Development of a Compact Electrostatic Nanoparticle Sampler for Offline Aerosol Characterization

A compact electrostatic nanoparticle sampler has been developed to support the offline analysis of nanoparticles via electron microscopy. The basic operational principle of the sampler is to electrically charge particles by mixing nanoparticles and unipolar ions produced by DC corona discharge, and electrostatically collecting charged particles. A parametric study was first performed to identify the optimal operating condition of the sampler: a total flow rate (i.e., the sum of the particle and ion carrier flow rates) of 1.0 lpm, an aerosol/ion carrier flow rate ratio of 1.0, and a collection voltage of 4.5 kV. Under the above condition, the sampler achieved a collection efficiency of more than 90 % for particles ranging from 50 to 500 nm. The effect of particle material on the sampler’s performance was also studied. The prototype had lower collection efficiencies for oleic acid particles than for sodium chloride particles in the size range from 50 to 150 nm, while achieving a comparable efficiency in the size range large than 150 nm. Effects of particle diameter, particle material, and total flow rate on the sampler’s collection efficiency are explained by the particle charging data, i.e., charging efficiencies and average charges per particle.     

Enhancing fine particle separation by hybrid-electrostatic-turbulence coagulation: An experimental and numerical investigation

The electrostatic precipitator(ESP) has low efficiency in removing sub-micron particles. Coagulation technology, as a fine particle pretreatment technology, uses an external effect to agglomerate and grow fine particles, increase the average particle size, and make it easier to remove by subsequent dust removal equipment. However, the coagulation efficiency of a single coagulation technology is limited. Aiming at the particle charging mechanism and coagulation mechanism in the electric/turbulent composite coagulation process of fine particles, this paper uses a combination of numerical simulation and experiment to study the effects of different structural parameters, discharge parameters and flue gas parameters on corona discharge and particle charge. On this basis, the coagulation characteristics of charged particles in the turbulent flow field are studied. The results show that, when the Angle between the tip of the arista electrode is 90°, the corona discharge effect is the best. With the increase of supply voltage and temperature, the charge of particles increases. When the applied positive voltage is 29 kV and negative voltage is ?35 kV, the total coagulation coalescence efficiency of fine particles reaches the maximum. The coagulation efficiency increases with the increase of temperature, but decreases with the increase of inlet flow rate.     

Characteristic Analyses of Plasma Air Cleaning Systems for the Removal of Indoor Air Pollutants

Tobacco smoke is one of the most common manmade aerosols. Yellow sand dust and pollen are the particular and regional pollutants generated by natural phenomena. These pollutants have different removal characteristics, respectively, when the air cleaning system is operated. It is well known that tobacco smoke particles are removed effectively with electrostatic precipitators. But it is necessary to evaluate whether the plasma air cleaning system has good performance of removing Yellow sand dusts and pollens simultaneously and also to establish the operation modes for efficient removal of those particular air pollutants by controlling the air flow rates passing the electrostatic precipitator and operating times of air cleaning system. In this study, the performance evaluation of plasma air cleaning systems is investigated with tobacco smoke particles, Yellow sand dusts, and pollens. For the multi-pass test in occupied spaces of 150 m³, the operation time required to reduce dust concentration from the initial concentration of 300 µg/m³ to 150 µg/m³, the criteria of indoor air quality in Korea, are 40 min for tobacco smoke, 28 min for Yellow sand dust, and 5 min for pollen when the flow rate is 17 m³/min. Also, the optimal operation modes for each pollutant are suggested for the efficient removal of indoor air pollutants. At first, most particles are removed by maximum flow operation. Second, the rest of the particles are removed by medium flow operation. Next, the plasma air cleaning systems are maintained by minimum flow for tobacco smoke mode and by repeating minimum flow and medium flow for Yellow sand and pollen modes. Edit to “Because the Yellow sand dust and the pollen flow into the room continuously and settle down … noise reduction.” Because the Yellow sand dust and the pollen flow into the room continuously and settle down. The plasma air cleaning system is suitable for the removal of the tobacco smoke, the Yellow sand dust, and the pollen for maintaining suitable indoor air quality, and, if it is operated through the suitable operation mode, energy efficiency will improve noise reduction.     

