Minimum Collection Efficiency Research Articles

Mode analysis of atmospheric turbulence mitigation with Multi-Plane Light Conversion

Developing standard and accessible atmospheric turbulence mitigation is of paramount importance to enable laser communication network deployment. Multi-Plane Light Conversion (MPLC) [1]–[3] is proving to be an effective technique to improve coupling efficiency of a perturbated wave-front profile towards a single-mode fiber [4]–[6]. However, to date, experimental studies are restricted to a fixed number of modes. In this work, we numerically and experimentally study performance improvement of the MPLC technique and mode collection compared to direct single mode fiber coupling for several D/r0 ratio, D being the receiver aperture diameter and r0 the Fried parameter. We calculate the coupling efficiency, represented in Fig 1. Collection for SMF only is shown in Fig 1-a while the summation of the 15 first Hermite-Gaussian modes is represented in Fig 1-b. Collection for each mode for D/r0=4 is displayed in Fig 1-c. We demonstrate that 15 modes MPLC appears to be a good compromise between number of modes and complexity of the device. This configuration typically improves the collection efficiency by >7 dB in the case of strong turbulence when D/r0 >4. More important, the minimum collection efficiency that would correspond to a link failure is dramatically increased compared to SMF fiber alone. MPLC thus shows high robustness to turbulence fluctuation.

Wind tunnel-based testing of a photoelectrochemical oxidative filter-based air purification unit in coronavirus and influenza aerosol removal and inactivation.

Recirculating air purification technologies are employed as potential means of reducing exposure to aerosol particles and airborne viruses. Toward improved testing of recirculating air purification units, we developed and applied a medium‐scale single‐pass wind tunnel test to examine the size‐dependent collection of particles and the collection and inactivation of viable bovine coronavirus (BCoV, a betacoronavirus), porcine respiratory coronavirus (PRCV, an alphacoronavirus), and influenza A virus (IAV), by a commercial air purification unit. The tested unit, the Molekule Air Mini, incorporates a MERV 16 filter as well as a photoelectrochemical oxidating layer. It was found to have a collection efficiency above 95.8% for all tested particle diameters and flow rates, with collection efficiencies above 99% for supermicrometer particles with the minimum collection efficiency for particles smaller than 100 nm. For all three tested viruses, the physical tracer‐based log reduction was near 2.0 (99% removal). Conversely, the viable virus log reductions were found to be near 4.0 for IAV, 3.0 for BCoV, and 2.5 for PRCV, suggesting additional inactivation in a virus family‐ and genus‐specific manner. In total, this work describes a suite of test methods which can be used to rigorously evaluate the efficacy of recirculating air purification technologies.

Minimum Collection Efficiency Diameter during Snow Scavenging Process

The scavenging of atmospheric aerosols by below-cloud scavenging processes during rain or snow precipitation plays an important role in the removal of aerosols in the atmosphere. Because of a variety of frozen precipitation types and their physical properties, the snow scavenging is a more complicated process compared with the rain scavenging. This study determined the minimum collection efficiency and minimum collection efficiency diameter for polydispersed hydrometeor size distributions during the snow precipitation. Three types of collectors (graupel, dendrite, and column) were considered and the obtained minimum collection efficiency and the corresponding minimum collection efficiency diameter were intercompared. Results showed that the minimum collection efficiency diameters for snow were smaller than those for rain. The minimum collection efficiency diameters of graupel decreased as the collector diameter increased, whereas other collectors (i.e., dendrite and column) did not show this decreasing tendency. The minimum collection efficiencies of graupels were larger than those of dendrite and column collectors. It was also shown that column collectors had the largest scavenging coefficients.

