferential slot virtual impactor system for bioaerosol concentration(2009-05-15) LaCroix, Daniel EdwardA two -stage circumferential slot virtual impactor aerosol concentrator system has been developed that is designed for nominal operational conditions of a 2 ?m AD cutpoint, an aerosol inflow to the first stage of 100 L/min and a minor flow rate from the second stage of 1 L/min. Each unit was tested separately before being combined in the system. However, because of high inter-stage losses, a sheath air system was inserted between the two stages, wherein a small amount of air was injected into the apex of a cone placed on top of the second stage. The sheath air displaced the stagnation point at the apex of the cone and redirected particles into the sampling zone of the second stage unit. The cutpoint particle size of the system was 2.5 ?m AD at the nominal flow rate. The dynamic range (ratio of upper limit to the lower limit of aerodynamic particle diameter associated with transmission efficiencies of 50%) was 5.4, and the largest particle size for which the transmission was at least 50% is 13.6 ?m AD. When run at 67 L/min, the cutpoint is 4 ?m AD and the dynamic range is 3.75; at 150 L/min the cutpoint is 2.05 ?m AD and the dynamic range is not less than 4.74. The pressure drop across the system is 685 Pa (2.75 in. H2O). This yields an ideal power consumption of 0.77 watts.Item Ambient aerosol sampling inlet for flow rates of 100 and 400 l/min(2009-05-15) Baehl, Michael MatthewNew bioaerosol sampling inlets were designed and tested that have nominal exhaust flow rates of 100 L/min to 400 L/min, and which have internal fractionators and screens to scalp large, unwanted particles and debris from the transmitted size distribution. These units consist of the same aspiration section, which is a 100 L/min Bell Shaped Inlet (BSI-100), and different pre-separators. The pre-separators are called the IRI-100 (Inline Real Impactor) with an exhaust flow rate of 100 L/min, the IRI-400 (exhaust flow rate of 400 L/min), the IVI-300 (Inline Virtual Impactor for a flow rate of 300 L/min) and the IVI-400. These units were tested in a wind tunnel at speeds of 2, 8, and 24 km/hr with particle sizes between 3 and 20 ?m AD (aerodynamic diameter). The units show wind independent characteristics over the range of wind speeds tested. The aspiration section of the BSI-100 has greater than 85% penetration for particle sizes ? 10 ?m AD. The IRI-100, IRI-400, IVI-300 and IVI-400, when combined with the BSI-100 all provide cutpoints of 11 ? 0.5 ?m AD.Item Application of computational fluid dynamics to aerosol sampling and concentration(2009-05-15) Hu, ShishanAn understanding of gas-liquid two-phase interactions, aerosol particle deposition, and heat transfer is needed. Computational Fluid Dynamics (CFD) is becoming a powerful tool to predict aerosol behavior for related design work. In this study, FLUENT 6 is used to analyze the performance of aerosol sampling and concentration devices including inlet components (impactors), cyclones, and virtual impactors. The ? ? k model was used to predict particle behavior in Inline Cone Impactor (ICI) and Jet-in-Well impactor (JIW). Simulation provided excellent agreement with experimental test results for a compact ICI. In the JIW, compound impaction is shown to cause the device to have a smaller cutpoint Stokes number than the single impaction unit. The size ratio of the well-to-jet was analyzed to find its influence on the total and side collections. Simulation is used to analyze liquid film, flow structure, particle collection, pressure drop, and heating requirements for a bioaerosol sampling cyclone. A volume of fluid model is used to predict water film in an earlier cyclone. A shell-volume is developed to simulate thin liquid film in large device. For the upgraded version cyclone, simulation is verified to successfully predict cutpoint and pressure drop. A narrowing-jet is shown to describe the flow evolution inside the axial flow cyclone. Turbulent heat transfer coefficients and surface temperatures are analyzed and heaters are designed for this cyclone. A double-outlet cyclone was designed and its pressure drop decreased about 25%, compared with a single-outlet cyclone. A scaled-down 100 L/min cyclone was also designed and tested based on the 1250 L/min unit. CFD is used to design a Circumferential Slot Virtual Impactor (CSVI) which is used for concentration of bioaerosol particles. Simulations showed a 3-D unstable flow inside an earlier version CSVI, which could explain acoustic noise and particle loss observed in the experiment. A smaller CSVI unit was designed using simulation and its flow was shown to be stable. CFD was then used to analyze the wake flow downstream of the posts to reduce particle losses and eliminate flow instabilities caused by wakes. A successful solution, moving the posts outside was developed by the use of CFD.Item Computational Fluid Dynamics Study of Aerosol Transport and Deposition Mechanisms(2012-07-16) Tang, YingjieIn this work, various aerosol particle transport and deposition