Electrostatic collection of tribocharged lunar dust simulants

Levitation and consecutive deposition of naturally charged particles on lunar surface were troublesome in previous NASA explorations. Protecting sensitive surfaces from dust deposition in the limiting condition of the lunar atmosphere is imperative for future space exploration. This study reports experimental investigation of the collection efficiency of an electrostatic lunar dust collector (ELDC). A dual-functional remotely controlled particle charger/dropper was designed for tribocharging 20 μm lunar dust simulants, and a system of Faraday cup connected to an electrometer working in the nC range was used to measure the particle charges. Tribochargeability of two lunar dust simulants was studied, and the process was found to be the most effective with the JSC-1A samples. Aluminum was verified to be a more effective plate material than stainless steel. For the tested range of electrostatic field strength (0.66–2.6 kV/m), the mass-based and charge-based collection efficiencies were in the range of 0.25–1% and 0.45–1.45% for the low vacuum (10⁻¹ Torr), and 8–35% and 12–54% for the high vacuum (10⁻⁵ Torr) conditions. The linear relationship between the applied voltage and ELDC collection efficiency predicted by the theoretical model was confirmed, and the collection pattern of the collected particles over the collection plate was consistent with the previously computed charge distribution on the collection plate. Aside from validating the predictability of the theoretical model, this study offers a novel method of particle charging inside a vacuum chamber with a variety of applications for studying chargeability of particles at different temperatures and pressures.     

Electrostatic Evaluation of a Unipolar Diffusion and Field Charger of Aerosol Particles by a Corona Discharge

This article presents a unipolar diffusion and field charger by corona discharge is presented and electrostatically evaluated for charging aerosol particles. The electrostatic characteristics of the charger were investigated with an electrometer by measuring the ion number concentrations corresponding to the discharge and charging currents. The discharge and charging currents, and ion number concentration in the discharge and charging zones of the charger, increased with corona voltage. The magnitudes of the ion number concentration for positive and negative coronas in the discharge zone ranged from 1.34 × 10¹³ to 1.84 × 10¹⁵ ions/m³ and 7.34 × 10¹³ to 2.64 × 10¹⁵ ions/m³, respectively. For the charging zone, the ion number concentrations for positive and negative coronas ranged from 2.95 × 10¹³ to 1.52 × 10¹⁴ ions/m³ and 2.06 × 10¹³ to 1.47 × 10¹⁴ ions/m³, respectively. To predict the behavior of the electric field strength and lines in the discharge and charging zones of the charger, the electric field strength and distribution of the charger in the discharge and charging zones were calculated by a commercial computational fluid dynamics software package. Numerical calculation results of electric field distribution and lines through the inner electrode showed good agreement with experimental results. Also, the mean charge per particle for particle diameters were in the range of 0.01 to 50 µm for various operating conditions of the charger was theoretically evaluated. For both diffusion and field charging, lower aerosol flow rate and higher corona voltage resulted in an increase in the mean charge per particle within the charger. This simple charger proved to be particularly useful in diffusion and field charging of aerosol particles in particulate matter detector instruments for measuring PM10 and PM2.5 concentration.     

Preparation of monodisperse charged droplets via electrohydrodynamic device for the removal of fine dust particles smaller than 10 μm

Electrohydrodynamic (EHD) device is utilized in various applications and could be useful for the suppression of particulate matter in ambient conditions. In this study, we focused on the ejection of charged droplets containing electrolytes in a microdripping mode and with high charge density. Several different electrolytes with different physical and electrical properties were tested for our EHD process in order to produce the charged droplets stably. Results from series images by high-speed camera represented that droplet size and frequency were dependent on the applied voltage and flow rate, and showed different behaviors in various EHD modes such as dripping, microdripping, mixed dripping, and unstable dripping. Consecutive experimental data for charge density showed that 15?wt% KCl solution was proper to obtain highly charged droplets with the size from 50 to 100?μm. For this solution, the suppression of the fine dust particle was tested for the removal of PM10, PM2.5, and PM1 at various applied voltages. The droplet formation in microdripping mode was effective for the removal of smaller dust particles and could be applicable for the air remediation in indoor or domestic environment.     

