Dominant Deposition Mechanism Research Articles

Ensemble of Below-Cloud Scavenging Models for Assessing the Uncertainty Characteristics in Wet Raindrop Deposition Modeling

This work is devoted to the development of an ensemble of below-cloud scavenging models of pollutant aerosol transport into the atmosphere. Among other factors contributing to the uncertainty of the forecasts of the dispersion and deposition of technogenic gas-aerosol releases in the atmosphere, precipitation scavenging is one of the least studied and, in case of precipitation, can be the dominant mechanism for aerosol deposition. To form the ensemble of below-cloud scavenging models, appropriate experimental data, raindrop-aerosol capture models, raindrop terminal velocity parameterizations, and raindrop size distributions were chosen. The pool of models was prepared and then evaluated to adequately describe the experimental data using statistical analysis. Rank diagrams were used to analyze the adequacy of meteorological ensembles; together with the ensemble distribution construction, they allowed selecting the groups of models with such properties as to produce unbiased estimates and dispersion corresponding to the dispersion of the experimental data. The model calculations of the concentration fraction deposited due to below-cloud scavenging were performed using a log-normal distribution with characteristics corresponding to those observed during the accidents at the Chernobyl NPP and Fukushima-1 NPP. The results were compared with those obtained using the models of the NAME and FLEXPART codes. The results of this work can be used to improve the current approaches applied for modelling the distribution of pollutants in the atmosphere in the case of emergency, enhancing the reliability of forecasts by taking into account uncertainties in the results. The formed multi-model ensemble will be included in the decision support system used in responding to releases of radioactive substances into the atmosphere.

Comparison of heating mechanisms of argon helicon plasma in different wave modes with and without blue core

In this work, we investigated the discharge characteristics and heating mechanisms of argon helicon plasma in different wave coupled modes with and without blue core. Spatially resolved spectroscopy and emission intensity of argon atom and ion lines were measured via local optical emission spectroscopy, and electron density was measured experimentally by an RF-compensated Langmuir probe. The relation between the emission intensity and the electron density was obtained and the wavenumbers of helicon and ‘Trivelpiece-Gould’ (TG) waves were calculated by solving the dispersion relation in wave modes. The results show that at least two distinct wave coupled modes appear in argon helicon plasma at increasing RF power, i.e. blue core (or BC) mode with a significant bright core of blue lights and a normal wave (NW) mode without blue core. The emission intensity of atom line 750.5 nm (I ArI750.5nm) is related to the electron density and tends to be saturated in wave coupled modes due to the neutral depletion, while the intensity of ion line 480.6 nm (I ArII480.6nm) is a function of the electron density and temperature, and increases dramatically as the RF power is increased. Theoretical analysis shows that TG waves are strongly damped at the plasma edge in NW and/or BC modes, while helicon waves are the dominant mechanism of power deposition or central heating of electrons in both modes. The formation of BC column mainly depends on the enhanced central electron heating by helicon waves rather than TG waves since the excitation of TG waves would be suppressed in this special anti-resonance region.

Transport and deposition of solid phosphorus-based mineral particles in urine diversion systems

ABSTRACT The deposition of solid phosphorus-based mineral particles is a common problem in urine diversion systems, which occurs in transport systems, particularly in horizontal pipelines. In this work, particle deposition behaviour in turbulent flow in a 3D horizontal pipe was simulated by using the Euler–Lagrange method. The effects of particle diameter, particle density, particle shape factor and fluid flow velocity on particle deposition behaviour were investigated. The results showed that the deposition rate increased by 9.92%,6.88% and 6.88% with increasing particle diameter (10-90 ), particle density (1400 kg/m3–2300 kg/m3), and particle shape factor (0.2–1), respectively. For particles with larger diameters (>90 ) or larger density (>2300 kg/m3), the deposition rate of these particles was almost reached 100%. It was found that gravitational sedimentation was the dominant deposition mechanism in low fluid flow velocity range (0.1–0.5 m/s). As fluid flow velocity increased (>0.5 m/s), turbulent fluctuation became the dominant factor that affected particle motion behaviour, whereas the effect of gravitational sedimentation on particle deposition behaviour declined significantly, and the increase in fluid flow velocity no longer significantly affects deposition rate. It was found that the deposition rate decreased by 29.13% as the fluid flow velocity was increased from 0.1 m/s to 0.5 m/s, while the corresponding deposition rate only decreased by 14.24% when the fluid flow velocity was increased from 0.5 m/s to 2 m/s. The optimal flow velocity was found to range between 0.75 and 1.25 m/s, which may mitigate the deposition of mineral solids in urine diversion systems.

