共查询到20条相似文献,搜索用时 46 毫秒
1.
A novel aerosol charger has been developed, which has high efficiency and high throughput especially for nanometer particles in the size range of 3–50nm. Unipolar charging with high ion concentration and long charging time is used to obtain the high charging efficiency. High throughput is achieved by reducing particle loss within the charger. This is accomplished by directing ion flow and aerosol flow in the same direction and by the use of sheath air flow. The charger configuration is of a longitudinal design – the direction of aerosol stream and ion stream are flowing parallel along the longitudinal axis of the charger. The charger consists of four sections: the inlet zone, the ion production zone, the unipolar charging zone, and the exit zone. In the inlet and ion production zones, unipolar ions are generated using Po210 radioactive sources with an electric field designed to separate the positive and negative ions, and to focus the selected unipolar ions into the core region of the charger. The ions with the selected polarity is then attracted to the charging zone by an uniform electric field created by a series of ring electrodes applied with a linear ramped voltage. Aerosol entering the charger is sheathed with clean gas flow in order to keep the aerosol in the core region. A novel exit design with a reversed electric field is incorporated in order to minimize the charged particles loss. The performance of the charger is first evaluated using computer simulation and then constructed for experimental validation. Experiment data have demonstrated that the charger achieves 90% and 95% charged-particles penetration efficiency and with 22% and 48% extrinsic charging efficiency at 3 and 5nm particle sizes, respectively. These performance data represent significant improvement, over a factor of 10, compared with the existing chargers. 相似文献
2.
Dae Seong Kim Yong Min Kim Yong Taek Kwon Kihong Park 《Journal of nanoparticle research》2011,13(2):579-585
Three types of unipolar chargers (parallel multi-electrodes, single electrode, and single electrode with compact size) using
the soft X-ray were constructed and their charging performance was evaluated by measuring positive, negative, and neutral
fractions of size-resolved ultrafine particles (20–100 nm) with the Tandem Differential Mobility Analyzer (TDMA) technique.
The unipolar charger with a single electrode and compact size showed the highest charge fraction with least particle loss
probably due to lower electrostatic loss of ions among tested chargers. With positive voltage applied to electrode to remove
negative ions, we found that the positively charged particles were 43, 52, 62, 69, and 75% for 20, 30, 50, 70, and 100-nm
particles, respectively, and a few particles were negatively charged although their fraction increased with size (1, 2, 4,
5, and 6% for 20, 30, 50, 70, and 100-nm particles, respectively). The positive charge fractions were about three times higher
than the values estimated theoretically from a bipolar charger. Also, based on comparison of current data with previously
reported values using corona discharge unipolar charger, the soft X-ray charger showed better performance in terms of charging
efficiency and penetration for particles (NaCl) currently tested in the particle size range of 20–100 nm. 相似文献
3.
Panich Intra 《Journal of Electrostatics》2012,70(1):136-143
A cylindrical triode charger for unipolar diffusion charging of aerosol particles was designed, constructed, and evaluated. The corona discharge characteristics were studied in this cylindrical triode charger. For the process the current–voltage characteristics were determined, as were the ion number concentration, the nit product, and the mean charge per particle as a function of particle diameter. The discharge and charging currents, and ion number concentration in the charging zone of the charger increased monotonically with corona voltage. The negative corona had a higher current than the positive corona. At the same corona voltage, the ion number concentration in the discharge zone was larger than the charging current for positive and negative coronas, with values of about 197 and 32 times and 645 and 99 times for the ion-driving voltages of 0 and 310 V, respectively. The average ion penetration for positive and negative coronas was 0.64 and 0.19% and 3.62 and 1.93% for the ion-driving voltages of 0 V and 310 V, respectively. The higher flow rate, shorter residence time, gave a lower Nit product. By calculation 14% of charged particles of 10 nm in diameter were lost to the outer cylinder because of the electrostatic field effect. The charger does not use a sheath of air flow along the walls or the perforated screen opening, it has low diffusion and space charge losses due to the short column charging zone, and is a low complexity and inexpensive system. It worked as well as more sophisticated and expensive commercially available chargers. 相似文献
4.