烟道凝聚器流场及细颗粒凝聚特性研究

为研究烟道凝聚器的凝聚机制及颗粒物减排特性,通过商业计算流体力学（computational fluid dynamics,CFD）软件,模拟并得到了凝聚器湍流区定常/非定常工况条件下的流场特性;理论计算了凝聚器内颗粒的凝聚过程,并通过扫描电镜进行了验证;实验室中凝聚器对PM2.5的减排幅度为20.8%,实际工程中,300 MW和660 MW机组PM2.5的减排幅度分别为30.1%和37%。研究结果可为颗粒凝聚技术的大规模工程应用提供参考。     

Design and Evaluation of Four-Stage Low-Pressure Cascade Impactor Using Electrical Measurement System

The low-pressure cascade impactor has been used to collect ultrafine particles that cannot be measured by conventional cascade impactors. Low-pressure cascade impactors resemble ordinary impactors, but are operated at reduced pressures of 0.05 ～ 0.4 atm. Many kinds of low-pressure impactors have been developed by different researchers. However, it is still difficult to accurately design and evaluate the low-pressure cascade impactor.

In this study, a four-stage low-pressure cascade impactor for measuring the size distribution of submicron aerosol particles was designed and evaluated. To evaluate particle collection efficiency of each stage, an electrical measurement system was used. The cut-point diameters of Stages 1 through 4 were 0.238, 0.173, 0.111, and 0.063 μm in aerodynamic diameter. Stage 2 showed poor steepness of the collection efficiency curve and larger cut-point Stokes number than theory, which may be attributed to high nozzle velocity. The fluorometric method for particle collection efficiency measurement was shown to be unreliable for ultrafine particles.

The solid particle collection efficiency of the designed impactor was examined with different substrate conditioning methods. Porous metal substrate and silicon-coated substrate were tested with NaCl particles. It was shown that silicon coating did not effectively reduce the particle bounce because of high nozzle velocity, whereas the porous metal substrate considerably enhanced the particle collection efficiency.     

PRELIMINARY PERFORMANCE TESTS OF A PULSED JET PLEATED PAPER CARTRIDGE FILTER SYSTEM

ABSTRACT

A pulsed jet pleated paper cartridge filter system was tested for particle removal efficiency and operating stability using agricultural limestone as the test dust. The test system consisted of 6 pleated paper filter units arranged in parallel, each unit having an effective filtration area of 18.1 square meters. The system was operated at constant pressure drops of 6.25, 7.50 and 8.75 kPa (2.5, 3.0 and 3.5 inches of water), with face velocities of 0.78 to 1.04 m/ min (2.5 to 3.4 feet per minute) and dust loadings ranging from 0.5 g/ m to 2.5 g/ m³. Penetration through the media appeared to be relatively independent of dust loading, and efficiencies were in the 99.95 + % range. Slightly lower efficiencies were found for particles having diameters of 0.3 to 1.0 micrometers. A measure of the redeposition of dust pulsed from the filter was required to describe the effects on the pulse rate caused by changes in system flow and pulsing set point. Increased redeposition was found to occur with increasing flow rate, causing an increase in the pulse rate required to maintain operation of the system at a pulsing set point. Overall, the reverse pulse jet pleated paper cartridge filter system displayed extremely high particle removal efficiency in a compact unit that operated with low differential pressure.     

