Decrease In Number Concentration Research Articles

Promotion of particle agglomeration by different vortex generator angles based on PIV-PDPA experiment

Turbulent agglomeration is a promising pretreatment technology aimed at enhancing fine particles removal efficiency. Recent studies suggested that V-structure vortex generators are effective in improving turbulence to promote particle collisions and size increase. However, the experimental studies on flow fields and particles induced by V-structure vortex generators with different angles are still insufficient. To this end, this study investigated the effect of the angle of V-structure vortex generators on particle agglomeration based on the experimental approach. More specifically, the flow field dynamics were obtained directly from a Particle Image Velocimetry, while the particle behavior and size variation were investigated by a Phase Doppler Particle Analyzer. The results of the Phase Doppler Particle Analyzer showed that the addition of the vortex generator and its angle increase led to an increase in average size as well as cross-particle size, while a decrease in number concentration of smaller particles, which confirmed the collisions between smaller particles. Through Particle Image Velocimetry experiments, it was found that a wider range of recirculation regions and counter-rotating eddies were generated. Furthermore, by analyzing particle distribution and tracking single particle trajectory through numerical simulation, two kinds of agglomeration mechanisms were proposed. One being the trajectory crossover of smaller particles triggered by recirculating vortex, and the other is the preferential concentration of larger particles. The results of this study can provide a theoretical basis for the design of V-structure vortex generators and particle agglomeration techniques.

What Are the Similarities and Differences in Marine Boundary Layer Cloud and Drizzle Microphysical Properties During the ACE‐ENA and MARCUS Field Campaigns?

AbstractThis study compares macrophysical and microphysical properties of single‐layered, liquid‐dominant MBL clouds from the Measurements of Aerosols, Radiation, and Clouds over the Southern Ocean (MARCUS) (above 60°S) and the ARM East North Atlantic (ENA) site during the Aerosol and Cloud Experiments in Eastern North Atlantic (ACE‐ENA) field campaign. A total of 1,136 (16.5% of clouds) and 6,034 5‐min cloud samples are selected from MARCUS and ARM ENA in this study. MARCUS clouds have higher cloud‐top heights, thicker cloud layers, larger liquid water path, and colder cloud temperatures than ENA. Thinner, warmer MBL clouds at ENA can contain higher layer‐mean liquid water content due to higher cloud and ocean surface temperatures along with greater precipitable water vapor (PWV). MARCUS has a higher drizzle frequency rate (71.8%) than ENA (45.1%). Retrieved cloud and drizzle microphysical properties from each field campaign show key differences. MARCUS clouds feature smaller cloud droplets, whereas ENA clouds have larger cloud droplets, especially at the upper region of the cloud. From cloud top to cloud base, drizzle drop sizes increase while number concentrations decrease. Drizzle drop radius and number concentration decrease from cloud base to drizzle base due to net evaporation, and MARCUS' lower specific humidity leads to a higher drizzle base than ENA. The broader surface pressure and lower tropospheric stability (LTS) distributions during MARCUS have demonstrated that there are different synoptic patterns for selected cases during MARCUS with less PWV, while ENA is dominated by high pressure systems with nearly doubled PWV.

Apportionment of the Pre‐Industrial to Present‐Day Climate Forcing by Methane Using UKESM1: The Role of the Cloud Radiative Effect

AbstractThe Year 1850 to 2014 increase in methane from 808 to 1831 ppb leads to an effective radiative forcing (ERF) of 0.97 ± 0.04 W m−2 in the United Kingdom's Earth System Model, UKESM1. The direct methane contribution is 0.54 ± 0.04 W m−2. It is better represented in UKESM1 than in its predecessor model HadGEM2 due to shortwave and longwave absorption improvements and the absence of an anomalous dust response in the UKESM1 simulations. An indirect ozone ERF of 0.13–0.20 W m−2 is due to the tropospheric ozone increase outweighing that of the stratospheric decrease. The indirect water vapor ERF of 0.02–0.07 W m−2 is consistent with previous estimates. The methane increase also leads to a cloud radiative effect of 0.12 ± 0.02 W m−2 from thermodynamic adjustments and aerosol‐cloud interactions (aci). Shortwave and longwave contributions of 0.23 and −0.35 W m−2 to the cloud forcing arise from radiative heating and stabilization of the upper troposphere, reducing convection and global cloud cover. The aerosol‐mediated contribution (0.28–0.30 W m−2) is due to changes in oxidants reducing new particle formation (−8%), shifting the aerosol size distribution toward fewer but larger particles. Cloud droplet number concentration decreases and cloud droplet effective radius increases. This reduction in the Twomey effect switches the cloud forcing sign (−0.14 to 0.12 W m−2) and is due to chemistry‐aerosol‐cloud coupling in UKESM1. Despite uncertainties in rapid adjustments and process representation in models, these results highlight the potential importance of chemistry‐aerosol‐cloud interactions and dynamical adjustments in climate forcing.