Particle motion induced by electrical forces is the basis for important class of measuring instruments. Charging is important in aerosol size measurement. Unipolar charger is a crucial component in the aerosol particle sizing system by electrical mobility analysis. For an electrical mobility analyzer, the charging is aimed to impose a known net charge distribution on each aerosol size. The charger performance depends on the charging efficiency and stable operation. A well-designed unipolar charger should provide high charging efficiency and stability that can be accurately determined for any given operating conditions. This article presents and discusses progress on the development of existing unipolar aerosol chargers based on corona discharge technique. The operating principles as well as detailed physical characteristics of these chargers, including the corona-wire and corona-needle chargers, are described with extensive list of references. 相似文献
5.
《Journal of Electrostatics》2006,64(3-4):203-214
A methodology is proposed for the measurement of a number of parameters relevant to the performance evaluation of aerosol corona chargers. These parameters are intrinsic and extrinsic charging efficiencies, and diffusion and electrostatic particle losses. The methodology is essentially the same as that used in earlier works, except that free ions are removed just after the charger outlet in order to minimize the extent of possible after-charging effects which might lead to measurement errors. However, the experimental results show that after-charging is negligible and that, consequently, practically all the effective ion–particle collisions take place before the aerosol leaves the charger. Formation of new particles during corona discharge, which could in principle be an additional cause of measurement error, has not been observed in the working voltage range of the charger. Particle diffusion and electrostatic losses have been measured at varying values of the voltage applied to the charger: for a given particle size, diffusion loss decreases and electrostatic loss increases as the charger voltage is increased. The intrinsic charging efficiency increases with particle size and charger voltage. In contrast, the extrinsic charging efficiency, which is the parameter of importance in practice, attains a maximum value for a given charger voltage in such a manner that this optimum voltage depends on particle size. 相似文献
6.
Sonic jet chargers have originally been used in aerosol measurement devices for particle charging and neutralization. Here, our goal was to study if this charger type could be used in particle control devices in which particle concentrations and gas volumes are much higher. The study includes charging efficiency tests in a laboratory and with a commercial 20 kW wood pellet burner. Actual particle removal efficiency was tested with a laboratory scale parallel plate electrostatic collector. The results show that sonic jet-type chargers also have potential in filtering applications. 相似文献
7.
A new unipolar charger for aerosol nanoparticles has been developed. In this twin Hewitt charger two corona discharge zones are connected by a charging zone where the nanoparticle aerosol flows. Ions move into the charging zone alternating from each corona discharging zone by means of a square-wave voltage. The operation parameters of the device have been experimentally investigated at standard conditions with the goal to optimize the extrinsic charging efficiency in N2 carrier gas. It has been found that there exists an optimal length of the charging channel for each gas flow rate through the charger which minimizes losses of charged particles and at the same time having a sufficient large n
iont-product. Extrinsic charging efficiencies of some 30% for particles with a diameter of 10 nm are obtained. 相似文献
8.
In this paper, the corona discharge characterization in terms of current–voltage relationships of a unipolar cylindrical tri-axial charger on the effects of the corona wire diameter and length have been experimentally studied and discussed. A commercial computational fluid dynamics software package, COMSOL Multiphysics™, was used to predict the electric field distribution in the ion generation and charging zones of the charger and the ion penetration through the perforated screen opening on the inner electrode of the charger. It was found from experimental results that both positive and negative charging currents in the charging zone of the charger increased with increasing corona and ion-driving voltages. At the same corona and ion-driving voltages, both positive and negative coronas were decreased with increasing diameter of the corona-wire. Compared with the corona-wire of 22 mm in length, the magnitude of both positive and negative charging currents were markedly higher for corona-wire of 11 mm in length at the same corona voltage. It was found that the charging currents for negative coronas were about 1.2 times higher than those positive coronas at the same corona and ion-driving voltages. Numerical results of the electric field distribution and the ion and charged particles migrations in the discharge and charging zones of the charger is correlated to have the same direction with the experimental results of the current–voltage relationships. Also, this can be used to guidance in describing the electric field distribution and the behavior of ion and charged particle trajectories that cannot be seen from experiments in order to improve the applicably design and refinement of a unipolar cylindrical tri-axial charger. 相似文献
9.