Physical and electrochemical behavior of black nickel coatings in presence of KNO3 and imidazole additives

As a unique type of nickel films, black nickel coatings possess remarkable optical and electrical properties but limited applications owing to their poor structure and corrosion resistance. In this study, black nickel coatings were electrodeposited on St37 steel and optimized utilizing nickel Watts bath modified with potassium nitrate. By investigating the coating structure and current efficiency (CE), optimum bath was determined as 190 g/L NiSO4, 25 g/L NiCl2, 30 g/L H3BO3, and 25 g/L KNO3 which resulted in CE of 79% and a compact structure. Next, cyclic voltammetry and chronoamperometric tests revealed that the dominant deposition mechanism was instantaneous nucleation. Besides studying the changes in CE and cathodic polarization, the improvement of properties with addition of imidazole was investigated by studying the surface morphology, phase structure, light absorption, and corrosion behavior using SEM, XRD, differential reflectance spectroscopy (DRS), potentiodynamic polarization, and electrochemical impedance spectroscopy tests, respectively. Adding imidazole to the deposition bath reduced the grain size and crack width from micro-scale to nano-scale, without affecting its nucleation mechanism or light absorption property. Also, imidazole enhanced the corrosion resistance of the black nickel coatings by 62% reduction of corrosion current density and increasing its polarization resistance by 58%.

Evaluation of pH and deposition mechanisms effect on tin sulfide thin films deposited by chemical bath deposition

Abstract SnS thin films were chemical bath deposited at 65 °C, using pH values from 5.5 to 8.5, for 3 h. X-ray diffraction showed orthorhombic SnS thin films with preferential growth along (111) plane. The morphology of the thin films showed plate-like grains with some agglomerates. X-Ray photoelectron spectroscopy clearly showed peaks corresponding to SnS, additionally were detected small peaks associated to SnS2 and Sn. Furthermore, tin oxides peaks were revealed at higher pH values. The results found for SnS thin films deposited at the different pH values indicated that at the lower pH the dominant deposition mechanisms were ion-by-ion and complex decomposition, while they turn to the hydroxide aggregation mechanism as the pH increased. Finally, a superstrate solar cell (SLG/ITO/ZnO/CdS/SnS/Ag) was made using the SnS thin film deposited at pH = 5.5 as the absorber layer. The J-V characteristics of the solar cell were Voc = 0.104 V, Jsc = 0.160 mA/cm2, FF = 38.48%, and η = 0.013%.

Transport and deposition of ultrafine particles in the upper tracheobronchial tree: a comparative study between approximate and realistic respiratory tract models