Correlation analysis of mechanical and state characteristics of diesel engine exhaust particles

AbstractAiming at the influence of diesel engine exhaust particle mechanical characteristics on the state characteristics, studies were carried out using atomic force microscopy, high‐resolution transmission electron microscopy, and x‐ray small‐angle scattering. The variation rules of cluster‐particle interaction force and state characteristic parameters such as particle morphology and spatial structure were discussed. According to the principle of normalization, the relationship between the mechanical and state characteristics of the particles is analyzed. The results show that as the particle size increases in the exhaust process, the attractive force Fat, adhesion Fad, and adhesion energy Wad increase between the particles, Fat from 1.27 to 1.58 nN, Fad from 3.75 to 4.38 nN, Wad from 2.17 × 10−16 to 2.44 × 10−16 J. The particles are gradually agglomerated, and the cluster size is increased, indicating a certain relationship between the mechanical characteristics of the particles and the morphology. Along the exhaust direction, the particle equivalent diameter increases, and the mechanical characteristics are enhanced, while the organic matter and moisture in the exhaust are continuously adsorbed, aggravating the aggregation and shrinkage between the particles. The scattering characteristic parameters qminand qTdecrease, qminfrom 0.34 to 0.28 and qTfrom 0.72 to 0.63, the pore structure parameters decrease, the pore number concentration decreases, the peak pore size changes from 7–9 nm to 5–6 nm, the agglomerate particle structure defects decrease and the density is increased, indicating that there is a certain relationship between the mechanical characteristics of the particles and the spatial structure.

超純水中の空気ウルトラファインバブルの保存、輸送、濃縮、希釈及び除去

As ultrafine bubble (UFB) water becomes widespread in society, it is extremely important to see if the UFB water can be treated like a popular aqueous solution. The most fundamental handling includes storage, transportation, concentration, dilution and removal. Although the number concentration of UFBs gradually decreased even in an environment where it was allowed to stand at room temperature, it maintained about a few hundred million/mL for several months. There was also no significant decrease in number concentration due to the international transportation between Japan and Germany. The UFBs in water could be concentrated by vacuum evaporation method or very slow forward partial freezing method. Furthermore, UFB water could be diluted with ultrapure water. The UFB number concentration distribution hardly changed in these various concentration adjustment operations. The UFBs were removed from UFB water by ultrasonic irradiation in the MHz band.

Coagulation and capture of fine particles in the coupling system of corona discharge and embedded turbulence

Fine particles with the size below 1 μm are difficult to be captured with the traditional dust removal devices because of their poor charge capacity and filterability. Using the agglomeration pretreatment can realize the fine particles growth, then facilitating the capture process. In this study, a novel system with the combination of corona discharge and embedded turbulence was put forward. The results showed that the device can agglomerate the smaller particles into bigger ones, and the maximum decrease of number concentration for small particles can reach 40% in the bipolar corona discharge condition. The median diameters of fine particles can be improved by 47% maximumly in the condition of arrangement of turbulence bars and loopholes with a lower flow velocity. The simulated calculation and pilot scale test were conducted and the results were consistent with experimental conclusions.

Trends in primary and secondary particle number concentrations in urban and regional environments in NE Spain

