Aerosol Velocity Research Articles

Influence of modeling conditions on the estimation of the dry deposition velocity of aerosols on highly inhomogeneous surfaces

An approach to estimating the dry deposition velocity of aerosol particles on the surfaces of Arctic regions, where snow-covered surfaces, open water surface, tundra and coniferous forest predominate, is proposed and numerically investigated. Optimal modeling conditions are proposed, taking into account the characteristic sizes and densities of aerosol particles involved in transport in the planetary boundary layer, and the interaction of air flows with the surface through the parameter u*, calculated using the WRF-ARW model. The proposed approach is compared with other known models and experimental data. The dependence of the dry deposition velocity obtained by the proposed approach on the diameter, density of aerosol particles and dynamic velocity u* for the surfaces in the Far North is estimated.

Influence of Modeling Conditions on the Estimation of the Dry Deposition Velocity of Aerosols on Highly Inhomogeneous Surfaces

Influence of Modeling Conditions on the Estimation of the Dry Deposition Velocity of Aerosols on Highly Inhomogeneous Surfaces

Aerosol Plumes of Inhalers Used in COPD.

The selection of inhaler device is of critical importance in chronic obstructive pulmonary disease (COPD) as the interaction between a patient's inhalation profile and the aerosol characteristics of an inhaler can affect drug delivery and lung deposition. This study assessed the in vitro aerosol characteristics of inhaler devices approved for the treatment of COPD, including a soft mist inhaler (SMI), pressurized metered-dose inhalers (pMDIs), and dry powder inhalers (DPIs). High-speed video recording was used to visualize and measure aerosol velocity and spray duration for nine different inhalers (one SMI, three pMDIs, and five DPIs), each containing dual or triple fixed-dose combinations of long-acting muscarinic receptor antagonists and long-acting β2-agonists, with or without an inhaled corticosteroid. Measurements were taken in triplicate at experimental flow rates of 30, 60, and 90 l/min. Optimal flow rates were defined based on pharmacopoeial testing requirements: 30 l/min for pMDIs and SMIs, and the rate achieving a 4-kPa pressure drop against internal inhaler resistance for DPIs. Comparison of aerosol plumes was based on the experimental flow rates closest to the optimal flow rates. The Respimat SMI had the slowest plume velocity (0.99 m/s) and longest spray duration (1447 ms) compared with pMDIs (velocity: 3.65-5.09 m/s; duration: 227-270 ms) and DPIs (velocity: 1.43-4.60 m/s; duration: 60-757 ms). With increasing flow rates, SMI aerosol duration was unaffected, but velocity increased (maximum 2.63 m/s), pMDI aerosol velocity and duration were unaffected, and DPI aerosol velocity tended to increase, with a more variable impact on duration. Aerosol characteristics (velocity and duration of aerosol plume) vary by inhaler type. Plume velocity was lower and spray duration longer for the SMI compared with pMDIs and DPIs. Increasing experimental flow rate was associated with faster plume velocity for DPIs and the SMI, with no or variable impact on plume duration, whereas pMDI aerosol velocity and duration were unaffected by increasing flow rate.

Laser doppler device for simultaneous measurement of the velocity and size of aerosols in the nozzle flame

Liquid aerosol is used in technological processes in mechanical engineering, instrument building, chemical industry, medicine and agriculture and other areas. Nozzles are used to spray liquids, which allow to obtain their uniform distribution on the surface or in the volume. In aviation jet engines, fuel is sprayed using nozzles. The thrust of an aircraft engine depends on the quality of fuel atomization. Information on the distribution of droplet sizes and their movement velocity is required to assess the properties of the entire droplet-air system of the nozzle torch. To determine the main characteristics of the nozzle, you need to have a device that measures the velocity of aerosols and the size of aerosols in the nozzle flame. In order to solve this problem, the possibility of using a laser Doppler velocitymeter is investigated. Analysis of the radiation scattered by aerosols by intensity and state of polarization was carried out. It is proposed to increase the signal/interference ratio of the device by ensuring the matching of scattered radiation by intensity and polarization state. For this purpose, it is proposed to install a spatial filter of scattered laser radiation in the device. Such a filter should have the form of a diaphragm with two holes in the form of a narrow slit. Within the limits of one hole, the condition of complete matching of radiation in terms of intensity will be fulfilled, and within the limits of the other hole, the condition of matching according to the state of polarization will be fulfilled. It is shown that if such a receiving diaphragm is inserted into a differential-type laser velocity meter, it can be used to simultaneously measure the velocity and size of aerosols in the nozzle plume. The laser velocity meter photo detector must contain a built-in amplifier with a wide bandwidth. Doppler signals must then be sent simultaneously to an amplitude detector and a digital device. Using a digital device, the frequency of the variable component of the signal will be measured, which is proportional to the velocity of the aerosol and the amplitude of the signal is measured which is proportional to the size of the aerosol.