Filtration of dust in a circulating granular bed filter with conical louver plates (CGBF-CLPs)

A novel circulating granular bed filter with conical louver plates (CGBF-CLPs) was designed to remove dust particulates from the flue gas stream of a coal power plant. The purpose of this investigation was to evaluate the performance of the CGBF-CLPs. Dust collection efficiency and pressure drop data were analyzed to determine better operating conditions. The effect of solid mass flow rate, collector particle size and dust/collector particles separator types on the dust collection efficiency and pressure drop in the CGBF-CLPs were investigated in this study. The solid mass flow rate (B) varied from 15.59+/-0.44 to 20.36+/-0.68 g s(-1) and the initial average collector particle sizes were 1500 and 795 microm, respectively. Two types of separators, a cyclone and an inertial one, for separating the dust and collector particles were used in the CGBF-CLPs system. An Air Personal Sampler (SKC PCXR8) was used to determine the inlet and outlet dust concentrations. A differential pressure transmitter and data acquisition system were used to measure the pressure drop. Experimental results showed that the highest dust collection efficiency was 99.59% when the solid mass flow rate was 17.08+/-0.48 g s(-1) and the initial average collector particle size was 795 microm with the cyclone type separator. The results showed that the attrition fines of the original collector particles returning to the granular bed filter (GBF) reduced bed voidage. This phenomenon significantly increased the dust collection efficiency in the CGBF-CLPs. As a consequence, a bigger bed voidage creates a lower dust collection efficiency in the GBF.     

声凝并中颗粒间相互作用研究进展

声凝并是细颗粒物(PM2.5)排放控制的重要技术途径,其通过外加声场作用促进PM2.5发生碰撞凝并,使得颗粒数目减少、粒径增大,从而提高后续除尘装置的效率。对声凝并中颗粒间的相互作用机理,包括同向相互作用、声尾流效应、互辐射压力效应、互散射效应的相关研究进行总结和评述,结合声凝并技术在PM2.5排放控制中的应用,指出已有研究在理论模型和实验观测上存在的问题,进而提出今后的研究应在实验方法上进行创新,发展出能够跟踪微米和亚微米尺度PM2.5颗粒或颗粒团相互作用过程细节信息的实验手段,为理论模型的实验验证提供数据支撑;同时应进一步发展理论模型,从而在模型验证的基础上,充分发挥数值模拟的优势,全面识别声凝并中颗粒间相互作用的动力学行为。     

Research on wet-type swirl dust collection technology and its application in underground excavation tunnels

Wet-type dust collectors are widely used in underground excavation tunnels to control dust pollution. Nozzles and filter screens easily blocked by deposited scale and sticky dust, however, are usually a challenging problem for traditional wet-type dust collectors. This increases the cleaning workload and reduces the service life of the equipment. To address this issue, a wet-type swirl dust collection method without using spray nozzles and filter screens is proposed, and a novel wet-type swirl dust collector is designed. Experiments and field application of the wet-type swirl dust collector were carried out. Experimental results showed that the optimum water intake of the dust collector was 1.0 m³/h at 1480 r/min^?1 impeller speed; the dust suppression efficiency of the dust with particles size less than 75 μm was 93%, and that of dust with particles size of 180–250 μm was 95.2%. The field application in China's Tongqing Mine indicated that the respirable dust at the roadheader driver was reduced to 6.9 mg/m³, with a dust removal rate of 92.0%. The wet-type swirl dust collector effectively improves the dust collection efficiency and makes up for the problem of nozzles and filter screens being easily blocked in underground excavation tunnels by the traditional methods.     

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.     

Status of PM in Seoul metropolitan subway cabins and effectiveness of subway cabin air purifier (SCAP)