mechanisms were studied through the computational fluid dynamics (CFD) modeling, including inertial impaction, gravitational effect, lift force, interception, and turbophoresis, within different practical applications including aerosol sampling inlet, filtration system and turbulent pipe flows. The objective of the research is to obtain a better understanding of the mechanisms that affect aerosol particle transport and deposition, and to determine the feasibility and accuracy of using commercial CFD tools in predicting performance of aerosol sampling devices. Flow field simulation was carried out first, and then followed by Lagrangian particle tracking to obtain the aerosol transport and deposition information. The CFD-based results were validated with experimental data and empirical correlations. In the simulation of the aerosol inlet, CFD-based penetration was in excellent agreement with experimental results, and the most significant regional particle deposition occurred due to inertial separation. At higher free wind speeds gravity had less effect on particle deposition. An empirical equation for efficiency prediction was developed considering inertial and gravitational effects, which will be useful for directing design of similar aerosol inlets. In the simulation of aerosol deposition on a screen, a "virtual surface" approach, which eliminates the need for the often-ambiguous user defined functions, was developed to account for particle deposition due to interception. The CFD-based results had a good agreement compared with experimental results, and also with published empirical correlations for interception. In the simulation of turbulent deposition in pipe flows, the relation between particle deposition velocity and wall-normal turbulent velocity fluctuation was quantitative determined for the first time, which could be used to quantify turbulent deposition, without having to carry out Lagrangian particle tracking. It suggested that the Reynolds stress model and large eddy simulation would lead to the most accurate simulated aerosol deposition velocity. The prerequisites were that the wall-adjacent y+ value was sufficiently low, and that sufficient number of prism layers was applied in the near-wall region. The "velocity fluctuation convergence" would be useful criterion for judging the adequacy of a CFD simulation for turbulent deposition.Item Direct numerical simulation of particle-laden turbulence in a straight square duct(Texas A&M University, 2004-09-30) Sharma, GauravParticle-laden turbulent flow through a straight square duct at Re? = 300 is studied using direct numerical simulation (DNS) and Lagrangian particle tracking. A parallelized 3-D particle tracking direct numerical simulation code has been developed to perform the large-scale turbulent particle transport computations reported in this thesis. The DNS code is validated after demonstrating good agreement with the published DNS results for the same flow and Reynolds number. Lagrangian particle transport computations are carried out using a large ensemble of passive tracers and finite-inertia particles and the assumption of one-way fluid-particle coupling. Using four different types of initial particle distributions, Lagrangian particle dispersion, concentration and deposition are studied in the turbulent straight square duct. Particles are released in a uniform distribution on a cross-sectional plane at the duct inlet, released as particle pairs in the core region of the duct, distributed randomly in the domain or distributed uniformly in planes at certain heights above the walls. One- and two-particle dispersion statistics are computed and discussed for the low Reynolds number inhomogeneous turbulence present in a straight square duct. New detailed statistics on particle number concentration and deposition are also obtained and discussed.Item An evaluation of the use of superparamagnetic iron oxide nanoparticles to overcome extracellular barriers to lung disease for drug delivery(2011-12) McGill, Shayna Lorraine; Smyth, Hugh; Croyle, Maria; McConville, Jason; Wiederhold, Nathan; Roy, KrishnenduPrimary barriers to drug delivery include mucus and biofilms, which can hinder drug and gene delivery by several orders of magnitude, preventing effective therapeutic effects. By understanding the physical and chemical properties of these ubiquitous barriers, one may employ drug delivery approaches, such as design of nanoparticle and microparticle systems, to attempt to overcome the transport barriers. Nanoparticles are a growing interest in drug delivery, specifically as drug carriers, though most will become entrapped within these extracellular barriers further limiting their desired affects. Previous studies have generally manipulated the surface chemistries or size of these nanoparticles to allow for nearly a 2-fold increase in passive diffusion through barriers. To expand the current ideas of overcoming these barriers, studies in presented in this dissertation were performed using a type of active nanoparticle, superparamagnetic iron oxide nanoparticles. It was