The impact of actuator nozzle and surroundings condition on drug delivery using pressurized-metered dose inhalers.

The most commonly used method to deliver aerosolized drugs to the lung is with pressurized metered-dose inhalers (pMDIs). The spray actuator is a critical component of pMDI, since it controls the atomization process by forming aerosol plumes and determining droplet size distribution. Through computational fluid dynamics (CFD) simulations, this study investigated the effect of two different nozzle types (single conventional and twin nozzles) on drug deposition in the mouth-throat (MT) region. We also studied the behavior of aerosol plumes in both an open-air environment and the MT geometry. Our study revealed that spray aerosol generated in an unconfined, open-air environment with no airflow behaves distinctly from spray introduced into the MT geometry in the presence of airflow. In addition, the actuator structure significantly impacts the device's efficacy. In the real MTmodel, we found that the twin nozzle increases drug deposition in the MT region, and its higher aerosol velocity negatively affects its efficiency.

Evaluation of Soft Mist Inhaler Aerosol Velocity, Size, and Deposition Inside the Mouth-A Computational Fluid Dynamics Study.

Respiratory diseases debilitate more than 250 million people around the world. Among available inhalation devices, the soft mist inhaler (SMI) is the most efficient at delivering drugs to ease respiratory disease symptoms. In this study, we analyzed the SMI performance in terms of the aerosol's velocity profiles, flow pattern, size distribution, and deposition by employing computational fluid dynamics (CFD) simulations. We modeled two different simplified mouth geometries, idealized mouth (IM), and standard mouth (SM). Three different locations (x = 0, x = 5, and x = 10 mm) for the SMI nozzle orifice were chosen along the mouth cavity centerlines, followed by two different SMI nozzle angles (10 deg and 20 deg) for IM geometry. A flowrate of 30 L/min was applied. The simulation results were evaluated against experimental data. It was found that the SMI could be simulated successfully with a level of error of less than 10%. The inhalation flowrate significantly impacted the aerosol's velocity profile and deposition efficiency on both the IM and SM walls. The lowest particle deposition on the mouth wall occurred when a fixed flowrate (30 L/min) was applied inside both geometries, and the SMI nozzle position moved forward to x = 10 mm from the IM and SM inlets. An increase in the SMI nozzle angle increased particle deposition and decreased the deposition fraction for particles with a diameter above 5 μm inside the IM.

On-line measurement for velocity and particle size distribution of flowing aerosol by dynamic light scattering

In the dynamic light scattering (DLS) measurement for a flowing aerosol, an anemometer, is needed to measure the flow velocity to invert the aerosol particle size. In this work, a cumulative analysis method has been used to obtain the aerosol velocity through the light intensity autocorrelation function (ACF) based on the relation between the particle velocity and the second cumulant of the electric field ACF of flowing aerosol particles. Additionally, the particle size distribution (PSD) has been inversed by the regularization method, which enables the online measurement of flowing aerosol to be realized. The simulation results at different noise levels show that the accurate velocity and PSD for flowing aerosols can be obtained by the proposed method at low noise levels and high noise levels. It has been observed that higher noise causes the PSD broadening and the peak offset. For aerosol particles with a bimodal distribution, the increase of noise leads to the increase of peak height ratio and peak of small particles in bimodal distribution disappears, leaving only unimodal distribution. Furthermore, the increase of noise has no significant effect on the calculated velocity value both for unimodal and bimodal aerosol distributions. The experimental results of DLS measurements on unimodal and bimodal aerosols verified the above statements.