A. V. Filippov V. N. Babichev V. E. Fortov A. V. Gavrikov A. F. Pal’ O. F. Petrov A. N. Starostin N. E. Sarkarov 《Journal of Experimental and Theoretical Physics》2011,112(5):884-895
The photoemission charging of dust particles under ultraviolet radiation from a xenon lamp has been investigated. The velocities
of yttrium dust particles with a work function of 3.3 eV and their charges have been determined experimentally; the latter
are about 400–500 and about 100 elementary charges per micron of radius for the positively and negatively charged fractions,
respectively. The dust particle charging and the dust cloud evolution in a photoemission cell after exposure to an ultraviolet
radiation source under the applied voltage have been simulated numerically. The photoemission charging of dust particles has
been calculated on the basis of nonlocal and local charging models. Only unipolar particle charging is shown to take place
in a system of polydisperse dust particles with the same photoemission efficiency. It has been established that bipolar charging
is possible in the case of monodisperse particles with different quantum efficiencies. Polydispersity in this case facilitates
the appearance of oppositely charged particles in a photoemission plasma. 相似文献
10.
M. Lackowski A. Krupa A. Jaworek 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2010,56(3):377-382
Charging of aerosol droplets and solid particles is applied in many
industrial processes such as electrostatic painting, particle separation and
electrostatic precipitation. In most of charging devices, electrical
discharges are used as a source of ions, which are deposited onto the
particles. In the present paper, the charging process by ionic current in
alternating electric field was optimized experimentally. Alternating
electric field charger was used as a charging device in these experiments.
The current voltage characteristics of electrical discharge in this device,
and the charge imparted to the particles were determined. The level of
charge was measured at the outlet of the charger and was compared to the
Pauthenier limit for different supply voltages, and frequencies. MgO powder
was used as a source of particles in these experiments. It was noticed that
higher supply voltage of the charger gives higher level of particle charge,
but at the same time, the particle deposition on the charger elements was
increased, decreasing the particle penetration. A compromise between these
two tendencies is therefore necessary. As a result we have proposed a
criterion maximizing the total charge born by the particles which is a
product of relative particle charge and particle penetration. 相似文献
11.
Charge distribution characteristics were investigated for nanoparticles synthesized in a diffusion flame aerosol reactor.
The nanoparticles considered were pristine TiO2 and Cu–TiO2, with Cu dopant concentrations ranging from 1 to 5 wt% with particle size from 25 to 60 nm. In situ measurements were conducted
by integrating a tandem differential mobility analyzer (TDMA) experimental setup with the flame aerosol reactor. A charging
model was used to identify the important parameters that govern the two charging mechanisms (diffusion and thermo-ionization)
in the flame and their relative importance at different operating parameters. The results indicate that TiO2 and Cu–TiO2 nanoparticles carry single as well as double unit charges. The charged fraction depends on particle size as well as on dopant
concentration. The charged fraction increased with increasing particle size and decreased with copper dopant concentration.
Measured charged fractions were similar for both the polarities at different mobility diameters. Based on the flame operating
parameters, the calculations indicate that diffusion charging is dominant in the flame, which is consistent with the experimental
results. 相似文献
12.
B. F. Gordiets E. Bertran 《Russian Journal of Physical Chemistry B, Focus on Physics》2008,2(2):315-328
A theoretical global model is presented for describing the kinetics of generation and growth of clusters and nanoparticles
in low-pressure plasmas, where important processes for clusters and grains are collisions with monomers, electrons, and ions
and particle coagulation and loss because of diffusion and gas flow drag. Simple equations are given for calculations of monomer
density, particle-size distribution function, critical cluster size, the rate of particle production and particle density
and mean size, and plasma characteristics (the densities and average energies of “cold” and “hot” electrons and the density
of positively charged ions). The model is self-consistent; that is, the above-mentioned properties of clusters, nanoparticles,
electrons, and ions are calculated jointly from coupled equations as functions of a small number of radio frequency (RF) discharge
parameters (discharge geometry; absorbed electric power; voltage across the RF sheath; gas pressure; composition; and flow
rate). Comparisons are made with the experimental data on SiH4-Ar mixtures.