The increasing importance of indoor air quality management on public transport led the Korean government to amend the indoor air quality control in public use facilities, etc. Act including modes of public transport under the Act from June 2013. Particulate matter (PM) in subway systems is reported as being mostly generated by friction—between the wheels and the rails, between the wheels and the brake pads, and between the catenaries and the pantographs. In order to reduce PM level in subway cabins, a newly developed subway cabin air purifier (SCAP) was installed on the ceilings of the cabins. In this study, we analyzed indoor PM concentrations through continuous measurement of PMs less than 10 μm in diameter (PM₁₀) and PMs less than 2.5 μm in diameter (PM_2.5) in the cabins of line 2 and line 5 of the Seoul metropolitan subway network, comparing the concentrations in cabins where SCAP devices were installed to cabins without them in order to verify SCAP effectiveness. In both cabins with and without SCAP, the ratio of indoor to outdoor PM₁₀ (I/O for PM₁₀) showed a two-times higher value in line 5 than in line 2, which indicated that the entirely underground line 5 was less ventilated with outdoor air. In addition, the ratio of indoor PM_2.5/PM₁₀ showed that coarse mode PM was more abundant in line 5 due to poor ventilation in the tunnel sections compared to that of line 2. Regarding the effectiveness of SCAP, it was found that changes of PM₁₀ concentrations in line 2 and line 5 were from 132.8 to 112.2 μg/m³ (15.5 % efficiency) and from 154.4 to 114.2 μg/m³ (26.0 % efficiency) after SCAP installation, respectively.     

Synthesis of Sr4Al14O25:Eu2+ green emitting luminescent nano-pigment by solution combustion method

Luminescent nano-pigments based on strontium aluminates doped with various amounts of europium rare earth ion (Sr₄Al₁₄O₂₅:Eu²⁺) were synthesized by solution combustion method which involves the exothermic reaction of an oxidizer and an organic fuel. It is a suitable method for producing chemically homogenous and pure powders with very fine particle size. Phases studies by X-ray diffractometer indicated formation of pure phase Sr₄Al₁₄O₂₅ with crystallite sizes about 52.46 nm and peak shift of about 2θ = 0.26° due to Eu²⁺ doping. scanning electron microscope micrographs also revealed that the particles have irregular morphology and wide particle size distribution. The emission spectrum showed main emission peak at about 480 nm. Energy transfer mechanism between the two emission centers and the effect of Eu²⁺ ion concentration on emission spectrum was studied and it was deduced that the maximum emission intensity occurred at 4 at% of Eu²⁺. Absorption spectrum of the samples were lower than 0.5 %, especially in emission region of the doped pigments.     

Enhanced collection of fine particles in a cyclone using ultrasonic vapor with surfactants

Using water vapor to improve the efficiency of dust removal in gas cyclones was recently proposed. However, some dust particles are not hydrophilic which can reduce the effectiveness of the vapor. This paper investigates using surfactants to overcome such a difficulty. In particular, surfactants are added to the water solution which is atomized into vapor and added in a cyclone dust collector. The effects of surfactant type and quantity on the removal efficiency of the cyclone are studied by a series of experiments. Three surfactants are used to change the wettability of the two types of fine particles to be collected: molecular sieve dust and white carbon black. The particles in the cyclone are found to form agglomerates, which are measured by using a laser particle size analyzer and scanning electron microscopy. The results show that the addition of surfactants can greatly enhance the agglomeration and thus improve the collection efficiency, especially for particles approximately two microns in size. This indicates that using the atomized vapor with containing surfactants is an effective way to enhance the collection of fine particles in a cyclone separator.     

Polarized polymer films as electronic pulse detectors of cosmic dust particles

A dust particle detector based on a new physical principle of detection is described. The basic detecting element requires no bias voltage and consists of a thin film of the polarized polymer polyvinylidene fluoride (PVDF) having conducting electrodes on each of its surfaces. A high velocity (～10 km/s range) dust particle entering the detector removes dipoles along its trajectory. This produces a local depolarization, which results in a fast (ns range) charge pulse signal in the external circuit which is detected using pulse electronics. A theory has been developed for this new mechanism of pulse detection. The dependence of signal amplitude on particle mass and velocity has been measured for several PVDF detectors having thickness in the range 2–28 μm and area in the range 4–150 cm² using iron particles with velocity in the range ～1–12 km/s and mass in the range ～ 10^?13–10^?10 g. In addition, measurements carried out using a two-detector arrangement show that time of flight information may be obtained. Experimental results are presented which show, for example, that PVDF detectors have mass detection thresholds in the range ～10^?14–10^?12 g, at an impact velocity of 10 km/s, which compare favorably with mass thresholds reported for current dust detectors based on other physical principles. PVDF detectors have the advantages of being inexpensively and easily fabricated, tough, flexible and radiation resistant (to at least 10⁷ rad). They exhibit long term stability, and may be operated for extended periods of time over the temperature range ?50°C to + 50°C. In addition, their fast response permits a detector-pulse electronics system to count dust impacts at event rates up to 10⁴ s^?1 with no corrections required, and they have a response to dust particle impacts which is unaffected by high background fluxes of charged particles. As an example of the application of PVDF dust detectors, a detector is described which is being carried on space probes to measure the mass and flux of dust particles from Halley's Comet in March 1986. Other important applications for experiments in space are discussed.     