10-Years assessment of 7Be and 210Pb in atmospheric bulk depositions in Cienfuegos (Cuba)

10-years records of monthly bulk atmospheric fluxes of 7Be and 210Pb (wet + dry, n = 119 samples) at a coastal station in Cienfuegos (Cuba) between 2010 and 2019 were reported and assessed in function of their temporal variability and meteorological influence. Fluxes of 7Be and 210Pb ranged from 120 to 15617 and from 29 to 911 mBq m−2 day−1, respectively. Both radionuclides exhibited a similar seasonal trend with highest values during wet months and minimum values during dry months. The removal of 7Be and 210Pb from the atmosphere was mainly controlled by wet depositions, while dry deposition was estimated to be more important for 210Pb (29% of the total bulk deposition) than for 7Be (12%). The 210Pb/7Be ratios (average of 0.10) showed low variability during wet months with abrupt peaks in the driest months with low temperatures and the highest wind speed and pressure, which was mainly attributed to contributions from soil resuspension. The calculated total deposition velocity of aerosols derived from 7Be (average of 0.48 cm s−1) and 210Pb (average of 0.47 cm s−1) was in agreement with values reported in the literature. Multiple linear regression models for the monthly fluxes of 7Be and 210Pb based on precipitation, temperature and pressure and explaining about 60% of their variances were derived, highlighting the preponderant role of the local and regional conditions on the variability of these radionuclides. The annual fluxes of 7Be (209–1901 Bq m−2 y−1) and 210Pb (35–123 Bq m−2 y−1) were in the range of variations observed in other coastal stations worldwide, showing fluctuations affected by changes in the amount of precipitation during the wet periods. 7Be annual variability also evidenced a significant modulation with the solar activity.

What are the effects of portable air cleaners with a high-efficiency particulate air filter on aerosol removal in dental surgeries?

Design Volumetric air flow was measured in a number of dental surgeries to calculate the air change rate per hour (ACHvent). In each surgery, measurements of aerosol removal by ventilation alone, and then with ventilation provided by a high-efficiency particulate air filter (PAC), were completed. The concentrations of aerosol particles of various sizes were recorded at baseline, after an initial period of incense burn, and then after 30 minutes of observation with and without the use of the PAC or ventilation system.Sample selection Ten dental surgeries with differing baseline ventilation rates had the concentrations of 0.3, 0.5 and 1.0 μm aerosol particles measured at 0 minutes, after 5 minutes of incense burn and then after 30 minutes of observation, firstly without the PAC system in operation and then with the PAC system in use.Data analysis For the 0.3 μm particles, velocities of aerosol removal were assessed by analysing the concentration decay constants with ventilation alone and ventilation with the PAC. Aerosol removal velocities were assessed by the time needed to reach 95% and 100% removal of accumulated aerosol particles.Results ACHvent in the ten different surgeries varied from 3-45. The concentration decay constants for the 0.3 μm particles with ventilation alone and ventilation with the PAC were correlated to the mechanical ventilation rate and combined respectively. For rooms with ACHvent of less than 15, accumulated aerosol particles could not be removed by ventilation alone in 30 minutes. The PAC accelerated aerosol removal and reduced aerosol accumulation, and with the use of the PAC in addition to ventilation, accumulated aerosols were removed completely in 4-12 minutes. The PAC was shown to be more beneficial in rooms with poor ventilation and the added effectiveness of the PAC in aerosol removal was inversely correlated with the ACHvent by ventilation.Conclusions Although the air change rate differed considerably among dental surgeries, this study suggests that the addition of the PAC with a HEPA filter significantly increased aerosol removal and lessened aerosol accumulation, particularly in rooms with low ventilation rates.