first investigated whether these particles would disrupt extracellular barriers under an oscillating magnetic field, which resulted in a 2-fold increased diffusion of particles upon biopolymer breakage. Secondly, influences of an external static magnetic field on diffusion of these nanoparticles through model barriers were determined. Both of these methods resulted in higher fold increases, reaching up to 28-fold compared to 2-fold as described in the literature. Next an examination of drug permeation enhancement in models of extracellular barriers by nanoparticle interactions was performed, using a passive mechanism as found in the literature. With a range of different nanoparticles including diesel particulate matter, barrier function was disrupted resulting in a 5-fold increase in drug permeation. To further manipulate drug diffusion an assisted delivery systems was observed, where magnetic nanoparticles could influence un-associated drug diffusion, resulting in 4-fold increase in drug diffusion. Finally formulations of nanosuspensions were created for aerosol delivery and their performance evaluated in vitro. A dry powder formulation containing drug and nanoparticles was formulated using a spray-drying technique. Upon barrier deposition studies using the dry powder formulation, permeation rates were determined resulting in a 2-fold increase for nanoparticle permeation. When drug diffusion was determined up to a 54-fold increase in drug was seen when co-delivered with nanoparticles, compared to controls containing only drug.Item Flammability and Combustion Behaviors in Aerosols Formed by Industrial Heat Transfer Fluids Produced by the Electrospray Method(2012-10-19) Lian, PengThe existence of flammable aerosols presents a high potential for fire hazards in the process industry. Various industrial fluids, most of which operate at elevated temperatures and pressures, can be atomized when released under high pressure through a small orifice. Because of the complexity in the process of aerosol formation and combustion, the availability of data on aerosol flammability and flame propagation behaviors is still quite limited, making it difficult to evaluate the potential fire and explosion risks from released aerosols in the process industry and develop safety measures for preventing and/or mitigating aerosol hazards. A study is needed to investigate the relationship between aerosol combustion behaviors and the properties of the aerosols. This dissertation presents research on the combustion behaviors of flammable aerosols. Monodisperse aerosols created by industrial heat transfer fluids were generated using electrospray. The characteristics of flame propagations in aerosols and the influence of the presence of fuel droplets in the system are studied in the aerosol ignition tests. Flames in aerosols are characterized by non-uniform shapes and discrete flame fronts. Flames were observed in different burning modes. Droplet evaporation was found to play an important role in aerosol burning modes. Droplet evaporation behaviors and fuel vapor distributions are further related to aerosol droplet size, droplet spacing, movement velocity, and liquid volatility. The burning mode of a global flame with rapid size expansion is considered the most hazardous aerosol combustion scenario. This burning mode requires a smaller droplet size and smaller space between droplets. Larger droplet sizes and spacing may hinder the appearance of global flames. But when the liquid fuel has a certain level of volatility, there is an uneven distribution of fuel vapor in the system and this may cause the unique phenomenon of burning mode variations combined with enhanced flame propagation speed. Using an integrated model, the minimum ignition energy values of aerosols were predicted. The aerosol minimum ignition energy is influenced by the fuel-air equivalence ratio and the droplet size. Higher equivalence ratios, up to 1.0, significantly reduce the minimum ignition energy, while larger droplet sizes result in a higher minimum ignition energy.Item Investigation of the optical properties of secondary organic aerosols generated from hydrocarbon ozonolysis(2011-05) Redmond, Haley E.; Thompson, Jonathan E.; Pappas, DimitriThis thesis describes and evaluates a simple scheme by which the refractive index (at 589 nm) of non-absorbing components common to secondary organic aerosols (SOA) may be predicted from molecular formula and density (g / cm3). The QSPR approach described is based on three parameters linked to refractive index – molecular polarizability, the ratio of mass density to molecular weight, and degree of unsaturation. After computing these quantities for a training set of 111 compounds common to atmospheric aerosols, multi-linear regression analysis was conducted to establish a quantitative relationship between the parameters and accepted value of refractive index. The resulting quantitative relationship can often estimate refractive index to ± 0.01 when averaged across a variety of compound classes. A notable exception is for alcohols for which the model