Variation Of Particle Concentration Research Articles

Theoretical prediction of electric fields in wind‐blown sand

Existing experimental and theoretical studies have identified the existence of an electric field in wind‐blown sand, whose strength is hundreds to thousands of times larger than that of the fair‐weather electric field (around 120v m− 1) and is related to the intensity of the wind‐blown sand transport. The direction of electric field is often upward pointing and opposite to that of the fair‐weather electric field. In this study, we performed theoretical predictions of electric fields in wind‐blown sand transport by assuming a constant charge‐to‐mass ratio (i.e., − 60µc kg− 1) of the saltating particles and considering the streamwise spatial variation of particle concentration in the evolution of wind‐blown sand. Our results show that there exist both vertical and horizontal electric fields in wind‐blown sand transport. The numerical results of vertical electric fields and mass flux are in good agreement with the experimental data measured by Schmidt et al. [1998] and Shao and Raupach [1992], respectively, which suggests that our model is valid. The horizontal electric field demonstrates a vertical stratification feature and is about one order of magnitude bigger than the fair‐weather electric field. Finally, the effects of the wind speed and the sand grain diameter on electric fields are discussed.

Effect of Flow Characteristics on Ultrafine Particle Emissions from Range Hoods

In order to understand the physical mechanisms of the production of nanometer-sized particulate generated from cooking oils, the ventilation of kitchen hoods was studied by determining the particle concentration, particle size distribution, particle dimensions, and hood's flow characteristics under several cooking scenarios. This research varied the temperature of the frying operation on one cooking operation, with three kinds of commercial cooking oils including soybean oil, olive oil, and sunflower oil. The variations of particle concentration and size distributions with the elevated cooking oil temperatures were presented. The particle concentration increases as a function of temperature. For oil temperatures ranging between 180°C and 210°C, a 5°C increase in temperature increased the number concentration of ultrafine particles by 20-50%. The maximum concentration of ultrafine particles was found to be approximately 6 × 10(6) particles per cm(3) at 260°C. Flow visualization techniques and particle distribution measurement were performed for two types of hood designs, a wall-mounted range hood and an island hood, at a suction flow rate of 15 m(3) min(-1). The flow visualization results showed that different configurations of kitchen hoods induce different aerodynamic characteristics. By comparing the results of flow visualizations and nanoparticle measurements, it was found that the areas with large-scale turbulent vortices are more prone to dispersion of ultrafine particle leakage because of the complex interaction between the shear layers and the suction movement that results from turbulent dispersion. We conclude that the evolution of ultrafine particle concentration fluctuations is strongly affected by the location of the hood, which can alter the aerodynamic features. We suggest that there is a correlation between flow characteristics and amount of contaminant leakage. This provides a comprehensive strategy to evaluate the effectiveness of kitchen hoods in capturing cooking oil fumes, which is based on an assessment of the entire hood face exposure instead of on breathing-zone sampling alone.

Variation in particle concentrations of nitrate and sulfate in Uji, Kyoto Prefecture

Variation in particle concentrations of nitrate and sulfate in Uji, Kyoto Prefecture

Particle number size distribution and new particle formation (NPF) in Lanzhou, Western China

Particle number size distribution from 10 to 10,000 nm was measured by a wide-range particle spectrometer (WPS-1000XP) at a downwind site north of downtown Lanzhou, western China, from 25 June to 19 July 2006. We first report the pollution level, diurnal variation of particle concentration in different size ranges and then introduce the characteristics of the particle formation processes, to show that the number concentration of ultrafine particles was lower than the values measured in other urban or suburban areas in previous studies. However, the fraction of ultrafine particles in total aerosol number concentration was found to be much higher. Furthermore, sharp increase of ultrafine particle concentration was frequently observed at noon. An examination of the diurnal pattern suggests that the burst of the ultrafine particles was mainly due to nucleation process. During the 25-day observation, new particle formation (NPF) from homogeneous nucleation was observed during 33% of the study period. The average growth rate of the newly formed particles was 4.4 nm/h, varying from 1.3 to 16.9 nm/h. The needed concentration of condensable vapor was 6.1 × 10 7 cm −3, and its source rate was 1.1 × 10 6 cm −3 s −1. Further calculation on the source rate of sulphuric acid vapor indicated that the average participation of sulphuric acid to particle growth rate was 68.3%.