Dry deposition velocities of particles on grass: Field experimental data and comparison with models

Aerosols emitted into the atmosphere are dispersed by atmospheric air masses and then removed by dry or wet deposition processes. In some cases, if there are no episodes of precipitation, dry deposition may be the main processes in particular on a local scale. Dry deposition is characterized by the dry deposition velocity Vd (m.s−1), which is generally standardized at the friction velocity u* (m.s−1). From 2005–2016, we conducted experimental campaigns on-site with fluorescein tracer to determine dry deposition velocity of aerosols on grass. The particle sizes tested were 0.24, 0.27, 0.5, 0.6, 1.2, 3, and 7.8 µm. We described here the experimental method, the results obtained in terms of Vd/u* by particle size and we compared our results to the values usually simulated from the main models used by the scientific community. The results show that the Vd/u* parameter varies in a range from 2 to 6 10−3 for particle diameters from 0.2 to 1.2 µm. Beyond 1.2 µm the Vd/u* ratio increases rapidly with a value of 5.4 10−2 to 7.8 µm. Based on our experimental results, Vd/u* relationships were proposed for potential applications in operational models for a grass-type rural cover, which has a constant mean value of 3.7 ± 1.9 10−3 for particles in the size range of 0.2 and 1.2 µm, and as a linear function of particle size (Dp, diameter) expressed as 0.0082 × [Dp]− 0.0106 for larger particles between 1.2 and 8 µm.

Enhancement of PM2.5 Concentrations by Aerosol‐Meteorology Interactions Over China

AbstractAerosol‐meteorology interactions can change surface aerosol concentrations via different mechanisms such as altering radiation budget or cloud microphysics. However, few studies investigated the impacts of different mechanisms on temporal and spatial distribution of PM2.5 concentrations over China. Here we used the fully coupled Weather Research and Forecasting model with online chemistry (WRF‐Chem) to quantify the enhancement of PM2.5 concentrations by aerosol‐meteorology feedback in China in 2014 for different seasons and separate the relative impacts of aerosol radiation interactions (ARIs) and aerosol‐cloud interactions (ACIs). We found that ARIs and ACIs could increase population‐weighted annual mean PM2.5 concentration over China by 4.0 μg/m3 and 1.6 μg/m3, respectively. We found that ARIs play a dominant role in aerosol‐meteorology interactions in winter, while the enhancement of PM2.5 concentration by ARIs and ACIs is comparable in other three seasons. ARIs reduced the wintertime monthly mean wind speed and planetary boundary layer (PBL) height by up to 0.1 m/s and 160 m, respectively, but increased the relative humidity by up to 4%, leading to accumulation of pollutants within PBL. Also, ARIs reduced dry deposition velocity of aerosols by up to 20%, resulting in an increase in PM2.5 lifetime and concentrations. ARIs can increase wintertime monthly mean surface PM2.5 concentration by a maximum of 30 μg/m3 in Sichuan Basin. ACIs can also increase PM2.5 concentration with more significant impacts in wet seasons via reduced wet scavenging and enhanced in‐cloud chemistry. Dominant processes in PM2.5 enhancement are also clarified in different seasons. Results show that physical process is more important than chemical processes in winter in ARIs, while chemical process of secondary inorganic aerosols production may be crucial in wet seasons via ACIs.

7Be, 210Pb and 40K depositions over 11 years in Málaga

The monthly bulk depositional fluxes of three natural radionuclides (7Be, 210Pb and 40K) were measured at a Mediterranean coastal station (Málaga) over an 11-year period from 2005 to 2015. The mean annual depositional fluxes of 7Be, 210Pb and 40K were 1215, 144 and 67 Bq m−2 year−1 respectively, showing a clear seasonal trend with minimum values recorded during summer and maximum values in winter. The rainfall regime with dry summers allows estimating the dry deposition. Assuming constant dry deposition through each year, 7Be, 210Pb and 40K would account for 12.5, 26.5 and 33% of the bulk fallout respectively which indicates that deposition for 210Pb and 40K are significantly higher than 7Be. The precipitation-normalized enrichment factor alpha used to explain seasonal variations in the depositional fluxes of radionuclides with respect the rainfall, indicates higher depositional fluxes during spring and summer than expected from the amount of rainfall. Despite their different origin, 210Pb and 7Be monthly depositional fluxes have strong correlation. The atmospheric deposition fluxes of 7Be, 210Pb and 40K were controlled mainly by the amount of rainfall (r = 0.89, 0.91 and 0.66 respectively). Moreover, principal component analysis was applied to the datasets and deposition of radionuclides and rainfall in the same component highlighting the importance of the washout mechanism. The mean depositional velocity of aerosols evaluated using 7Be and 210Pb are similar and are compared to other published values.