We analysed long-term datasets of ambient air concentrations of gaseous pollutants, black carbon (BC) and particle size distributions at an urban background air quality station (Barcelona, Spain; 2013–2019) and a regional background station (Montseny, Spain; 2014–2019). Using BC as a tracer of primary emissions, we segregated the aerosol load in modes and analysed their trends, considering all-year data and seasons separately. We also applied the positive matrix factorisation (PMF) receptor model to the particle size distributions to identify different sources that contribute to the particle number concentration. Our results show that the number concentration of primary particles decreased at the urban and regional background stations (−4.1 and −4.7% per year, respectively) along the period of study. This decrease was also observed for primary particles in the nucleation, Aitken and accumulation modes separately. This change leads to a decrease in condensation sinks (CS, −3.1 and −5.6% per year), that, together with an increase in temperatures (+1.5% per year in the urban background; +1.4% per year in the regional background), results in a markedly increasing trend in the contribution of new particle formation to the total number particle concentration (+17.7% and +11.9% per year). The total particle number concentration decreased in the urban background (−2.5% per year), whereas the trend increased for the regional background (+3.0% per year). The latter result is in contrast to most literature reports and is most likely due to higher insolation and increased biogenic VOC (BVOC) emissions that would enhance photonucleation, along with a marked decrease in the CS. An increasing trend in H2SO4 concentrations driven by increasing SO2 concentrations (+11.1% per year) could also be favouring the formation of new particles in the regional background, but it is not clear that the increasing trend in SO2 is real or it is related to a faulty maintenance of the instrumentation.Overall, we conclude that decreasing primary emissions results in a decrease in the total number concentrations of urban aerosols, despite the increase in the formation of new particles by photonucleation. Moreover, the total particle number concentration of regions downwind of the urban areas increases because new particle formation is more favoured and compensates for the primary particles’ number concentration decrease.

Turbulence Effects on Precipitation and Cloud Radiative Properties in Shallow Cumulus: an Investigation Using the WRF-LES Model Coupled with Bin Microphysics

Using the large-eddy simulation version of the Weather Research and Forecasting (WRF) model coupled with a detailed bin microphysics scheme, the effects of turbulence-induced collision enhancement (TICE) on precipitation and cloud radiative properties in shallow cumulus are investigated. Similar to previous studies, the enhanced droplet collision results in an increase in rainwater content and surface precipitation amount. However, under low aerosol number concentration, the relative frequency of large surface precipitation amount is decreased mainly due to the decreased condensation amount. Due to TICE, the mean drop size increases and the drop number concentration decreases, which results in a decrease in evaporation and hence increasing cloud fraction. However, these changes induce a decrease in cloud optical thickness which largely offsets the increased cloud fraction when the domain-averaged albedo is calculated. Similarly, a decrease in cloud top height caused by the decreased in-cloud vertical velocity largely offsets the increased cloud fraction when the domain-averaged outgoing longwave radiation is calculated. Therefore, the effects of TICE on cloud radiative properties in shallow cumulus do not appear prominently. In addition, TICE results in a decrease in the shear production of turbulent kinetic energy, which indicates that TICE acts to produce a negative feedback.

On Which Microphysical Time Scales to Use in Studies of Entrainment‐Mixing Mechanisms in Clouds

AbstractThe commonly used time scales in entrainment‐mixing studies are examined to seek the most appropriate one, based on aircraft observations of cumulus clouds from the RACORO campaign and numerical simulations with the Explicit Mixing Parcel Model. The time scales include the following: τevap, the time for droplet complete evaporation; τphase, the time for saturation ratio deficit (S) to reach 1/e of its initial value; τsatu, the time for S to reach −0.5%; and τreact, the time for complete droplet evaporation or S to reach −0.5%. It is found that the proper time scale to use depends on the specific objectives of entrainment‐mixing studies. First, if the focus is on the variations of liquid water content (LWC) and S, then τreact for saturation, τsatu and τphase are almost equivalently appropriate, because they all represent the rate of dry air reaching saturation or of LWC decrease. Second, if one focuses on the variations of droplet size and number concentration, τreact for complete evaporation and τevap are proper because they characterize how fast droplets evaporate and whether number concentration decreases. Moreover, τreact for complete evaporation and τevap are always positively correlated with homogeneous mixing degree (ψ); thus, the two time scales, especially τevap, are recommended for developing parameterizations. However, ψ and the other time scales can be negatively, positively, or not correlated, depending on the dominant factors of the entrained air (i.e., relative humidity or aerosols). Third, all time scales are proportional to each other under certain microphysical and thermodynamic conditions.

Simulation of Particle Coagulation and Breakage in a Planar Jet via the DEMM Method

Simultaneous numerical simulation of particle coagulation and breakage in a planar jet is performed. Large eddy simulation (LES) is adopted to calculate the flow field and the direct expansion method of moments (DEMM) is employed to describe the evolution of particles undergoing coagulation and breakage. The Aggregation-Breakage Balance Equation is converted to a set of moment equations which contains the n/2th (n=0∼4) moments through the DEMM method. The newly proposed DEMM model is confirmed to be valid to describe the evolution of particle size distribution (PSD). The coherent structures dominate the evolution of particle concentration, geometric mean diameter and geometric standard deviation. The particle number concentration decreases and the span of particle diameter gets wider along the centerline as the jet develops. The geometric standard deviation is larger in the shear layer than that in the jet core.