Dimension reduction method for ODE fluid models

We develop a new dimension reduction method for large size systems of ordinary differential equations (ODEs) obtained from a discretization of partial differential equations of viscous single and multiphase fluid flow. The method is also applicable to other large-size classical particle systems with negligibly small variations of particle concentration. We propose a new computational closure for mesoscale balance equations based on numerical iterative deconvolution. To illustrate the computational advantages of the proposed reduction method, we use it to solve a system of smoothed particle hydrodynamic ODEs describing single-phase and two-phase layered Poiseuille flows driven by uniform and periodic (in space) body forces. For the single-phase Poiseuille flow driven by the uniform force, the coarse solution was obtained with the zero-order deconvolution. For the single-phase flow driven by the periodic body force and for the two-phase flows, the higher-order (the first- and second-order) deconvolutions were necessary to obtain a sufficiently accurate solution.

Volumetric-correlation PIV to measure particle concentration and velocity of microflows

Volumetric-correlation particle image velocimetry (VPIV) is a new technique that provides a 3-dimensional 2-component velocity field from a single image plane. This single camera technique is simpler and cheaper to implement than multi-camera systems and has the capacity to measure time-varying flows. Additionally, this technique has significant advantages over other 3D PIV velocity measurement techniques, most notably in the capacity to measure highly seeded flows. Highly seeded flows, often unavoidable in industrial and biological flows, offer considerable advantages due to higher information density and better overall signal-to-noise ratio allowing for optimal spatial and temporal resolution. Here, we further develop VPIV adding the capability to measure concentration and increasing the robustness and accuracy of the technique. Particle concentrations are calculated using volumetric auto-correlations, and subsequently the velocities are calculated using volumetric cross-correlation corrected for variations in particle concentration. Along with the ability to calculate the particle concentration profile, our enhanced VPIV produces significant improvement in the accuracy of velocity measurements. Furthermore, this technique has been demonstrated to be insensitive to out-of-plane flows. The velocity measurement accuracy of the enhanced VPIV exceeds that of standard micro-PIV measurements, especially in near-wall regions. The 3D velocity and particle-concentration measurement capability of VPIV are demonstrated using both synthetic and experimental results.

Wavelet packet analysis of particle response to turbulent fluctuation

The fluid–particle synchronous measurements in a boundary layer wind tunnel were conducted to determine the particle concentration response to turbulent velocity fluctuation. Three groups of natural sand samples (diameter of 300–500, 100–125 and 63–80μm) were employed in the experiments. Consecutive instants of saltating particles were recorded by using a high-speed digital camera at 2000 frames per second and a constant-temperature hot-wire anemometer was used to measure the turbulent fluctuation simultaneously. The particle concentration in the saltation layer was calculated by the dynamic-threshold binarization algorithm. The results confirm that the concentration fluctuation is a fairly typical stochastic process, and the low-frequency variation of particle concentration is closely related to the turbulent fluctuation. Moreover, a method was developed to apply wavelet packet transform to two-phase data analysis from the viewpoint of frequency-domain energy structure. Further analysis shows that the concentration fluctuation is predominant in the low frequency band less than 250Hz. In addition, the particle concentration response to the turbulent fluctuation is significantly correlated with the particle diameter. For the fine particles (63–80μm), medium particles (100–125μm) and coarse particles (300–500μm), the highest response frequencies of particle concentration variation to the turbulent fluctuation are 60, 40 and 30Hz, respectively, which demonstrates that an appropriate sampling rate is crucial in saltation measurement. These qualitative and quantitative results are beneficial to understand the fluid–particle interaction mechanism.