The impact of re-entrainment on the electrocyclone effectiveness

Abstract The problem of fine particle gas cleaning is especially actual at the present time. This is due to the need to capture the desired product and waste gases cleaning. In both cases, the equipment should provide maximum collection efficiency. Cleaning of gas from thermal power plant (TPP) fly ash is serious problem. Coal-fired thermal power plants provide 27% of the total world energy consumption. Conventional TPP produce more than 700,000 tonnes of fly ash per year. Annually fly ash production only in Russia, according to various estimates, is 27–35 million tons. Various apparatus are used to clean the gases from the fly ash. Required collection efficiency of purification units must to be 99.5–99.7% and higher. Wet scrubbers makes ash recycling more difficult. It requires ash separation from the slurry and drying. One solution of gas cleaning problem is a electrocyclone. It provides gas purification efficiency up to 99.9% at initial ash concentration equal 50 g/m 3 and higher. An electrocyclone allows to obtain a product in dry form. Re-entrainment is return of captured material to clean gas stream. Re-entrainment in the gas cleaning equipment is one of the negative effects. Re-entrainment reduces equipment efficiency at high gas velocities. The present study was carried out to determine the value of re-entrainment in the electrocyclone. The object of study was the electrocyclone of ‘pipe in pipe’ type. Aluminosilicate fly ash from thermal power plant (TPP) was the test material. Study was carried out in dry and wet modes. Re-entrainment was observed in dry operation mode. No re-entrainment was observed in wet operation mode. The value of re-entrainment was calculated. It decreases collection efficiency from 99.9% to 60%. Re-entrainment depends on aerosol velocity (range 14–27 m/s) and the aerosol concentration (range 2–30 g/m 3 ). It is shown, what re-entrainment can be eliminated by water irrigation of collecting electrodes.

The importance of inhaler devices in the treatment of COPD

Chronic obstructive pulmonary disease (COPD) represents a socio-economic burden and requires regular and ongoing treatment. Inhalation therapy is recommended at all stages of the disease and allows the delivery of active molecules directly to the target site of action, whilst minimising adverse side-effects. Inhalers therefore play a crucial role in the effective management of patients with COPD and their choice is as important as that of the drug. The three most important factors that influence inhaled drug deposition within the airways are the patient’s inhalation flow, the aerosol velocity, and the inhaled drug particle size. These ultimately impact on the amount of drug reaching the target site and therefore the functional and clinical responses of the patient. Furthermore, patients’ training and education in the use of inhalers have been shown to be directly related to the efficacy of the therapy. However, in daily clinical practice, too little consideration is given to the features of the different inhalers and to the ability of patients to properly handle the device, and precise recommendations are greatly needed to help healthcare professionals to advise and prescribe the most ‘appropriate’ inhaled drug/device product. The present review aims to provide the latest evidence on the importance of the inhaler device in the management of patients with COPD.

Effects of ocean particles on the upwelling radiance and polarized radiance in the atmosphere-ocean system

Based on a vector radiative transfer model of the atmosphere-ocean system, the influence of oceanic components on radiation processes, including polarization effects, was investigated in the wavelength region ranging from 0.380 to 0.865 μm. The components considered were phytoplankton, inorganic suspended material (sediment), and colored, dissolved organic matter. Due to their important roles in oceanic radiation processes, the sensitivity of the bidirectional reflectance to the rough ocean surface, represented by the wind velocity 10 m above the ocean surface, and aerosol, were taken into account. The results demonstrated that both radiance and polarized radiance just below the ocean surface were sensitive to the change of the concentrations of the considered components, while the dependence of polarized radiance on the observation geometry was more sensitive than radiance. Significant differences in the specular plane existed between the impacts of the phytoplankton and sediment on the degree of polarization just above the ocean surface at 670 nm. At the top of the atmosphere (TOA), polarization was relatively insensitive to changing concentrations of ocean particles at longer wavelengths. Furthermore, the radiance at the TOA in the solar plane was more sensitive to the aerosol optical thickness than wind velocity. In contrast, wind velocity strongly influenced the radiance at the TOA in the sun glint region, while the polarization degree showed less dependence in that region. Finally, a nonlinear optimal inversion method was proposed to simultaneously retrieve the aerosol and wind velocity using radiance measurement.