Published in Russian in Khimicheskaya Fizika, 2008, Vol. 27, No. 4, pp. 79–93.
The article was translated by the authors. 相似文献
13.
A numerical analysis on the electrostatic capture of airborne viruses and nanoparticles in a homemade particle concentrator without a unipolar charger using commercial CFD software (CFD-ACE+) was presented. We simulated the effects of inlet/outlet configurations and particle diameters on the collection efficiency of the particle concentrator, and the simulation was in good agreement with the experimental measurements. We investigated the effects of the electrode arrangement on the collection efficiency. We also discussed the maximum collection efficiency and the relationship between the electric field intensity, the positions of the simulated particles on the inlet surface, and the collection efficiency. 相似文献
14.
Philipp Reissaus Tomas Waldemarsson Jürgen Blum Dominik Clément Isabel Llamas Harald Mutschke Frank Giovane 《Journal of nanoparticle research》2006,8(5):693-703
In order to find reliable collector surfaces for the Mesospheric Aerosol – Genesis, Interaction and Composition (MAGIC) sounding rocket experiment, intended to collect atmospheric nanoparticles, the sticking efficiency of nanoparticles was measured on several targets of different materials. The nanoparticles were generated by a molecular beam apparatus in Jena, Germany, by laser ablation (Al2O3 particles, diameter 5–50 nm) and by laser pyrolysis (carbon particles, diameter 10–20 nm). In a vacuum environment (>10−5 mbar) the particles condensed from the gas phase, formed a particle beam, and were accelerated to ∼
∼1 km/s. The sticking efficiency on the target materials carbon, gold and grease was measured by a microbalance. Results demonstrate moderate to high sticking probabilities. Thus, the capture and retrieval of atmospheric nanoparticles was found to be quantitatively feasible. 相似文献
15.
《Journal of Electrostatics》2007,65(4):209-220
A nanoparticle charging model considering simultaneous diffusion, direct photoionization and thermionization charging was developed. The model included a balance expression for the positive and negative ions, and one for each charge level of the particles. Three comparable parameters: attachment coefficient, β±(v,q), photoelectric yield coefficient, α+(v,q), and thermionic yield coefficient, γ+(v,q), were identified that govern different charging mechanisms. By comparing these parameters, the importance of different mechanisms was explored. Analytical (closed-form) solutions under certain unipolar and bipolar conditions were proposed. Literature reported experimental data on a soft-X-ray based unipolar charger was used to verify this model and fair agreement was achieved. A numerical algorithm was developed to solve the governing equations for a soft-X-ray enhanced electrostatic precipitator (ESP) system. The role of soft-X-ray irradiation at improving nanoparticle average charge and enhancing the ESP capture efficiency was demonstrated. Experimental tests with this system were also conducted. Measured capture efficiency showed excellent agreement with theoretical results. 相似文献
16.
A numerical investigation has been carried out to examine the electrostatic loss of nanoparticles in a corona needle charger.
Two-dimensional flow field, electric field, particle charge, and particle trajectory were simulated to obtain the electrostatic
deposition loss at different conditions. Simulation of particle trajectories shows that the number of charges per particle
during the charging process depends on the particle diameter, radial position from the symmetry axis, applied voltage, Reynolds
number, and axial distance along the charger. The numerical results of nanoparticle electrostatic loss agreed fairly well
with available experimental data. The results reveal that the electrostatic loss of nanoparticles increases with increasing
applied voltage and electrical mobility of particles; and with decreasing particle diameter and Reynolds number. A regression
equation closely fitted the obtained numerical results for different conditions. The equation is useful for directly calculating
the electrostatic loss of nanoparticles in the corona needle charger during particle-charging process. 相似文献
17.
The performance of an electrical aerosol detector (EAD; TSI Model 3070A) was experimentally evaluated for measuring the integral parameters of particles (i.e., total length concentration of particles, and the total surface area concentrations of particles deposited in a human lung). The EAD consists of a unipolar diffusion charger with an ion trap, and aerosol electrometer. We first evaluated the performance of the EAD charger. Both polydisperse and monodisperse particles of Ag, NaCl, and oleic acid (with the dielectric constants of infinite, 6.1 and 2.5) were then generated to evaluate the particle material effect on the EAD readout. 相似文献
18.