consistently underestimates refractive index. Homogenous internal mixtures can conceivably be addressed through use of either the volume or mole fraction mixing rules commonly used in the aerosol community. Predicted refractive indices reconstructed from composition data presented in the literature generally agree with previous reports of SOA refractive index. Additionally, the predicted refractive indices lie near measured values we report for SOA generated from vapors of α-pinene and toluene provided the concentration of the precursor hydrocarbon is low. This method may find use in reconstructing optical scattering of organic aerosols if mass composition data is known. Alternatively, the method described could be incorporated into in models of organic aerosol formation / phase partitioning to better constrain organic aerosol optical properties.Item Light Scattering Problem and its Application in Atmospheric Science(2011-02-22) Meng, ZhaokaiThe light scattering problem and its application in atmospheric science is studied in this thesis. In the first part of this thesis, light scattering theory of single irregular particles is investigated. We first introduce the basic concepts of the light scattering problem. T-matrix ansatz, as well as the null-field technique, are introduced in the following sections. Three geometries, including sphere, cylinder and hexagonal column, are defined subsequently. Corresponding light scattering properties (i.e., T-matrix and Mueller Matrix) of those models with arbitrary sizes are simulated via the T-matrix method. In order to improve the efficiency for the algorithms of single-light scattering, we present a user-friendly database software package of the single-scattering properties of individual dust-like aerosol particles. The second part of this thesis describes this database in detail. Its application to radiative transfer calculations in a spectral region from ultraviolet (UV) to far-infrared (far-IR) is introduced as well. To expand the degree of morphological freedom of the commonly used spheroidal and spherical models, triaxial ellipsoids were assumed to be the overall shape of dust-like aerosol particles. The software package allows for the derivation of the bulk optical properties for a given distribution of particle microphysical parameters (i.e., refractive index, size parameter and two aspect ratios). The array-oriented single-scattering property data sets are stored in the NetCDF format. The third part of this thesis examines the applicability of the tri-axial ellipsoidal dust model. In this part, the newly built database is equipped in the study. The precomputed optical properties of tri-axial models are imported to a polarized addingdoubling radiative transfer (RT) model. The radiative transfer property of a well-defined atmosphere layer is consequently simulated. Furthermore, several trial retrieval procedures are taken based on a combination of intensity and polarization in the results of RT simulation. The retrieval results show a high precision and indicate a further application in realistic studies.Item Observations of Secondary Organic Aerosol Production and Soot Aging under Atmospheric Conditions Using a Novel Environmental Aerosol Chamber(2012-02-14) Glen, CrystalSecondary organic aerosols (SOA) comprise a substantial fraction of the total global aerosol budget. While laboratory studies involving smog chambers have advanced our understanding of the formation mechanisms responsible for SOA, our knowledge of the processes leading to SOA production under ambient gaseous and particulate concentrations as well as the impact these aerosol types have on climate is poorly understood. Although the majority of atmospheric aerosols scatter radiation either directly or indirectly by serving as cloud condensation nuclei, soot is thought to have a significant warming effect through absorption. Like inorganic salts, soot may undergo atmospheric transformation through the vapor condensation of non-volatile gaseous species which will alter both its chemical and physical properties. Typical smog chamber studies investigating the formation and growth of SOA as well as the soot aging process are temporally limited by the initial gaseous concentrations injected into the chamber environment. Furthermore, data interpretation from such experiments is generally restricted to the singular gaseous species under investigation. This dissertation discusses the use of a new aerosol chamber designed to study the formation and growth of SOA and soot aging under atmospherically relevant conditions. The Ambient Aerosol Chamber for Evolution Studies (AACES) was deployed at three field sites where size and hygroscopic growth factor (HGF) of ammonium sulfate seed particles was monitored over time to examine the formation and growth of SOA. Similar studies investigating the soot aging process were also conducted in Houston, TX. It is shown that during the ambient growth of ammonium sulfate seed particles, as particle size increases, hygroscopic growth factors decrease considerably resulting in a significant