Improving suspended sediment measurements by automatic samplers

Suspended solids either as total suspended solids (TSS) or suspended sediment concentration (SSC) is an integral particulate water quality parameter that is important in assessing particle-bound contaminants. At present, nearly all stormwater runoff quality monitoring is performed with automatic samplers in which the sampling intake is typically installed at the bottom of a storm sewer or channel. This method of sampling often results in a less accurate measurement of suspended sediment and associated pollutants due to the vertical variation in particle concentration caused by particle settling. In this study, the inaccuracies associated with sampling by conventional intakes for automatic samplers have been verified by testing with known suspended sediment concentrations and known particle sizes ranging from approximately 20 μm to 355 μm under various flow rates. Experimental results show that, for samples collected at a typical automatic sampler intake position, the ratio of sampled to feed suspended sediment concentration is up to 6600% without an intake strainer and up to 300% with a strainer. When the sampling intake is modified with multiple sampling tubes and fitted with a wing to provide lift (winged arm sampler intake), the accuracy of sampling improves substantially. With this modification, the differences between sampled and feed suspended sediment concentration were more consistent and the sampled to feed concentration ratio was accurate to within 10% for particle sizes up to 250 μm.

Study of the Mechanisms of Dust Suspension Generation in a Closed Vessel Under Microgravity Conditions

An experimental method has been developed to investigate the mechanisms of dust suspension generation in a closed vessel under microgravity conditions. The objective is to characterize the evolution as function of time of the aerodynamic flow field and the dust distribution inside the vessel, in particle concentration conditions representative of actual dust explosions. Cornstarch suspensions in air have been chosen for this purpose. Special adaptation of high frame rate video records with laser sheet tomography allowed performing PIV measurements under microgravity conditions, in the unsteady flow generated during the dispersion process. It was demonstrated that cornstarch particles, in spite of their relatively large size, were suitable to be used as tracers for PIV measurements. Video registrations, at high frame rate (5,000 fps) at discrete instants in the time interval 0–10 s, of the dispersion of cornstarch particles under microgravity conditions allowed to explore the time interval 600 ms to 10 s for which there were no experimental data until now. It appears that after 500 ms, velocity and rms velocity fields become similar for g = 0 and g = 1. For characteristic times beyond 7–8 s, these fields evolve very slowly. Recordings at slower frame rate (125 fps) continuously during the whole process, showed the tendency of particles to become uniformly distributed in the vessel. The variations of particle concentration were followed using the signal of light intensity diffused by the particles. Large fluctuations of the diffused light are detected during the dispersion process. However, for g = 0, the average value of the diffused light intensity remains quasi-constant as function of time, whereas for g = 1, it decreases quickly until approximately 4 s, and then decreases much slowly and becomes slightly smaller than in the case g = 0. To get further information about the subsequent evolution of the suspension, observation of the dispersion process beyond 10 s should be done in future experiments.

Characterization of copper–silicon nitride composite electrocoatings

Silicon nitride particles were incorporated to electrolytic copper by co-electrodeposition in acidic sulfate bath, aiming the improvement of its mechanical resistance. Smooth deposits containing well-distributed silicon nitride particles were obtained. The current density did not show significant influence on incorporated particle volume fraction, whereas the variation of particle concentration in the bath had a more pronounced effect. The microhardness of the composite layers was higher than that of pure copper deposits obtained under the same conditions and increased with the increase of incorporated particle volume fraction. The microhardness of composites also increased with the increase of current density due to copper matrix grain refining. The composite coatings were slightly more corrosion resistant than pure copper deposits in 3.5% NaCl solutions.

Consolidation of Charged Colloids during Drying

We consider the drying of latex dispersions containing submicrometer-sized particles dispersed in water. It is well known that the consolidation of colloidal particles is influenced by a number of factors such as particle size and shape and interparticle potential. In this work, we focus on the effect of surface charge on the consolidation front. Recent experimental and theoretical investigations on the sedimentation of charged colloidal spheres have shown that the large mass difference between noninteracting colloids and ions sets up a macroscopic electric field, thereby enhancing the diffusivity of the particles and resulting in an inflated sedimentation profile. Our experimental measurements of the concentration profile during drying-induced consolidation also reveal similar charge effects. We present a model for the consolidation of charged particles that accounts for the presence of an induced external electric field. As expected, the predicted particle diffusivity is enhanced by the onset of the electric field at low particle concentration. Fluorescence and bright-field microscopy were used to detect the particle concentration variation in a dispersion dried in a capillary, and the measured profile agrees with the prediction confirming the influence of particle charge on consolidation.