N. S. Tabrizi M. Ullmann V. A. Vons U. Lafont A. Schmidt-Ott 《Journal of nanoparticle research》2009,11(2):315-332
The production of nanoparticles by microsecond spark discharge evaporation in inert gas is studied systematically applying
transmission electron microscopy, mobility analysis and BET surface area measurement. The method of spark discharge is of
special interest, because it is continuous, clean, extremely flexible with respect to material, and scale-up is possible.
The particle size distributions are narrow and the mean primary particle size can be controlled via the energy per spark.
Separated, unagglomerated particles, 3–12 nm in size, or agglomerates can be obtained depending on the flow rate. The nanoparticulate
mass produced is typically 5 g/kWh. A formula is given, which estimates the mass production rate via thermal conductivity,
evaporation enthalpy and the boiling point of the material used. We showed that with gas purified at the spot, the method
produced gold particles that were so clean that sintering of agglomerated particles occurred at room temperature. The influence
of a number of parameters on the primary particle size and mass production rate was studied and qualitatively understood with
a model of Lehtinen and Zachariah (J Aerosol Sci 33:357–368, 2002). Surprisingly high charging probabilities for one polarity
were obtained. Spark generation is therefore of special interest for producing monodisperse aerosols or particles of uniform
size via electrical mobility analysis. Qualitative observations in the present study include the phenomenon of material exchange
between the electrodes by the spark, which opens the possibility of producing arbitrary mixtures of materials on a nanoscale.
If spark generation of nanoparticles is performed in a standing or almost standing gas, an aerogel of a web-like structure
forms between surfaces of different electrical potential. 相似文献
19.
Nanopowders are produced in a low temperature, non-equilibrium plasma jet (APPJ), which produces a glow discharge at atmospheric pressure, for the first time. Amorphous carbon and iron nanoparticles have been synthesized from Acetylene and Ferrocene/H2, respectively. High generation rates are achieved from the glow discharge at near-ambient temperature (40–80°C), and rise with increasing plasma power and precursor concentration. Fairly narrow particle size distributions are measured with a differential mobility analyzer (DMA) and an aerosol electrometer (AEM), and are centered around 30–35 nm for carbon and 20–25 nm for iron. Particle characteristics analyzed by TEM and EDX reveal amorphous carbon and iron nanoparticles. The Fe particles are highly oxidized on exposure to air. Comparison of the mobility and micrograph diameters reveal that the particles are hardly agglomerated or unagglomerated. This is ascribed to the unipolar charge on particles in the plasma. The generated particle distributions are examined as a function of process parameters. 相似文献
20.
Daniel A. Japuntich Luke M. Franklin David Y. Pui Thomas H. Kuehn Seong Chan Kim Andrew S. Viner 《Journal of nanoparticle research》2007,9(1):93-107
Two different air filter test methodologies are discussed and compared for challenges in the nano-sized particle range of
10–400 nm. Included in the discussion are test procedure development, factors affecting variability and comparisons between
results from the tests. One test system which gives a discrete penetration for a given particle size is the TSI 8160 Automated
Filter tester (updated and commercially available now as the TSI 3160) manufactured by the TSI, Inc., Shoreview, MN. Another
filter test system was developed utilizing a Scanning Mobility Particle Sizer (SMPS) to sample the particle size distributions
downstream and upstream of an air filter to obtain a continuous percent filter penetration versus particle size curve. Filtration
test results are shown for fiberglass filter paper of intermediate filtration efficiency. Test variables affecting the results
of the TSI 8160 for NaCl and dioctyl phthalate (DOP) particles are discussed, including condensation particle counter stability
and the sizing of the selected particle challenges. Filter testing using a TSI 3936 SMPS sampling upstream and downstream
of a filter is also shown with a discussion of test variables and the need for proper SMPS volume purging and filter penetration
correction procedure. For both tests, the penetration versus particle size curves for the filter media studied follow the
theoretical Brownian capture model of decreasing penetration with decreasing particle diameter down to 10 nm with no deviation.
From these findings, the authors can say with reasonable confidence that there is no evidence of particle thermal rebound
in the size range. 相似文献