Changes in the Ångstrom Exponent during Aerosol Coagulation and Condensation

In this study, the <TEX>${\AA}$</TEX>ngstrom exponent for polydispersed aerosol during dynamic processes was investigated. Log-normal aerosol size distribution was assumed, and a sensitivity analysis of the <TEX>${\AA}$</TEX>ngstrom exponent with regards the coagulation and condensation process was performed. The <TEX>${\AA}$</TEX>ngstrom exponent is expected to decrease because of the particle growth due to coagulation and condensation. However, it is difficult to quantify the degree of change. In order to understand quantitatively the change in the <TEX>${\AA}$</TEX>ngstrom exponent during coagulation and condensation, different real and imaginary parts of the refractive index were considered. The results show that the <TEX>${\AA}$</TEX>ngstrom exponent is sensitive to changes in size distribution and refractive index. The total number concentration decreases and the geometric mean diameter of aerosols increase during coagulation. On the while, the geometric standard deviation approaches monodispersed size distribution during the condensation process, and this change in size distribution affects the <TEX>${\AA}$</TEX>ngstrom exponent. The degree of change in the <TEX>${\AA}$</TEX>ngstrom exponent depends on the refractive index and initial size distribution, and the size parameter changes with the <TEX>${\AA}$</TEX>ngstrom exponent for a given refractive index or chemical composition; this indicates that the size distribution plays an important role in determining the <TEX>${\AA}$</TEX>ngstrom exponent as well as the chemical composition. Subsequently, this study shows how the <TEX>${\AA}$</TEX>ngstrom exponent changes quantitatively during the aerosol dynamics processes for a log-normal aerosol size distribution for different refractive indices; the results showed good agreement with the results for simple analytic size distribution solutions.

Exposure to engineered nanoparticles: Model and measurements for accident situations in laboratories

In the life cycle of engineered nanoparticles (ENP), their manufacturing requires particular attention because of unwanted potential ENP emissions to workplaces. We simulated three scenarios of equipment failure during gas phase production of nanoparticles in a laboratory. The emission plume of nanoparticles was tracked with high spatial and temporal resolution by 10 measurement devices. While under normal production conditions, no elevated ENP concentrations were observed, worst case scenarios led to homogeneous indoor ENP concentrations of up to 106cm−3 in a 300m3 production room after only 60s. The fast dispersal in the room was followed by an exponential decrease in number concentration after the emission event. Under conditions like those observed – rapid dispersal and good mixing – a single measurement device alone can provide valuable information for an ENP exposure assessment. A one-box model adequately reflected measured number concentrations (r2>0.99). The ENP emission rates to the workplace were estimated between 2.5·1011 and 6·1012s−1 for the three emission scenarios. The worst case emission rate at the production zone was also estimated at 2·1013s−1 with a stoichiometric calculation based on the precursor input, density and particle size. ENP intake fractions were 3.8–5.1·10−4 inhaled ENP per produced ENP in the investigated setting. These could only be substantially lowered by leaving the production room within a few minutes after the emission event.

Effect of ventilation in enclosure machine system on MWF aerosol properties

In this paper the influence of ventilation air velocity on properties of metal working fluids (MWF) aerosol/mist is presented. Aerosol characteristics were monitored in the chamber as well as at the entrance of ventilation pipe by optical particle size analyzer. Aerosol was generated from 6% water emulsion of three commercial MWF. Four different velocities, less than the velocity of secondary atomization, were examined (1, 3, 6, 8 m/s). Droplets size distribution, mass concentration (mg/m3), as well as number concentration (P/cm3) were measured and analyzed. From the results obtained it may be seen that coalescence is more pronounced as the velocity increases, although the number concentration decreases, due to higher air dilution. Therefore, more droplets are in a whirling motion at higher air velocities, hence more random collisions are possible. Further analysis shows that there is one value of air velocity under which the maximum difference between the aerosol in chamber and the aerosol at the entrance of the pipe can be observed. This velocity could be named specific velocity and depends on the given aerosol properties. It could be assumed that specific velocity is conditioned by the properties of oil from which emulsion is prepared. Oil viscosity and molar mass have greatest influence on the specific velocity.