This paper presents a computational fluid dynamics (CFD) study of air-particle flows in the upper tracheobronchial tree. Two respiratory tract models, including a parametrically controlled approximate airway model developed by Kitaoka (KG model) and a CT-based patient specific airway (realistic model) were used. Assuming laminar, quasi-steady, three-dimensional air flow and spherical non-interacting ultrafine particles in sequentially bifurcating rigid bronchial airways, airflow patterns and particle transport/deposition in these two airway models were evaluated and compared. Overall deposition efficiency data was compared with the widely adopted ICRP data published by The International Commission on Radiological Protection. Good deposition efficiency agreements were observed between the present respiratory tract models and the ICRP data, which validated the numerical prediction accuracy of the present computational fluid-particle dynamics (CFPD) model. For the two respiratory models, the comparison showed both difference and similarity between the approximate KG model and the realistic model. Specifically, the realistic model showed more complicated airflow patterns due to the increased surface irregularity. The deposition efficiency data revealed a deposition preference in the first-generation airways compared to the rest regions. For ultrafine particles smaller than 10 nm, Brownian diffusion remains the dominant particle deposition mechanism. However, for ultrafine particles with size ranging from 10 nm to 100 nm, the deposition efficiency decreased dramatically with the 100 nm particles approaching to zero deposition in the present bronchial tree scope. The generation-by-generation deposition data presented in this paper is indispensable to the formulation of new lung inhalation exposure models.

Sediment transport mechanisms in altered depositional environments of the Anthropocene Nakdong Estuary: A numerical modeling study

The Nakdong Estuary, Korea, is a dramatic example of an Anthropocene estuary. Over the last century, the construction of two dams has divided the estuary into two discharge energy regimes with the East Nakdong Estuary receiving discharge and the West Nakdong Estuary receiving no discharge. The mean-flow sediment flux gradient during high discharge was the main mechanism for deposition in the East Nakdong Estuary. Because of limited observations, the sediment transport mechanisms for the entire estuary remained unclear. To complement previous observations that were limited to a high discharge event of the East Nakdong Estuary, this study aimed to better understand the spatiotemporal variation of sediment transport and the mechanisms of deposition throughout the Nakdong Estuary. Sediment fluxes and bed level changes were estimated by utilizing the Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST). Results confirmed that the East and West Nakdong Estuaries had different depositional patterns. The East Nakdong Estuary was characterized as a river-dominated environment with a high influence of river discharge that experiences rapid deposition. The West Nakdong Estuary was characterized as an environment mainly influenced by tides and waves that contribute to gradual deposition throughout the year. The mean-flow sediment flux by river discharge was a main mechanism of deposition in the East Nakdong Estuary after the construction of dam. The continuous landward mean-flow flux by tides and waves through the inlets was the dominant mechanism for deposition in the West Nakdong Estuary. These model results suggest that the Nakdong Estuary may serve as an analogue for a microtidal estuary altered by an estuarine dam, particularly those for which there is a monsoonal climate or anthropogenically reduced river discharge.

Dry powder inhaler aerosol deposition in a model of tracheobronchial airways: Validating CFD predictions with in vitro data.

Effective drug delivery into the lungs plays an important role in management of pulmonary diseases that affect millions all around the world. The main objective of this investigation is to study airflow structure, as well as transport and deposition of micron-size particles at different inhalation flow rates in a realistic model of human tracheobronchial airways. The airway model was developed based on computed tomography (CT) images of a healthy 48-years-old female, which includes extrathoracic, trachea, and bronchial airways up to fourth generations. Computational fluid dynamics (CFD) simulations were performed to predict transport and deposition of inhaled particles and the results were compared to our previous in vitro experiments. Airflow structure was studied through velocity contours and streamlines in the extrathoracic region, where the onset of turbulence, reverse flow and subsequently vortex formation, and laryngeal jet are found to be critical phenomenons in the formation of airflow and deposition patterns. The deposition data was presented by deposition efficiency (DE) and deposition fraction (DF) against impaction parameter and Stokes number. At all of the inhalation flow rates, highest values of deposition fractions were devoted to the mouth-throat (MT), tracheobronchial tree (TB), and trachea (Tra), respectively (At 60L/min: MT=6.7%, TB=5.3%, Tra=1.9%). The numerical deposition data showed a good agreement with the experimental deposition data in most of the airway regions (e.g. less than 10% difference between the deposition fractions in the tracheobronchial region). Enhancing inhalation flow rate in all of the airway regions led to an uptrend in deposition rate due to the increase of particles inertia and turbulence level. In addition, the increase of particle deposition with enhancing inhalation flow rate in all of the sections including extrathoracic, trachea, and tracheobronchial tree suggesting that inertial impaction is the dominant deposition mechanism due to the increase of inertial force. In conclusion, the validated CFD model provided an opportunity to cover the limitations of our previous experimental investigation on aerosol deposition of commercial inhalers and became an efficient method for further studies.