Design and Performance Test of Comb-Shaped Clamp/Spacer for Improvement of Recirculation Filter Efficacy in a Hard Disk Drive

With the recent increase of the rotational speed of hard disk drives, nanoparticle contamination can cause serious problems including thermal asperity. We designed a comb-shaped clamp and spacer to improve the efficacy of the recirculation filter in the operation of the hard disk drive (HDD). We calculated flow characteristics by a commercial computational fluid dynamics (CFD) code for six cases of the comb-shaped clamp and spacer. The calculation results showed that the outward velocity was the highest when the comb-shape angle was 45deg. We measured temporal variations of particle concentration during the operation of the HDD by experiments. Considering the decay rate and the percent clean-up of particle concentration, we found the case of 45deg to be the best design.

Variation of particle concentrations and environmental noise on the urban neighbourhood scale

Particulate air pollution and environmental noise received increased attention within the environmental health community during recent years due to their potential impacts on human health. In this study the spatio-temporal variation of noise and particles was estimated by a short set of mobile measurements within an urban neighbourhood in Essen, Germany. Particle concentrations (PM 1 and PM coarse = PM 10 − PM 1) were measured by an optical particle counter continuously along the measurement route while environmental noise was measured at fixed points on the same route. Additionally, wind and turbulence parameters were gathered above rooftop height and within an urban street canyon. The spatial distribution of noise was very homogeneous while the distribution of particle concentrations turned out to be rather inhomogeneous. The spatial correlation between noise and particles was found to be poor for PM coarse during all measurements. However, for PM 1 and noise a moderate positive correlation ( r ∼ 0.5) emerged under conditions of weak turbulent atmospheric mixing. The spatio-temporal covariation between particles and noise is believed to be more evident for ultrafine (<100 nm) particles.

Generation of Airborne Particles from Different Bedding Materials Used for Horse Keeping

Among other factors (eg, feed), bedding material has an important effect on stable air quality with respect to airborne particle formation. This study was designed to establish which material is suited to create an improved stable environment for horses. First, the following materials were analyzed under standardized conditions in a laboratory experiment: wheat straw, dry wood shavings, hemp shives, linen shives, wheat straw pellets, paper cuttings (unprinted newspaper). The second investigation was carried out under in situ conditions in which three of these bedding materials (wheat straw, wood shavings, and straw pellets) were analyzed under practical conditions. In both experiments, airborne particle concentrations were detected online with the gravimetrically measuring analyzer TEOM 1400a (Rupprecht & Patashnick Co., Franklin, MA). In the laboratory experiment, the TEOM was equipped successively with different inlets to measure the particle fractions PM 1, PM 2.5, PM 10, and PM 20. During the in situ experiment, only the fraction PM 10 was detected. In the laboratory experiment, hemp and linen had the highest generation of airborne particles in all fractions. The lowest particle generation was detected with straw pellets. Results of the in situ investigation supported results of the laboratory experiment with respect to mean particle generation of straw pellets. With an average of 111.2 ± 149.2 μg/m 3, it was significantly lower than the mean particle generation of wheat straw with 227.5 ± 280.8 μg/m 3. The particle generation of wood shavings had an average of 140.9 ± 141.9 μg/m 3 and also was significantly lower than the generation by wheat straw. An activity-correlated variation of particle concentrations was found. In conclusion, taking both experiments into consideration, straw pellets seemed to be suitable for horse stables, to promote an improvement in the stable climate in relation to airborne particle formation.