Influence of cetane number improver on performance and emissions of a common-rail diesel engine fueled with biodiesel-methanol blend

In this paper, the effect of cetane number (CN) improver on performance and emissions, including particulate number concentration and size distribution, of a turbocharged, common-rail diesel engine fueled with biodiesel-methanol were studied. Two volume fractions (0.3% and 0.6%) of CN improver were added to BM30 (30% of methanol in the biodiesel-methanol blend) in the experiment. The results show that, compared with those of biodiesel-methanol blend, the peak value of cylinder pressure increases, the second peak of heat release rate decreases, the start of second heat release are advanced, and the fuel economy and thermal efficiency are improved when CN improver is added to biodiesel-methanol blend. Besides, CO and HC emissions decrease, NO x emission varies little and smoke emissions increase slightly. Moreover, exhaust particles of BM30 mainly distribute in nanosize range. Furthermore, particle number concentration decreases and peak of size distribution profile shifts toward large size direction.

Dependence between Nonvolatile Nucleation Mode Particle and Soot Number Concentrations in an EGR Equipped Heavy-Duty Diesel Engine Exhaust

Heavy duty diesel engine exhaust characteristics were studied with direct tailpipe sampling on an engine dynamometer. The exhaust particle size distributions, total particle mass, and gaseous emissions were measured with different load conditions without after-treatment. The measured particle size distributions were bimodal; distinctive accumulation and nucleation modes were detected for both volatile and dry particle samples. The condensing volatile compounds changed the characteristics of the nonvolatile nucleation mode while the soot/accumulation mode characteristics (concentration and diameter) were unchanged. A clear dependence between the soot and the nonvolatile nucleation mode number concentrations was detected. While the concentration of the soot mode decreased, the nonvolatile nucleation mode concentration increased. The soot mode number concentration decrease was related to soot-NOx trade-off; the decrease of the exhaust gas recirculation rate decreased soot emission and increased NOx emission. Simultaneously detected increase of the nonvolatile nucleation mode concentration may be caused by the decrease of the soot mode sink or by changed combustion characteristics. However, the total particle number concentration increased with decreasing soot mode number concentration. The proportion of the particle number concentration between the nonvolatile nucleation and soot mode followed the NO2:NO ratio linearly. While ratio NO2:NO increased the proportion of soot mode number concentration in total number concentration increased. Regardless of the mechanism that causes the balance between the soot mode and the nonvolatile nucleation mode emissions, the changes in the particle number size distribution should be taken into account while the particle mass emissions are controlled with combustion optimization.

On the aerosol number concentration–wind speed relationship during a severe cyclonic storm over south Indian Ocean

Measurements of the number concentration and size distribution of aerosols in the range of 0.5–20 μm diameter were made during a severe cyclonic storm in the Southern Hemisphere at 53.3°S, 52.5°E on 19 February 2004. Data were analyzed to study the aerosol number concentration–wind speed relationship. It was found that in conformity with past observations, total aerosol number concentration increases with increase in wind speed from 4 to 11 m s−1, measured at 10 m above sea level. However, contrary to most of the earlier studies, total aerosol number concentration decreases with increase in the wind speed from 16 to 22 m s−1 and then maintains an almost constant value up to the maximum wind speed of 33.1 m s−1. The total aerosol number concentration varies a little with wind speed in the range of 11–16 m s−1. While increase in the total aerosol number concentration corresponding to the increase in wind speed from 4 to 11 m s−1 is spread over the whole range of particle sizes, decrease in the aerosol number concentration associated with increase in wind speed from 16 to 22 m s−1 is mainly due to decrease in the concentration of particles of &lt;1 μm. The increase in aerosol number concentration is well recognized as being due to the enhanced bubble‐breaking activity at the sea surface and increased entrainment of sea‐salt particles, once produced. We propose that decrease in the aerosol number concentration may possibly occur because of the scavenging of aerosols by larger seawater drops injected into the atmosphere at high wind speeds. This scavenging process may act as a built‐in sink, which becomes operative at high wind speeds and restricts the enhancement in concentration of marine aerosols.