Age and genesis of the W-Bi-Cu-F (Au) Nui Phao deposit, Northeast Vietnam: Constrains from U-Pb and Ar-Ar geochronology, fluid inclusions study, S-O isotope systematic and scheelite geochemistry

Northeast Vietnam comprises several tectonic units, which host number of metallic deposits of different types from orogenic gold to intrusion hosted PGE deposits. The Lo Gam domain being part of the NE Vietnam, hosts the Lang Vai gold district, a several Pb–Zn deposits, and the recently discovered super-large W-Bi-Cu-F (Au) Nui Phao deposit. The Nui Phao deposit is 87.9 Mt at 0.19% WO3, 7.95% CaF2, 0.18% Cu, 0.19 g/t Au, and 0.09% Bi, while the measured resource is 25.1 Mt at 0.25% WO3, 8.4% CaF2, 0.23% Cu, 0.26 g/t Au, and 0.108% Bi. The Nui Phao deposit is a very interesting object for research due to location of the orebodies between of two granite massifs of the Cretaceous (Da Lien) and Triassic (Nui Phao) age. Consequently, the temporal and genetic relationships of mineralization with a certain magmatic events are unclear. Here we present mineralogical, compositional, and geochronological data of the Nui Phao deposit in conjunction with physical-chemical researches to understand the ore genesis and its genetic link to a certain magmatic events. According to our observations, at least three different mineral associations are distinguished at the Nui Phao deposit, which include greisens, skarns, and quartz-sulfide ore. Skarn and sulfide ore mineral assemblages generally contain abundant scheelite associated with pyrrhotite, chalcopyrite, and native bismuth. The greisens consist of fluorite, muscovite, and rare molybdenite. The results of fluid inclusions study indicate that at the Nui Phao deposit the initial ore-forming fluid was represented by the reduced (CO2-CH4)–H2O–NaCl(CaCl2) system characterized by high temperatures and moderate salinities. The fluid boiling is the dominant mechanism for ore deposition at the Nui Phao deposit. Relatively homogeneous isotopic compositions of oxygen (δ18OH2O = +6.73 to +9.24‰) and sulfur (δ34S = +1.6 to +3.5‰) that closely correspond to magmatic source, suggest that the ore-forming fluid was generated from cooling granite pluton without contribution meteoric water. The systematic studies of scheelite composition show that ΣREE contents decrease from early to late scheelite generations, which suggest gradual REE depletion of the ore-forming fluid without significant fractionation between LREE, MREE, and HREE. The REEs of scheelite are mainly controlled by the substitution mechanisms Ca2++W6+ ↔ REE3+ + Nb5+ and 3Ca2+ = 2REE3+ + □(Ca). By combining REE features, Y/Ho ratios and other characteristics of the Nui Phao deposit, we propose a single magmatic source for hydrothermal ore-firming fluids without fluid mixing; a significantly contribution of material during fluid/rock interaction is also unlikely. The combination of mineralogical and geochemical features as well as complex studies of the formation conditions allowed us to conclude that gold at the Nui Phao deposit occur as impurities in the native bismuth. The ages of the Da Lien and Nui Phao granite massifs and the Nui Phao deposit have been estimated to be ca. 84 Ma (Ar-Ar), 244 Ma (U-Pb) and ca. 85 Ma (Ar-Ar), respectively, indicating a genetic relationship between the mineralization and the Cretaceous magmatic event.