Raising the standard of care for oxygen delivery with nasal high flow in high-acuity areas—a controlled study

Nasal high-flow therapy and dispersion of nasal aerosols in an experimental setting Sally Roberts, N. Kabaliuk, Cjt Spence, Jane O'Donnell, Z. Zulkhairi Abidin, R. Dougherty, S. Roberts, Y. Jiang, Mc Jermy University of Canterbury, New Zealand Fisher & Paykel Healthcare, New Zealand University of KS, USA Auckland District Health Board, New Zealand University of Auckland, New Zealand Background/Purpose: Nasal high-flow (NHF) therapy delivers flows of heated and humidified gases up to 60 L/min via a nasal cannula. NHF is widely used to support patients, including those who may be infectious. It is thought that NHF gas flow velocities may increase cross-infection risk. Methods: Aerosols within the exhaled breath of healthy volunteers were imaged. Experimental breathing conditions deemed as typical patient breathing conditions were tested: at rest, with a violent exhalation (snorting), both with and without NHF, at flows of 30 and 60 L/min, and for both separate nostrils. The number, diameter, evaporation rates, and velocity of exhaled aerosols were collected. Results: The numbers of aerosols measured were greatest during a violent exhalation without NHF and reduced with NHF. The numbers of aerosols were higher at 60 than 30 L/min, suggesting that higher gas flow rates may be associated with increased aerosol production; however, the numbers were on average 43% and 56% less than without NHF, respectively. During breathing at rest, no differences were imaged between with and without NHF, except at 60 L/min where numbers of aerosols produced were equivalent to 10% of a violent exhalation. Aerosol trajectory and evaporation rates observed both with and without NHF predicted that aerosols between 25 and 250 μm may travel up to 4.4 m and remain airborne for 43 seconds. Conclusions: NHF use does not increase the risk of dispersing infectious aerosols above the risk of typical patient breathing with violent exhalation, which is the worst-case clinical scenario; therefore, standard risk control measures should apply.

Nasal high-flow therapy and dispersion of nasal aerosols in an experimental setting

Nasal high-flow therapy and dispersion of nasal aerosols in an experimental setting Sally Roberts, N. Kabaliuk, Cjt Spence, Jane O'Donnell, Z. Zulkhairi Abidin, R. Dougherty, S. Roberts, Y. Jiang, Mc Jermy University of Canterbury, New Zealand Fisher & Paykel Healthcare, New Zealand University of KS, USA Auckland District Health Board, New Zealand University of Auckland, New Zealand Background/Purpose: Nasal high-flow (NHF) therapy delivers flows of heated and humidified gases up to 60 L/min via a nasal cannula. NHF is widely used to support patients, including those who may be infectious. It is thought that NHF gas flow velocities may increase cross-infection risk. Methods: Aerosols within the exhaled breath of healthy volunteers were imaged. Experimental breathing conditions deemed as typical patient breathing conditions were tested: at rest, with a violent exhalation (snorting), both with and without NHF, at flows of 30 and 60 L/min, and for both separate nostrils. The number, diameter, evaporation rates, and velocity of exhaled aerosols were collected. Results: The numbers of aerosols measured were greatest during a violent exhalation without NHF and reduced with NHF. The numbers of aerosols were higher at 60 than 30 L/min, suggesting that higher gas flow rates may be associated with increased aerosol production; however, the numbers were on average 43% and 56% less than without NHF, respectively. During breathing at rest, no differences were imaged between with and without NHF, except at 60 L/min where numbers of aerosols produced were equivalent to 10% of a violent exhalation. Aerosol trajectory and evaporation rates observed both with and without NHF predicted that aerosols between 25 and 250 μm may travel up to 4.4 m and remain airborne for 43 seconds. Conclusions: NHF use does not increase the risk of dispersing infectious aerosols above the risk of typical patient breathing with violent exhalation, which is the worst-case clinical scenario; therefore, standard risk control measures should apply.