Radiative Forcing Associated with Particulate Carbon Emissions Resulting from the Use of Mercury Control Technology

Injection of powdered activated carbon (PAC) adsorbents into the flue gas of coal fired power plants with electrostatic precipitators (ESPs) is the most mature technology to control mercury emissions for coal combustion. However, the PAC itself can penetrate ESPs to emit into the atmosphere. These emitted PACs have similar size and optical properties to submicron black carbon (BC) and thus could increase BC radiative forcing unintentionally. The present paper estimates, for the first time, the potential emission of PAC together with their climate forcing. The global average maximum potential emissions of PAC is 98.4 Gg/yr for the year 2030, arising from the assumed adoption of the maximum potential PAC injection technology, the minimum collection efficiency, and the maximum PAC injection rate. These emissions cause a global warming of 2.10 mW m(-2) at the top of atmosphere and a cooling of -2.96 mW m(-2) at the surface. This warming represents about 2% of the warming that is caused by BC from direct fossil fuel burning and 0.86% of the warming associated with CO2 emissions from coal burning in power plants. Its warming is 8 times more efficient than the emitted CO2 as measured by the 20-year-integrated radiative forcing per unit of carbon input (the 20-year Global Warming Potential).

Preparation of electrospun polyurethane filter media and their collection mechanisms for ultrafine particles

Electrospinning is a simple and versatile process to produce polymer nanofibers, which are useful for ultrafine particle filtration. In this study, a polyurethane filter with an average fiber diameter of 150–250 nm was prepared through the electrospinning process and its filtration characteristics were investigated. We found that the electrospun fiber diameter was highly dependent on the polyurethane concentration, electric field, and tip-to-collector distance. As the polyurethane concentration, electric field, and tip-to-collector distance under the same electric field increased, the fiber diameter increased. We also found that the produced filter media had a minimum collection efficiency at particles sizes from 80 to 100 nm, which implies an electrostatic attraction between the filter and the test particles. Furthermore, we observed that interception was a predominant collection mechanism at Peclet numbers higher than 10 in nanofiber filtration for ultrafine particles. Implications: A polyurethane nanofiber filter with excellent mechanical properties was prepared, and the effect of operating conditions on fiber morphology was examined. The filter fabricated by an electrospinning process is charged and has high filtration efficiency due to electrostatic force. Therefore, it can be a good alternative to control hazardous ultrafine particles.

The influence of electric charge on minimum particle scavenging efficiency particle size during below-cloud scavenging processes

Below-cloud wet deposition scavenging processes are important for removing coarse and very fine particles from the atmosphere. This study investigated the influence of electric charge on particle deposition and estimated the scavenging gap particle size (the most penetrating particle size) along with the corresponding minimum collection efficiency and minimum scavenging coefficient particle size by using equations for below-cloud scavenging processes. A harmonic mean type approximation was used for calculations and the Cunningham correction factor was applied to include the slip effect of nuclei mode particles. Results based on the analytically approximated solution compared well with the numerically calculated results and previous studies that did not consider electric charging effects. The results showed that charge effects play an important role in determining the most penetrating particle size. This study also showed that use of the Cunningham correction factor may increase the most penetrating particle size under certain conditions. Subsequently, these results indicate that consideration of the electric charge effect with a Cunningham correction factor is important for estimating the most penetrating particle size.

Theoretical study for the most penetrating particle size of dust-loaded fiber filters

This study obtained the most penetrating particle size of dust-loaded fiber filters for polydispersed aerosol. The enhancement factor (λ) introduced by Kanaoka et al. [4] was generalized for different interception parameter and by using the simplified generalized formula, the most penetrating particle size and minimum collection efficiency for dust loaded filters was estimated. The most penetrating particle size decreases as flow velocity increases, which means that the most penetrating particle size shifts to a smaller size as flow velocity increases. This tendency is stronger for filters with dust-loaded particles than for clean filters. In addition, the results showed that the minimum collection efficiency increases as dust loading increases. The increased enhancement factor increases the interception parameter and reduces the most penetrating particle size.Further, this study calculated the most penetrating particle size of dust-loaded fiber filters by using the generalized enhancement factor obtained under the assumption of the linear approximation of the coefficient regarding the interception parameter.

Minimum Collection Efficiency Particle Diameter during Precipitation as a Function of Rain Intensity

This study found that the minimum collection efficiency particle diameter during precipitation is a function of rain intensity. The raindrop size distribution was parameterized with a log normal size distribution as a function of rain intensity, and the minimum collection efficiency and minimum collection efficiency diameter were obtained analytically.The results show that, during precipitation, both the minimum scavenging coefficient diameter and the minimum scavenging coefficient increase along with rain intensity. A comparison of the minimum collection efficiency diameters for various falling velocities reveals that there is not much of a difference in the diameters.Both the numerical and analytical results of this study agree well, without much loss of accuracy.