The Transport and Deposition of Pyroclastic Material from the 1000 AD Caldera-Forming Eruption of Volcan Ceboruco, Nayarit, Mexico

The complex eruption sequence from the ∼1000 A.D. caldera-forming eruption of Volcan Ceboruco, known as the Jala Pumice, offers an exceptional opportunity to examine how pyroclastic material is transported and deposited from pyroclastic density currents over variable topography. Three main pyroclastic surge deposits (S1, S2, and S3) and two pyroclastic flow deposits (Marquesado and North-Flank PFDs) were emplaced during this eruption. Pyroclastic surge deposits are massive, planar, or cross-bedded, poor-to-well sorted, and display fluctuations in thickness, median diameter, sorting, and lithology as a function of distance, topography, and flow dynamics. Marquesado pyroclastic flow deposits reveal lateral variations from massive, poorly sorted deposits located within 5 km of Ceboruco to planar bedded, moderately well sorted deposits located >15 km away over the nearly horizontal topography to the south of Ceboruco. North-Flank pyroclastic flow deposits also reveal lateral variations from massive, poorly sorted deposits located within 4 km of Ceboruco to planar bedded, moderately well sorted deposits located 8 km away atop an escarpment that steeply rises 230 m from the northern valley floor. Field observations, granulometric analyses, component analyses, and crystal sedimentation calculations along flow-parallel sampling transects all suggest that both surges and flows were density stratified currents, where deposition occurred from a basal region of higher particle concentration that was supplied from an overlying dilute layer that transports particles in suspension. This supports the idea of a transition between “flow” and “surge” end members with variations in particle concentration. Topography greatly affects the transport and depositional capacity of the pyroclastic density currents as a result of “blocking”, either by topographic obstacles or by abrupt breaks at the base of volcano slopes, whereas the origin of Jala Pumice surge deposits (phreatomagmatic versus magmatic) appears to have little impact on their flow dynamics.

A long-term experimental study of the Saharan dust presence in West Africa

The size distribution characteristics of the Saharan dust that is transported and deposited over many countries in the West African atmospheric environment (5°N) during the months of November to March, known locally as the Harmattan, have been determined over a 9-year period between 1996 and 2005, using a location in central Ghana (6° 40′N, 1° 34′W) as the reference geographical point. The particle size distributions and concentrations are discussed. Within the particle size range measured, the average inter-annual mass concentrations during the winter months ranged from 140 μg m − 3 to 1200 μg m − 3 while the average number concentrations varied between 24 cm − 3 and 63 cm − 3 . The measured particle concentrations outside the winter period were consistently less than 10 cm − 3 . The ground-based particle measuring equipment used did not provide for distinguishing the smoke fraction (due to bush fires and biomass burning) from the Saharan dust. These values therefore correspond to the total dust loads. The size range covered by the particle counter was 0.5 μm–25 μm. In spite of the strong daily and inter-annual variations in particle concentration, the overall dust mean particle diameter over the 9-year period was found to be 1.5 μm. The particle size distributions exhibited the typical distribution pattern for atmospheric aerosols with a coarse mode diameter situated at about 3.5 μm. The control exerted on the dust incursions and the particle concentrations by both the Inter-Tropical Convergence Zone (ITCZ) and the North Atlantic Oscillation (NAO) are highlighted. The experimental results reported in this study will be of value in validating satellite based observations and simulation models of the African dust plume during winter.

Concentrations of Particulate Matter in Schools in Southwest Germany

During the winter season 2005/2006, measurements of small particulate matter were taken in 22 schools in southwest Germany. PM2.5 was measured gravimetrically. Laser particle counter (LPC) and condensation particle counter (CPC) were used to determine different particle fractions. The investigation included measurements inside (in classrooms) and outside of school buildings. During the whole investigation period continuous reference measurements were taken near the State Health Office in the city of Stuttgart. Information on building-specific data and traffic near the schools was collected via questionnaire. Although distances between the different schools and the location of the State Health Office building in Stuttgart in some cases exceeded 100 km, the concentration levels of particles > 0.3 μm measured by LPC near the different schools were similar to those measured in Stuttgart. The differences between the measurements in Stuttgart and at the other locations were smaller than the variation in time. In the winter season, the impaction of particulate matter was strongly influenced by specific weather conditions. Time resolution of measurements in classrooms showed variation in particle concentration depending on the type of building and indoor activities like cleaning or moving during breaks. Concentrations of very small particles in buildings and in ambient air measured by CPC were influenced by traffic emissions. The observed data give reason to assume that the influence of high traffic emissions to indoor particle concentration may have been overestimated. Furthermore, there is an urgent need for standardization of measurement protocols, sampling, and determination of indoor particulate matter. The classical gravimetric methods are less appropriate since they do not allow for a time resolution of measurements.