Nature and ore formation of the Erdaohezi Pb-Zn deposit in the Great Xing’an Range, NE China

The Erguna metallogenic belt is a large Erdaohezi epithermal polymetallic sulfide Pb-Zn deposit in the northern Great Xing’an Range that is associated with andesitic porphyry. Mineralization mainly occurs at the edges of andesitic porphyry and adjacent Jurassic quartz porphyry and volcanic strata. Hydrothermal alteration minerals mainly include quartz, sericite, adularia, chlorite and calcite, while ore minerals include pyrite, galena and sphalerite, with minor argentite, chalcopyrite and tetrahedrite. Three hydrothermal-mineralization stages are recognized. Three categories of fluid inclusions (FIs) are distinguished in quartz, fluorite and sphalerite veins: liquid-rich, gas-rich and a few H2O–CO2 inclusions. The stage I FIs include all three inclusion types and present high homogenization temperatures (197–233℃) and salinities (0.7–6.8 wt% NaCl eq.). The stage II FIs mainly comprise liquid-rich inclusions with a few H2O–CO2 types and present higher homogenization temperatures (167–190℃) and slightly higher salinities (0.9–7.6 wt% NaCl eq.) than those of stage I. Stage III only contains liquid-rich inclusions and presents the lowest homogenization temperatures (120–157℃) and salinities (0.5–4.8 wt% NaCl eq.). The ore-forming fluids have low temperatures and salinities in an H2O–NaCl–CO2 ± CH4 system. The O–H isotope data (-2.2 to −5.0‰ and −160.0 to −152.5‰, respectively) suggest that ore-forming fluids gradually evolved from mantle primarywater to meteoric water. Sulfur, strontium and lead isotopes imply a mixed crustal and mantle source for the ore-forming materials. Sulfide Rb–Sr dating yields a well-defined isochron age of 130.5 ± 3.6 Ma from the main mineralization stage, which is similar to the zircon age of 134.9 ± 0.9 Ma for the andesitic porphyry related to mineralization. We therefore proposed that Erdaohezi is a low-sulfidation epithermal Pb-Zn polymetallic deposit, and fluid immiscibility was the dominant mechanism of ore deposition. Mineralization occurred in an Early Cretaceous back-arc extensional setting that was related to the subduction of the Paleo-Pacific Plate.

Wax deposition mechanisms and the effect of emulsions and carbon dioxide injection on wax deposition: Critical review

Wax deposition inside the tubing walls endures being a critical operational challenge faced by the petroleum industry. The build-up of wax deposits may lead to the increase of pumping power, as well as the decrease of flow rate or, even, to the total blockage, with production losses and high operational costs. The current paper is a critical review of the main deposition mechanisms involved in wax deposition. Most of wax deposition models regard molecular diffusion as the dominant wax deposition mechanism. However, there are other deposition mechanisms which can also play a role. As most oil fields produce water along with crude oil, the deposition process for oil-water emulsions has also been investigated. Furthermore, carbon dioxide injection effects upon wax appearance temperature along its current applications onto wells have been reviewed. Having a total awareness of the wax deposition mechanisms background is the key factor to prevent the wax precipitation and control the deposition of solid wax crystals.

Inertial and gravitational effects on aerosol deposition in the conducting airways