Aerosol-Size Spread Influence on Dissipative Instability of Aerosol Flows in the Planetary Atmospheres. I. Earth’s Mesosphere

The influence of aerosol-size spread on the dissipative instability of the aerosol flow in a cold weakly ionized collisional plasma is considered. The instability is generated by the relative motion of the aerosol and ion components due to the gravity fall of aerosols. The studies allow for the molecular ion diffusion, charging of large particles, and their size spread within the framework of three model distributions, i.e., monodisperse ensemble, power-law distribution, and Gaussian distribution. The threshold charge values on the aerosols, which are required for the instability development, are obtained as functions of the system parameters. The particle-size spread is shown to significantly increase the threshold charge value and qualitatively change its dependence on some parameters. In particular, it decreases with increasing aerosol velocity in the absence of spread, and the dependence of the threshold value on the parameters determining the aerosol velocity is at the minimum when the spread is allowed for. The threshold charge increases with increasing coefficient of ion diffusion. Qualitative estimates of the threshold charges and characteristic instability scales are obtained for the Earth’s mesospheric conditions at altitudes of 80 to 90 km.

Pollution accumulation on rail insulator in high-speed aerosol

Pollution distributes irregularly on the surfaces of traction power supply system insulators as high-speed trains pass through pollution aerosols. This affects the flashover characters. Insulator polluting characteristics were studied in a wind tunnel at speeds up to 100 m/s. The gas-solid aerosol flow around insulator was analyzed and a pollution accumulation model was established after analyzing the forces on dust particles. Additional simulation shows that with the aerosol velocity increases, pollution accumulates more on the windward side and leeside. Accumulation on the leeside increases as the crosswind side decreases. When viscosity and pollution density are constants, the quantity of pollution on upper surface of a post-type third-rail insulator shed is not so uniform, but has maximum and minimum values. This numerical modeling result corresponds well with experiment. A method is proposed to express the pollution distribution using ESDD and NSDD.

Investigation of Aerosol Mass and Number Deposition Velocity in a Closed Chamber

In the event of a core disruptive accident in a sodium cooled fast reactor, the Reactor Containment Building (RCB) is bottled-up with coolant (sodium), fuel and fission product aerosols. The aerosols suspended in the closed environment undergo coagulation and gravitational settling. Sodium aerosols are generated by combustion, while fission product aerosols are generated by vaporization and condensation, with the resulting particles having two flow regimes. It is expected that the mass concentration of sodium aerosols is relatively high, on the order of a few g/m 3 , while that of the fuel and fission products is only a few mg/m 3 . Taking into account the concentration criteria, experiments are carried out by generating sodium aerosols (mono dispersed) with the concentration of 3.0 g/m 3 , and the deposition velocity over time is determined by mass measurements (concentration and flux). Similarly, non-radioactive species of SrO2 aerosols are generated (mono dispersed) with a number concentration of 10 6 /cm 3 , and their deposition velocity over time is determined by number measurements (concentration and flux). The mass deposition velocity of sodium aerosols was found to be more than two orders of magnitude greater than the number deposition velocity of SrO2 aerosols. As the SrO2 aerosols are generated in the free molecular regime, the depletion pattern of the number concentration of suspended aerosols follows a process of simultaneous coagulation and settling. A theoretical formulation for the rate of depletion of the number concentration is developed, and the rate coefficients of coagulation and deposition velocity are determined from the theoretically fitted equation. The experimental and theoretical results are compared and found to be nearly same. The deposition velocity of sodium aerosols is used to predict the deposition time for the suspended aerosol mass concentration inside the RCB. The mass and number deposition velocities are determined by using a state of art Turn Table Instrument fabricated in our lab.