organic mass fraction in the particle phase concluding an experiment. Observations of soot aging show an increase in measured size, HGF, mass and single scattering albedo. Ambient growth rate comparisons with chamber growth yielded similar trends verifying the use of AACES to study aerosol aging. Based on the results from this study, it is recommended that AACES be employed in future studies involving the production and growth of SOA and soot aging under ambient conditions in order to bridge the gaps in our current scientific knowledge.Item Oxide-metal nanoparticles using laser ablation of microparticle aerosols(2009-08) Nahar, Manuj; Kovar, Desiderio; Becker, Miachel F.We have studied a continuous aerosol process for producing oxide nanoparticles with sizes of 10-60 nm that are decorated with smaller 1-3 nm metallic nanoparticles. Such particles may be useful in a number of areas including catalysis and as contrast enhancement agents in biomarkers. To produce the oxide nanoparticle carriers, an aerosol of 1-10 [micrometer] oxide particles are ablated using an excimer laser. The resulting oxide nanoparticle aerosol is then mixed with 1-2 [micrometer] metallic particles and this mixed aerosol is ablated a second time. The oxide nanoparticles are too small to ablate but act as seeds for the nucleation of metallic nanoparticles on the surface of the oxide. The nanoparticle sizes can be varied by changing the gas type or gas pressure in the aerosol. We demonstrate the feasibility of such an approach using two oxides, SiO₂ and TiO₂, and two metals, Au and Ag.Item Study of formation and convective transport of aerosols using optical diagnostic technique(Texas A&M University, 2004-09-30) Kim, Tae-KyunThe characteristics of liquid and solid aerosols have been intensively investigated by means of optical diagnostic techniques. Part I describes the characteristics of liquid aerosol formation formed by heat transfer fluids (HTFs) from bulk liquids. Part II investigates the characteristics of convective transport behavior of solid particles in virtual impactor (VI). The objective of part I is to establish correlations which offer predictions on atomized particle size of HTFs which are widely and commonly used in process industries. There are numerous reports stating that mist explosions formed from leakage cause disastrous accidents in process industries. For safety concerns, the characteristics of mist formation should be known in order to prevent HTFs from catching on fire or exploding. The empirical data on formation of mist are collected by the optical measurement technique, the Fraunhofer diffraction. The Buckingham-PI theorem is applied to establish a correlation between empirical data and representative physical properties of HTFs. Final results of correlations are solved by a statistical method of linear regression. The objective of part II is to investigate the characteristics of convective transport behavior in virtual impactor (VI) which is used to sort polydisperse precursor powder in the process industries of superconductor wire. VI is the device to separate polydisperse particles as a function of particle size by using the difference in inertia between different sizes of particles. To optimize VI performance, the characteristics of convective transport should be identified. This objective is achieved by visualization techniques. The applied visualization techniques are Mie-scattering and laser induced fluorescence (LIF). To investigate analytically, a local Stokes number is introduced in order to offer criteria on predicting the efficiency of VI performance and boundary effect on particle separation. The achieved results can enhance performance and eliminate defects by having knowledge of the behavior of solid particles in VI.Item The application of size- resolved hygroscopicity measurements to understand the physical and chemical properties of ambient aerosol(Texas A&M University, 2005-08-29) Santarpia, Joshua LeeDuring the summer of 2002, a modified tandem differential mobility analyzer (TDMA) was used to examine the size-resolved hydration state of the ambient aerosol in Southeast Texas. Although there were slight variations in the measured properties over the course of the study, the deliquescent particles observed were almost always present as metastable aqueous solutions. A relative humidity (RH) scanning TDMA system was used to measure the deliquescence/crystallization properties of ambient aerosol populations in the same region. During August, sampling was conducted at a rural site in College Station, and in September at an urban site near the Houston ship channel. Measurements from both sites indicate cyclical changes in the composition of the soluble fraction of the aerosol, which are not strongly linked to the local aerosol source. The observations show that as temperature increases and RH decreases, the hysteresis loop describing the RH-dependence of aerosol hygroscopic growth collapses. It is proposed that this collapse is due to a decrease in the ammonium to sulfate ratio in the aerosol particles, which coincides