In most inhaled drug delivery applications, aerosol deposition in the upper airways occurs primarily via impaction. However, the effects of gravity become important as particle size increases and flow rate decreases. Sedimentation can therefore be significant in the smaller airways of the tracheobronchial tree, where velocities decrease due to the large increase in cross-sectional area, as well as the larger airways at low inhalation flow rates. In order to assess the relative importance of impaction and sedimentation, particle transport and deposition is examined under different steady inhalation conditions in a mouth-throat and a bifurcation model, using direct numerical simulations. The results are also compared to computations without the effect of gravity on the particles. Two important parameters characterize particle motion: (i) the Stokes number, Stk, and (ii) the ratio of the gravitational settling velocity to the fluid velocity, Vg*. The ratio of these two parameters is the Froude number, which measures the relative importance of inertial to gravitational forces. Instantaneous definitions of the Stokes number, non-dimensional settling velocity and Froude number are derived, based on the local flow properties, which provide a more accurate representation of the particle trajectories compared to the reference parameters based on characteristic flow scales. Results show that, in certain regions of the flow, the instantaneous Froude number can be three to four orders of magnitude smaller than the reference value. In these regions, deposition via sedimentation is shown to be significant, and the reference parameter underestimates gravitational effects. In the extrathoracic airways, particles with high Vg* deposit primarily in the mouth, via sedimentation, while particles with high Stk deposit mainly in the larynx and trachea, via impaction. In the bifurcation, different orientation angles of the airway geometry are shown to result in non-negligible variation in deposition. Impaction is the dominant mechanism for deposition on the carinal ridge, while sedimentation occurs along airway walls at an angle to the gravity direction. In the daughter branches, both impaction and sedimentation contribute to deposition.

Kinetics of Silane Decomposition in High-Pressure Confined Chemical Vapor Deposition of Hydrogenated Amorphous Silicon

We study the kinetics of silane pyrolysis via confined high-pressure chemical vapor deposition (HPCVD) at pressures of 20–33 MPa in a microcapillary of 5.9 μm inner diameter. We find the growth rate to be first order with respect to silane concentration, with an activation energy of 53.7 ± 2.9 kcal/mol and a pre-exponential factor of 1.5 × 1010 m/s. The obtained activation energy is in the range of activation energies reported for hydrogen desorption from c-Si surfaces, suggesting that hydrogen desorption from the surface is the rate-limiting step in film growth. To further investigate this finding, reactive molecular dynamics simulations of thermal decomposition of silane on clean and hydrogen-passivated c-Si were performed. Homogeneous reactions were not observed in any of the simulations, in support of the hypothesis that heterogeneous silane decomposition on the silicon surface is the dominant mechanism for film deposition. In silane pyrolysis simulations on clean c-Si surfaces, almost all available s...

Altitudinal characteristics of atmospheric deposition of aerosols in mountainous regions: Lessons from the Fukushima Daiichi Nuclear Power Station accident

To understand the formation process of radiologically contaminated areas in eastern Japan caused by the Fukushima Daiichi Nuclear Power Station (FDNPS) accident, the deposition mechanisms over complex topography are the key factors to be investigated. To characterize the atmospheric deposition processes of radionuclides over complex mountainous topography, we investigated the altitudinal distributions of the radiocesium deposited during the accident. In five selected areas, altitudinal characteristics of the air dose rates observed using airborne surveys were analyzed. To examine the deposition mechanisms, we supplementarily used vertical profiles of radiocesium deposition in each area calculated in the latest atmospheric dispersion model. In southern Iwate, the vertical profile of the observed air dose rate was uniform regardless of altitude. In western Tochigi, the areas with the highest levels of contamination were characteristically distributed in the middle of the mountains, while in southern Fukushima, the areas with the highest contamination levels were enhanced near the summits of mountains. In central Fukushima, high air dose rates were limited to the bottoms of basin-like valley. In the region northwest of FDNPS, the air dose rate was the highest at the bottom of valley topography and decreased gradually with altitude. The simulation results showed that calculated wet deposition and observed vertical profiles of total deposition were similar in areas of southern Iwate and northwest of FDNPS qualitatively, suggesting that the dominant deposition mechanism was wet deposition. In contrast, the atmospheric dispersion model failed to reproduce either the timing of precipitation events or vertical profiles of radiocesium deposition in three other areas. Although it was difficult to elucidate the deposition mechanisms in these areas due to uncertainties of the present model results, potential mechanisms such as cloud water deposition were still proposed based on circumstantial evidences of limited meteorological data during the early stage of the accident.