Retrieval of Cloud Properties for Partly Cloudy Imager Pixels

Abstract Retrievals of cloud properties from satellite imagery often invoke the assumption that the fields of view are overcast when cloud-contaminated, even though a significant fraction are only partially cloud-covered. The overcast assumption leads to biases in the retrieved cloud properties: cloud amounts and droplet effective radii are typically overestimated, while visible optical depths, cloud altitudes, cloud liquid water amounts, and column droplet number concentrations are typically underestimated. In order to estimate these biases, a retrieval scheme was developed to obtain the properties of clouds for partially covered imager fields of view. The partly cloudy pixel retrieval scheme is applicable to single-layered cloud systems and invokes the assumption that clouds that only partially cover a field of view are at the same altitude as nearby clouds from the same layer that completely cover imager pixels. The properties of the retrieval are illustrated through its application to 2-km Visible and Infrared Scanner (VIRS) data from the Tropical Rainfall Measuring Mission (TRMM) for a marine stratocumulus scene. The scene was chosen because the cloud properties are typical of such systems based on an analysis of VIRS data for February and March 1998. Comparisons of properties for clouds in partly cloudy pixels and those for clouds in nearby overcast pixels reveal that the optical depths and droplet effective radii are generally smaller for the clouds in the partly cloudy pixels. In addition, for pixel-scale cloud fractions between 0.2 and 0.8, optical depth, droplet effective radius, and column droplet number concentration decrease slowly with decreasing cloud cover fraction. The changes are only about 20%–30%, while cloud cover fraction changes by 80%. For comparison, changes in optical depth and column number concentration retrieved using a threshold method decrease by 80%–90%. As long as the cloud cover in partly cloudy pixels is greater than about 0.1, uncertainties in the estimates of the cloud altitudes and of the radiances for the cloud-free portions of the fields of view give rise to uncertainties in the retrieved cloud properties that are comparable to the uncertainties in the properties retrieved for overcast pixels.

One year boundary layer aerosol size distribution data from five nordic background stations

Abstract. Size distribution measurements performed at five different stations have been investigated during a one-year period between 01 June 2000 and 31 May 2001 with focus on diurnal, seasonal and geographical differences of size distribution properties. The stations involved cover a large geographical area ranging from the Finnish Lapland (67º N) down to southern Sweden (56º N) in the order Värriö, Pallas, Hyytiälä, Aspvreten and Vavihill. The shape of the size distribution is typically bimodal during winter with a larger fraction of accumulation mode particles compared to the other seasons. Highest Aitken mode concentration is found during summer and spring during the year of study. The maximum of nucleation events occur during the spring months at all stations. Nucleation events occur during other months as well, although not as frequently. Large differences were found between different categories of stations. Northerly located stations such as Pallas and Värriö presented well-separated Aitken and accumulation modes, while the two modes often overlap significantly at the two southernmost stations Vavihill and Aspvreten. A method to cluster trajectories was used to analyse the impact of long-range transport on the observed aerosol properties. Clusters of trajectories arriving from the continent were clearly associated with size distributions shifted towards the accumulation mode. This feature was more pronounced the further south the station was located. Marine- or Arctic-type clusters were associated with large variability in the nuclei size ranges. A quasi-lagrangian approach was used to investigate transport related changes in the aerosol properties. Typically, an increase in especially Aitken mode concentrations was observed when advection from the north occurs, i.e. allowing more continental influence on the aerosol when comparing the different measurement sites. When trajectory clusters arrive to the stations from SW, a gradual decrease in number concentration is experienced in all modes as latitude of measurement site increases.

Coagulation of symmetric and asymmetric bipolar aerosols

Coagulation of charged aerosols is investigated by developing a sectional numerical model for both particle size and charge distributions and accounting for electrostatic dispersion. Symmetric bipolar charging increases the coagulation rate when particles are highly charged. Asymmetric bipolar charging results in a faster decrease in the particle number concentration, but does not actually result in larger particles as the decrease in number concentration is dominated by the electrostatic dispersion and not by the coagulation of particles. The performance of a simpler model in the literature is evaluated by comparing its predictions against those of the above sectional model. The simple model is most accurate for initially mildly asymmetric bipolar aerosols at short residence times.

Bipolar charged aerosol agglomeration with alternating electric field in laminar gas flow

This paper presents the results of an experimental study for a method of increasing the efficiency of electrostatic precipitators for the collection of fly ash particles of submicron size. An alternating electric field was used to induce agglomeration of bipolarly charged particles (bipolar AC-agglomeration). A bench-scale AC-agglomeration test apparatus with bipolar corona charger was constructed. Test aerosol was generated from vegetable oil. The total mass loading was 0.2 gm −3 (5 × 106 particles cm −3), mass median diameter was 0.5 μm. Count median diameter was 0.2 μm, and geometrical standard deviation was 1.8. Residence time in the agglomerator was 4.8 s and the agglomerator field was 5.0 kV cm −1 (rms). Systematic experiments were conducted to investigate the agglomeration efficiency of the system. The percentage decrease in number concentration of 0.1–1.0 μm sized particles was found to be between 17 and 19%.