Simulation Assisted Measurement of Nanoparticle Concentration Generated during High-Density Plasma CVD of Poly-Silicon Films

To study nanoparticles generated within the high-density plasma system, it is necessary to know the particle concentration (#/cm3), which is typically measured using laser light scattering of particles trapped inside the plasma. This technique has limitations because particles are localized due to the forces that act on the trapped particles inside the plasma and the localization point varies as the particles grow. Unless spatially averaged particle concentrations are obtained by scanning through the plasma, laser light scattering measurements of particle concentration might represent only the local variation of particle concentration. In this paper, novel method is presented to measure the particle concentration employing TEM measurement results and the simulation of particle transport for calculation of transport efficiency from the plasma region where the particles are generated to the TEM grid. As the particles were collected on the TEM grid after the plasma was extinguished, the simulation includes the effects of Brownian diffusion, aerodynamic drag and gravitational sedimentation but not electrostatic or ion drag force. Simulation results were obtained for particles ranging from 5 to 100 nm. For each particle size, transport efficiencies from 56 different starting positions were evaluated. It was found that transport efficiencies of particles in the 20 to 50 nm diameter range were highest, since these particles tend to follow the gas flow. Sampling efficiencies of particles smaller than this decreased due to Brownian diffusion. For larger particles, sampling efficiencies also decreased, due to gravitational sedimentation. The measured particle concentrations were found to be ~108 #/cm3 and roughly constant over time.

Synthesis of Fe3O4/PMMA composite latex particles: Kinetic modeling

AbstractIn this work, a generalized mathematical model was developed to estimate the variation of particle concentration during the entire course of soapless emulsion polymerization of methyl methacrylate with ferrofluid. Two mechanisms for the nucleation and growth of particles throughout the polymerization reaction were discussed: Mechanism I – seeded polymerization; and Mechanism II – self‐nucleation polymerization. Here, the self‐nucleation included homogeneous nucleation and micelle nucleation. Coagulation between particles, which came from different nucleation mechanisms during the course of polymerization, was considered and included in this model. When appropriate parameters were selected, this model could be successfully used to interpret the variation of particle concentration during the entire reaction. Under different conditions, rate of polymerization, number of radicals in each particle, average molecular weight of polymers, and rate constant of termination were also calculated. All of them explained the experimental results quite well. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4925–4934, 2006

Experimental study of environmental tobacco smoke particles under actual indoor environment

Environmental tobacco smoke (ETS) is a major source of human exposure to airborne particles. In order to provide more information necessary for human exposure investigations, the aim of the work presented here is to investigate experimentally the variation of the ETS particle concentration and size distribution under an actual indoor environment, in a room of 30 m 3, using human smokers. The effect of number of cigarettes and brands of cigarettes, the effect of sampling location and the effect of ventilation rates were investigated. The results indicated little difference in the geometric mean diameter (GMD) of the ETS particles from those in background air. Under a ventilation rate of 0.03 m 3/s, the concentration of the ETS particles reached a peak value at the sampling point shortly after completing the smoking process. The GMD first increased due to coagulation and diffusion deposition, and finalize decreased due to the effect of ventilation. Smoking two cigarettes at the same time would increase the initial concentration and led to an increase in GMD of the ETS particles. Two different brands of cigarette with different tar contents released ETS particles of different GMDs but similar particle concentrations. Spatial variation in particle concentration was obvious only in the first 600 s of the tests and tended to fade out subsequently. Stronger ventilation would reduce the concentration and GMD of the particles.