A Review of Termo- and Diffusio-Phoresis in the Atmospheric Aerosol Scavenging Process. Part 1: Drop Scavenging

The role of phoretic forces in providing in-cloud and below-cloud scavenging due to falling drop is reviewed by considering published papers dealing with theoretical models, laboratory and field measurements. Theoretical analyses agree that Brownian diffusion appears to dominate drop scavenging of aerosol with radius less than 0.1 μm, and inertial impaction dominates scavenging of aerosol with radius higher than 1 μm. Thus, there is a minimum collection efficiency for particles in the approximate range 0.1 μm - 1 μm, where phoretic forces are felt. Generally speaking, published papers report not uniform evaluations of the contribution of thermo- and diffusiophoretic forces. This disagreement is partially due to the different laboratory and field conditions, and different theoretical approaches.

Filtration Characteristics of Fine Particulate Matters in a PTFE/Glass Composite Bag Filter

Bag houses are often used to control particulate matters and recover valuable resources in various industries. A bag filter is the most important component in a bag house system, and thus it is important to develop the best-quality filter media and determine the optimum operating conditions of a bag house system. This study focused on particle penetrations under an operating condition of a bag house system, and investigated the relationship between dust clogging and dust penetration as a function of pressure drops across the filter medium. The results showed a minimum collection efficiency of 80% for 0.45 μm particles at the initial stage of filtration, although this quickly recovered and remained over 99.99% with a pressure drop greater than 20 mmH2O with a newly developed porous filter (air permeability = 5.78 × 10^(−11) m^2). Furthermore, the recovery time depended strongly on particle size. While it was inversely proportional to the particle size at the initial stage of filtration, it showed no difference for particles larger than 0.725 μm due to its uniform dust cake as filter cleaning proceeded.

Approximated solution on the properties of the scavenging gap during precipitation using harmonic mean method

Wet deposition refers to both natural and artificial processes where particles are scavenged by atmospheric hydrometeors. Below-cloud atmospheric particles are removed by raindrops via Brownian diffusion, interception, and impaction. The overall scavenging coefficient has a broad and distinctive minimum for aerosol penetration between 0.1 and several micrometers in diameter. In this study, the approximated analytical solution for most penetrating particle size during precipitation was obtained. Brownian diffusion and interception were considered under the assumption of the inertial impaction can be neglected in this study conditions. Both the minimum collection efficiency and minimum scavenging coefficient particle size were estimated using the harmonic mean type approximation, with the solution compared to the numerically calculated results. The approximated results were comparable with the numerical solutions. The results showed that collection efficiency diameter is a function of terminal velocity and the collection mechanisms included. When considering Brownian diffusion and interception, most penetrating particle size increases as drop diameter increases, which shows a contrary to the study of Wang (1978) and this shows that most penetrating particle size depends on collection efficiency mechanism, flow velocity and collector diameter. Consequently, this study analytically approximated general type-solutions for scavenging gap particle size and minimum collection efficiency during precipitation.

분무탑식 스크러버에서 이류체 정전분무에 의한 집진효율의 향상

There have been a number of efforts to satisfy national emission regulations and reduce the amount of emitted air pollutants. There are several air pollution control devices, however, only wet scrubber is efficiently used to remove particulate matters and gaseous pollutants, even if it has minimum collection efficiency in the particle size range of <TEX>$0.1{\sim}1{\mu}m$</TEX>. This study aimed to improve the collection efficiency of a spray tower type scrubber by introducing an electrospray system with two-flow nozzle. We found that the collection efficiency of a spray tower type scrubber was similar to that of a conventional wet scrubber. However, installation of an electrospray system in the scrubber resulted in drastic further improvement of collection efficiency comparing to that of a conventional scrubber, which is 26%, 35.2%, and 45.1% at the liquid to gas ratio of 0.26 <TEX>$L/m^3$</TEX> and 19.9%, 35.1%, and 42.5% at 0.34 <TEX>$L/m^3$</TEX> for the applied voltage of -30 kV, -35 kV, and -40 kV, respectively. Therefore, we found that the introduction of an electrospray system is very effective to improve the collection efficiency of a spray tower type scrubber.