Deposition of Inorganic Carbonate, Sulfate, and Sulfide Scales on Antifouling Surfaces in Multiphase Flow

Impairment of flow by way of mineral scale formation is a major complication affecting production in the oil and gas industry. Soured reservoirs contain hydrogen sulfide (H2S) that can prompt the formation of exotic metal sulfide scales, leading to detrimental fouling that can negatively impact production. The contrast in the mode of precipitation (solid formation from liquid solution) and deposition of both sulfide scale and conventional inorganic carbonate and sulfate scales is herein examined. Design of an experimental rig allowing diffusion of H2S gas into the brine phase of a sealed reaction vessel resulted in a realistic representation of scaling processes occurring within sour reservoirs. Multiphase conditions, induced by introduction of a light oil phase to scaling brine within a turbulent regime, aimed to study the effect of oil and water wetting on pipeline fouling. Performance of a range of antifouling surfaces was determined through measurement of scale deposition by gravimetry and microscopy techniques. Under conditions modeled to reflect a typical H2S-containing reservoir, the contrasting scaling mechanisms of conventional calcium carbonate (CaCO3) and barium sulfate (BaSO4) scales when compared to lead sulfide (PbS) scale highlighted the critical role of the light oil phase on deposition. While conventional scales showed deposition by both crystallization and adhesion onto surfaces, the thermodynamic driving force for PbS prompted rapid bulk nucleation, with adhesion acting as the overwhelmingly dominant mechanism for deposition. The results showed that the addition of a 5% v/v light oil phase had a profound effect on scale particle behavior and deposition onto antifouling surfaces of varying wettability as a result of two processes. Primarily, the oil wetting of hydrophobic surfaces acted as a barrier to deposition, and second, adsorption of scale crystals at the oil/water interface of oil droplets within a turbulent oil-in-water emulsion resulted in adhesion to hydrophilic surfaces after impaction. It is therefore proposed that sulfide scale, typically deposited in the upper regions of production tubing, is driven by adhesion after formation of a PbS solid-stabilized Pickering emulsion. This contrasts with the commonly held view that metal sulfides precipitate and deposit similarly to conventional scales, whereby salts crystallize both directly upon surfaces and in the aqueous bulk phase as solubility decreases toward the wellhead.

Numerical investigation of particle deposition in a triple bifurcation airway due to gravitational sedimentation and inertial impaction

Focusing on the particle deposition due to gravitational sedimentation and inertial impaction, the transport and deposition of micron particles with various diameters (i.e., 1 to 7μm) have been simulated in a triple bifurcation airway at flow rates of 15 to 120L/min. The airway configurations for generation 11 to generation 14 are determined by matching the Stokes number St and the sedimentation parameter γ (Particuology, 2016, 28:102–113). Air flow distributions, local deposition patterns, and deposition efficiencies are compared between simulations with and without gravity. The results suggest that minimum deposition efficiency exists for large particles indicating the change of dominant deposition mechanism between sedimentation and impaction. Sedimentation governed particle deposition is also observed for small particles. A revised correlation for predicting DE as a function of Stokes number and sedimentation parameter is proposed for 5.78×10−4<St<0.226 and 1.54×10−4<γ<0.06. These findings could be utilized to design the drug particle property and inhalation waveform for the high-efficiency pulmonary drug delivery.

Particle deposition in tracheobronchial airways of an infant, child and adult

BackgroundParticle deposition in human airways is important for assessing both health effects of inhaled particles and therapeutic efficacy of inhaled drug aerosols, but is not well understood for infants and children. ObjectiveWe investigate particle deposition in infants and children by using computational fluid dynamics (CFD), and compare this with particle deposition in adults. MethodsWe chose three population age groups: 7-month infant, 4-year old child, and 20-year old adult. Both airway structures and breathing conditions are considered to vary as a human grows from infancy to adulthood. We investigated deposition of micron-size particles (1–10μm) in both the upper (G3–G6) and lower (G9–G12) tracheobronchial (TB) airways under sedentary conditions. ResultsWe found that particle deposition in both upper and lower airways is the highest in an infant, next in a child, and lowest in an adult. As age increases, particle deposition decreases in the upper airways but increases in the lower. For infants, inertial impaction is the dominant deposition mechanism, thus particles are deposited more in the upper airways than in the lower. However, particles are deposited more in the lower airways than in the upper in adults, as gravitational sedimentation is the dominant deposition mechanism. ConclusionGiven the differences in the airway structure and particle deposition mechanisms, particle deposition in infants and children differs from that in adults, not only in the efficiency of deposition but also in the site. Our findings provide evidence that “children are not small adults”.