空气中PM2．5颗粒形成过程初探

文章主要研究了黑色金属冶炼及压延加工业PM2．5的排放特征,采用ELPI（Electrical Low Pressure Impactor）静电低压撞击器对烟气中的颗粒的粒数分布及质量浓度分布进行在线分析,通过自动烟尘测试仪采集样品,并对颗粒物的形貌、聚集特性、化学组分及物相组成等进行了深入研究,为中国工业排放PM2．5颗粒的来源分析及PM2．5对健康、气候的影响提供了有力的数据依据。     

The influence of third-body particles on wear rate in unicondylar knee arthroplasty: a wear simulator study with bone and cement debris

The reduced intraoperative visibility of minimally invasive implanted unicondylar knee arthroplasty makes it difficult to remove bone and cement debris, which have been reported on the surface of damaged and retrieved bearings. Therefore, the aim of this study was to analyze the influence of bone and cement particles on the wear rate of unicompartmental knee prostheses in vitro. Fixed bearing unicompartmental knee prostheses were tested using a knee-wear-simulator according to the ISO standard 14243-1:2002(E) for 5.0 million cycles. Afterwards bone debris (particle size 671 ± 262 μm) were added to the test fluid in a concentration of 5 g/l for 1.5 million cycles, followed by 1.5 million cycles blended with cement debris (particle size 644 ± 186 μm) in the same concentration. Wear rate, knee-kinematics and wear-pattern were analyzed. The wear rate reached 12.5 ± 1.0 mm³/million cycles in the running-in and decreased during the steady state phase to 4.4 ± 0.91 mm³/million cycles. Bone particles resulted in a wear rate of 3.0 ± 1.27 mm³/million cycles with no influence on the wear rate compared to the steady state phase. Cement particles, however, lead to a significantly higher wear rate (25.0 ± 16.93 mm³/million cycles) compared to the steady state phase. The careful removal of extruded cement debris during implantation may help in reducing wear rate. Bone debris are suggested to have less critical influence on the prostheses wear rate.     

ROOM-TYPE AIR CLEANER DESIGN CRITERIA AND PROTOTYPE PERFORMANCE

ABSTRACT

Two rules-of-thumb for minimum performance of a room-type air cleaner have been developed from consideration of a first order model for room air quality. By adopting a criterion that the use of an air cleaner should cause the particle concentration to be at least cut in half, the rule-of-thumb for a room with no smokers is that the product of filter efficiency and flow rate should be ≥.8 m³/min (≥30 cfm). If the particle concentration is dominated by smokers or other sources, the product of filter efficiency and filter flow rate should be = m³ /min (= 100 cfm)

Tests were conducted to determine the efficiencies of candidate filter media. The selected media, Filtrete G-0115, has a fractional efficiency for 1 μm particles of 97 percent when clean, and an efficiency of 78 percent when fully loaded. This drop in efficiency is due to the masking of the electrets on the surfaces of the filter fibers.

A fibrous filter room-type air cleaner was designed to perform in accordance with the rules-of-thumb. When operated with a clean filter, the maximum flow rate is 3.2 m³/min and, when operated with a fully loaded filter, the maximum flow rate is 1.8 m³/min. The system has a multispeed fan which will provide lower flow rates.