Case Studies of Air Filtration at Microscales: Micro- and Nanofiber Media

In this work, 3–D fibrous geometries are developed to resemble the microstructure of spun-bonded and electrospun filters media and used here to simulate their filtration efficiency and pressure drop. For the sake of simplicity, a continuum flow theory was considered to prevail for the case of spun-bonded media (microfiber media) whereas our electrospun media (nanofiber media) were assumed to be in a free molecular flow regime. Our simulations results are in good general agreement with the experimental data. Especially, in predicting media's pressure drop, our results show better predictions when compared to some of the existing models. We also quantitatively demonstrated that by decreasing the fiber diameter, the minimum collection efficiency of the media having identical pressure drops increases. This effect is accompanied by a decrease in the particle diameter associated with these minimum efficiencies – the most penetrating particle diameter. Studying the influence of the gas temperature, we showed that filter's efficiency increases as the gas temperature increases. Conversely, the filter's pressure drop decreases by increasing the gas temperature.

Approximated Solution for The Most Penetrating Particle Size in Multiple Fluid Sphere Systems

There exists an intermediate size of particles, normally refereed to as most penetrating particle size, at which particles are least influenced by any collection mechanisms. The maximum aerosol penetration regime can occur where Brownian diffusion plus either gravitation or interception are the operant controlling mechanisms. In this study, a simplified approximated solution was obtained with regard to the most penetrating particle size in multiple fluid sphere systems. The harmonic mean type solution was approximated, and the results were then compared with the numerical solutions. Finally, minimum collection efficiency was calculated from the obtained solution for the most penetrating particle size. The simplified approximated solution is very consistent with the numerically calculated solution, for solid, bubble, and liquid fluid sphere systems. Consequently, this study showed that the general type-solutions were analytically approximated for both most penetrating particle size and minimum collection efficiency in multiple fluid spheres systems.

A simulation of unsteady-state filtration via nanofiber media at reduced operating pressures

In this work, 3-D structures resembling nanofiber ( d f < 200 nm ) filter media are simulated and challenged with nanoparticle aerosols at reduced operating pressures. For the range of fiber diameters considered in this paper, the free molecular flow regime is dominant. Therefore, the disturbances to the air flow field caused by the fibers are neglected. Nanoparticle capture efficiency of nanofiber webs, due to Brownian diffusion and interception, is calculated for particle diameters ranging from 50 to 500 nm. Our simulations show that by decreasing the fiber diameter, the minimum collection efficiency of filtration media having identical pressure drops increases. This effect is accompanied by a decrease in the particle diameter associated with these minimum efficiencies—the most penetrating particle diameter. Moreover, it is demonstrated that increasing the flow temperature enhances the nanoparticle capture efficiency of nanofiber filters. Allowing the particles to deposit on the fibers as well as each other, the caking process of such nanofiber filters is simulated for different monodisperse and polydisperse aerosols at different temperatures. The statistical information regarding the composition of nanoparticle cakes formed at high and low temperatures is presented and discussed.

Analytic Solution on Critical Suspended Particle Size and Minimum Collection Efficiency in Deep Bed Filtration

Deep bed filtration is one of the most frequently employed water treatment techniques, and is routinely applied in the clarification of dilute particle suspensions. The prediction of critical suspended particle size is important due to the fact that the corresponding minimum collection efficiency is one of the primary considerations in the design of facilities based on filtration mechanisms. In this study, critical suspended particle size was studied analytically for the case of the Rajagopalan and Tien (RT) filtration model using a harmonic mean type of approximation, as well as a calculation of minimum collection efficiency. The obtained analytic solutions were then compared with the experimental and numerically calculated results, showing good agreement. This analytic solution for critical suspended particle size appears to be applicable to the determination of optimal conditions in deep-bed filtration protocols.