Mineralogical, petrographic and fluid inclusion evidence for the link between boiling and epithermal Ag-Au mineralization in the La Luz area, Guanajuato Mining District, México

Theoretical, experimental and observation data provide strong evidence that boiling is the dominant depositional mechanism in many low to intermediate sulfidation epithermal precious metals deposits. Textural and petrographic features that are evidence for boiling in the epithermal environment include the presence of coexisting liquid-rich and vapor-rich fluid inclusions, assemblages consisting of only vapor-rich fluid inclusions, colloform quartz, adularia and bladed calcite. We have examined 213 samples collected from surface outcrops, underground workings and drill cores from the central part of the La Luz vein system in the Guanajuato mining district, Mexico. In each sample, the various features that are evidence of boiling have been recorded. These observations have been quantified using a Boiling Confidence Factor that provides a means of scoring and rating each sample or area relative to the likelihood that boiling occurred.Homogenization temperatures of liquid-rich fluid inclusions within assemblages of coexisting liquid-rich and vapor-rich fluid inclusions have been measured to estimate the depth of trapping of the inclusions, and these data have been used to estimate the depth to the 300°C isotherm along the La Luz vein system.Fluid inclusions and mineral textural features show strong evidence of boiling in the deepest levels sampled in the La Luz system. This observation suggests that the bottom of the boiling zone is at some depth beneath the deepest levels explored and opens the potential for additional resources at depth.

Large eddy simulation of inertial fiber deposition mechanisms in a vertical downward turbulent channel flow

The deposition pattern of elongated inertial fibers in a vertical downward turbulent channel flow is predicted using large eddy simulation and Lagrangian particle tracking. Three dominant fibers deposition mechanisms are observed, namely, diffusional deposition for small inertial fibers, free‐flight deposition for large inertial fibers, and the interception mechanism for very elongated fibers. The fibers are found to exhibit orientation anisotropy at impact, which is strongly dependent on the fiber elongation. An increase in the fiber elongation increases the wall capture efficiency by the interception mechanism. The diffusional deposition mechanism is shown to dominate for fibers with large residence time, , in the accumulation zone and small deposition velocities, , while the free‐flight mechanism governs deposition for fibers with small and large . This study describes how particles deposit on a surface and, ultimately for many practical applications, how such deposition may promote fouling. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1451–1465, 2017

Details of regional particle deposition and airflow structures in a realistic model of human tracheobronchial airways: two-phase flow simulation

In the present investigation, detailed two-phase flow modeling of airflow, transport and deposition of micro-particles (1–10µm) in a realistic tracheobronchial airway geometry based on CT scan images under various breathing conditions (i.e. 10–60l/min) was considered. Lagrangian particle tracking has been used to investigate the particle deposition patterns in a model comprising mouth up to generation G6 of tracheobronchial airways. The results demonstrated that during all breathing patterns, the maximum velocity change occurred in the narrow throat region (Larynx). Due to implementing a realistic geometry for simulations, many irregularities and bending deflections exist in the airways model. Thereby, at higher inhalation rates, these areas are prone to vortical effects which tend to entrap the inhaled particles. According to the results, deposition fraction has a direct relationship with particle aerodynamic diameter (for dp=1–10µm). Enhancing inhalation flow rate and particle size will largely increase the inertial force and consequently, more particle deposition is evident suggesting that inertial impaction is the dominant deposition mechanism in tracheobronchial airways.