with increasing temperature and decreasing RH. This cyclical change in aerosol acidity may influence secondary organic aerosol (SOA) production and may exaggerate the impact of the aerosol on human health. The compositional changes also result in a daily cycle in crystallization RH that is in phase with that of the ambient RH, which reduces the probability that hygroscopic particles will crystallize in the afternoon when the ambient RH is a minimum. During June and July of 2004 airborne measurements of size-resolved aerosol hygroscopic properties were made near Monterey, California. These were used to examine the change in soluble mass after the aerosol had been processed by cloud. The calculated change in soluble mass after cloud-processing ranged from 0.66 g m-3 to 1.40 g m-3. Model calculations showed these values to be within the theoretical bounds for the aerosols measured. Mass light-scattering efficiencies were calculated from both an averaged aerosol size distribution and from distributions modified to reflect the effects of cloud. These calculations show that the increase in mass light-scattering efficiency should be between 6% and 14%.Item The Evolution of the Physicochemical Properties of Aerosols in the Atmosphere(2011-02-22) Tomlinson, JasonA Differential Mobility Analyzer/Tandem Differential Mobility Analyzer (DMA/TDMA) system was used to measure simultaneously the size distribution and hygroscopicity of the ambient aerosol population. The system was operated aboard the National Center for Atmospheric Research/National Science Foundation (NCAR/NSF) C-130 during the 2006 Megacity Initiative: Local and Global Research Observations (MILAGRO) field campaign followed by the 2006 Intercontinental Chemical Transport Experiment ? Phase B (INTEX-B) field campaign. The research flights for the MILAGRO campaign were conducted within the Mexico City basin and the region to the northeast within the pollution plume. The aerosol within the basin is dominated by organics with an average measured kappa value of 0.21 /- 0.18, 0.13 /- 0.09, 0.09 /- 0.06, 0.14 /- 0.07, and 0.17 /- 0.04 for dry particle diameters of 0.025, 0.050, 0.100, 0.200, and 0.300 mu m, respectively. As the aerosols are transported away from the Mexico City Basin, secondary organic aerosol formation through oxidation and condensation of sulfate on the aerosols surface rapidly increases the solubility of the aerosol. The most pronounced change occurs for a 0.100 mu m diameter aerosol where, after 6 hours of transport, the average kappa value increased by a factor of 3 to a kappa?of 0.29 /- 0.13. The rapid increase in solubility increases the fraction of the aerosol size distribution that could be activated within a cloud. The research flights for the INTEX-B field campaign investigated the evolution of the physicochemical properties of the Asian aerosol plume after 3 to 7 days of transport. The Asian aerosol within the free troposphere exhibited a bimodal growth distribution roughly 50 percent of the time. The more soluble mode of the growth distribution contributed between 67-80 percent of the overall growth distribution and had an average kappa?between 0.40 and 0.53 for dry particle diameters of 0.025, 0.050, 0.100, and 0.300 mu m. The secondary mode was insoluble with an average kappa?between 0.01 and 0.05 for all dry particle diameters. Cloud condensation nuclei closure was attained at a supersaturation of 0.2 percent for all particles within the free troposphere by either assuming a pure ammonium bisulfate composition or a binary composition of ammonium bisulfate and an insoluble organic.Item The seasonality of aerosol properties in Big Bend National Park(Texas A&M University, 2007-04-25) Allen, Christopher LeeTwo-week sampling periods during the spring, summer, and fall of 2003, and the winter of 2004 were conducted utilizing a tandem differential mobility analyzer (TDMA) and, during the spring and summer, an aerodynamic particle sizer (APS), to characterize the seasonal variability of the Big Bend regions aerosol optical properties. Mass extinction efficiencies and relative humidity scattering enhancement factors were calculated for both externally and internally mixed aerosol populations for all size distributions collected, in an effort to possibly improve upon the default EPA mass extinction efficiencies used for all Class 1 areas across the United States. The mass extinction efficiencies calculated differed to some extent form the default values employed by the EPA. Sulfate, nitrate, and light absorbing carbon (LAC) exhibited a strong dependence on assumed mixing state, while, additionally, sulfate was also dependent on the assumed dominant aerosol. Seasonal variability was seen with all particle types, excluding LAC, with sulfate mass extinction efficiencies displaying the greatest variability with season. Calculated back trajectories indicated that air masses originating from the southeast had elevated mass extinction efficiencies, while, conversely, air masses originating from the southwest and northwest had the smallest mass extinction efficiencies.