Characteristics of Inhalable Particulate Matter Concentration and Size Distribution from Power Plants in China

In this investigation, the collection efficiency of particulate emission control devices (PECDs), particulate matter (PM) emissions, and PM size distribution were determined experimentally at the inlet and outlet of PECDs at five coal-fired power plants. Different boilers, coals, and PECDs are used in these power plants. Measurement in situ was performed by an electrical low-pressure impactor with a sampling system, which consisted of an isokinetic sampler probe, precut cyclone, and two-stage dilution system with a sample line to the instruments. The size distribution was measured over a range from 0.03 to 10 µm. Before and after all of the PECDs, the particle number size distributions display a bimodal distribution. The PM2.5 fraction emitted to atmosphere includes a significant amount of the mass from the coarse particle mode. The controlled and uncontrolled emission factors of total PM, inhalable PM (PM10), and fine PM P(M2.5) were obtained. Electrostatic precipitator (ESP) and baghouse total collection efficiencies are 96.38–99.89% and 99.94%, respectively. The minimum collection efficiency of the ESP and the baghouse both appear in the particle size range of 0.1–1 µm. In this size range, ESP and baghouse collection efficiencies are 85.79–98.6% and 99.54%. Real-time measurement shows that the mass and number concentration of PM10 will be greatly affected by the operating conditions of the PECDs. The number of emitted particles increases with increasing boiler load level because of higher combustion temperature. During test run periods, the data reproducibility is satisfactory.

Wet scrubbing of polydisperse aerosols by freely falling droplets

In this study, analytical solutions for removal of a polydisperse aerosol by wet scrubbing were derived employing Brownian diffusion and inertial impaction as removal mechanisms. Size distribution of aerosol particles were assumed to be represented by a time-evolving log-normal function during the scrubbing process. Derived solutions were compared with the direct integration solution, which is not based on the log-normal assumption, showing good agreement. Error resulting from the log-normal assumption was shown to be greater in the impaction-dominant regime than in the diffusion-dominant regime due to higher size dependency of collision kernel which destructed log-normal shape of size distribution. The monodisperse model significantly overpredicted particle removal in the diffusion- and impaction-dominant size regimes due to its incapability of tracing average particle size change, while it underpredicted particle removal in the intermediate size range because of neglect of polydispersity effect. A new solution for the minimum collection efficiency particle diameter was also provided. The minimum efficiency diameter was shown not to be very sensitive to the scrubbing condition and to lie around 0.3 μ m for wide range of size and concentration of water drops.

Effect of the Energy Barrier of DLVO Theory on the Deposition of Brownian Particles in Porous Media Using the Constricted Tube Model

The deposition problem of colloidal particles in porous media is investigated theoretically by using the Brownian dynamics simulation method. The pore structure was characterized by the constricted tube model, and the effects of the particle size and the total interaction energy curve of the DLVO theory of various shapes on the collection efficiencies of particles are examined. The simulation results show that: (1) a particle size with a minimum collection efficiency exists when the value of Reynolds number is small, and (2) the dimensionless groups, NE1, NE2, NDL, and NLO which characterize the height of the primary maximum and the depth of the secondary minimum in the total interaction energy curve play a major role in determining the collection efficiencies of Brownian particles with low Reynolds numbers. numbers. In addition, when comparing the present model with the available experimental data (Bai and tien, 1999), it is found that the simulation results obtained from the present model coincide more closely with the experimental data than that of the convective diffusion model in the unfavorable deposition region.

Analytic solution for polydispersed aerosol dynamics by a wet removal process

An analytic solution for polydispersed aerosol dynamics by wet deposition of droplets was obtained. The collection efficiency used was based on the results of Jung and Lee (Aerosol Sci. Technol. 29 (1998) 389). The derived efficiency was compared with the existing formula of Slinn (Atmospheric Science and Power Production—1979, Division of Biomedical Environmental Research, U.S. Department of Energy, Washington DC, USA, 1983 (Chapter 11)) and showed good agreement. The particle size distribution was assumed to have a log-normal function, and the Cunningham slip correction factor was simplified to introduce the moment relationship. Both analytic and numerical solutions were obtained and compared with each other. The results show that the analytic solution can simulate the scavenging of polydispersed aerosol by wet deposition for the diffusion-dominant range well. The particle diameter of minimum collection efficiency was obtained analytically. It was found that the minimum collection efficiency diameter increases with decreasing velocity and decreasing packing density.