Unipolar and bipolar diffusion charging of ultrafine aerosol particles

Adachi, Motoaki; Kousaka, Yasuo; Okuyama, Kikuo

doi:10.1016/0021-8502(85)90079-5

Cited by 294 publications

(209 citation statements)

References 16 publications

Supporting

Mentioning

199

Contrasting

Unclassified

Order By: Relevance

“…Results obtained with the Boltzmann distribution could be quite different from those obtained with other reasonable charge distributions for other circumstances, for example, for nonequilibrium aerosols or for particles that are in equilibrium in an ionic atmosphere that is not purely bipolar, not having equal diffusivities among the ionic species (see, for example, Porstendorfer et al, 1984;Adachi et al, 1985). In the atmosphere, the negative ions tend to have higher mobility and diffusivity than the positive ions, leading to about a factor of two more negative than positive charge on particles much smaller than 1 pm (Adachi et al, 1985).…”

Section: Aerosol Charge Distributionmentioning

confidence: 97%

See 1 more Smart Citation

Predicted Deposition of Submicrometer Particles Due to Diffusion and Electrostatics in Viscous Axisymmetric Stagnation-Point Flow

Cooper¹,

Peters²,

Miller³

1989

Aerosol Science and Technology

View full text Add to dashboard Cite

Various mathematical solutions to the convective-diffusion equation for noninteracting Brownian particles were carried out to predict deposition of submicrometer particles onto a flat surface in viscous, three-dimensional (axisymmetric) stagnation-point flow at clean-room velocities ( -100 cm/s). The particle deposition aspects modeled included electrostatics, inasmuch as both difision and electrostatics are the dominant mechanisms expected. The results were obtained in terms of dimensionless groups for deposition, convective-diffusion, and electrostatic attraction. It was found that the deposition velocity can be well approximated by a simple combination of the convective-diffusion velocity and the eletrostatic velocity. These results are translated into practical terms, examples are given, and the predictions are compared with predictions made by other methods. A disk 20 cm in diameter charged to 2000-V potential is shown to attract a particle 0.1 pm in diameter so as to produce an electrostatic deposition velocity 180 times larger than the diffusion deposition velocity, giving it a deposition velocity nearly equal to that of a particle 10 pm in diameter settling under gravity.

show abstract

Section: Aerosol Charge Distributionmentioning

confidence: 97%

“…In the atmosphere, the negative ions tend to have higher mobility and diffusivity than the positive ions, leading to about a factor of two more negative than positive charge on particles much smaller than 1 pm (Adachi et al, 1985).…”

Section: Aerosol Charge Distributionmentioning

confidence: 99%

Predicted Deposition of Submicrometer Particles Due to Diffusion and Electrostatics in Viscous Axisymmetric Stagnation-Point Flow

Cooper¹,

Peters²,

Miller³

1989

Aerosol Science and Technology

View full text Add to dashboard Cite

show abstract

“…C c (Kn i ) is the empirical Cunningham (1910) correction factor, which is a function of Kn i , the momentum Knudsen number (Friedlander 2000) for entity i, as opposed to the diffusive Knudsen number, which applies to mass transfer processes and is dependent upon f i . Finally, in the nondimensionalization of Fuchs' diffusion charging theory, the mean free path of the diffusing entity is taken to be (1.329/f i )(kTm i ) 1/2 (Adachi et al 1985) and the expression given by Natanson (1960) is used to determine the limiting sphere radius. With these definitions, all six examined collision kernel expressions appropriately collapse into the form H(Kn D ), allowing for comparison to mean first passage time calculations.…”

Section: Comparison To Existing Kernelsmentioning

confidence: 99%

“…With recent advances in computational capabilities, Brownian dynamics simulations can accurately predict thermally driven particle-particle collision rates (the Z → ∞ limit); hence, they should be able to provide a means for more detailed examination of collision kernel expressions than is possible with currently available experimental approaches. Second, various authors have used different definitions for the mean persistence distance of the colliding entities (Jeans 1954;Dahneke 1983;Adachi et al 1985;Rader 1985;Sceats 1989;Gatti and Kortshagen 2008), and hence different definitions of the dimensionless parameter (i.e., the ratio of the persistence distance to the collision radius) used to determine whether a collision is continuum, free molecular, or transition regime process. We refer to this parameter as Kn D , the diffusive Knudsen number (Loyalka 1976;Dahneke 1983;Rogak and Flagan 1992), which must approach zero in the continuum limit and approach ∞ in the free molecular limit.…”

Section: Introductionmentioning

confidence: 99%

Determination of the Transition Regime Collision Kernel from Mean First Passage Times

Gopalakrishnan

Hogan

2011

Aerosol Science and Technology

View full text Add to dashboard Cite

Particle-vapor molecule (condensation) and particle-particle (coagulation) collision kernels are critically important parameters for the description of particle size distribution evolution in aerosols. We use mean first passage time calculations to find a dimensionless form of the collision kernel that applies in the limit where the ratio of the masses of colliding entities (aerosol particles or vapor molecules) to gas molecule mass, Z, approaches infinity, and the colliding entities are dilute in concentration. In these calculations, the motion of colliding entities is monitored with Langevin dynamics, and the collision kernel is inferred from the time required for collision. The presented analysis reveals that the dimensionless collisional kernel (H) is a function solely of the diffusive Knudsen number (Kn D , the square root of the product of kT and the reduced mass divided by the product of the reduced friction factor and collision radius), and a number of commonly used expressions for the collision kernel also collapse to the functional form H(Kn D ), irrespective of whether they were derived for Z → ∞ or Z → 0 conditions. The examined collision kernel expressions are further found to agree within 10% of our calculations as well as with each other across the entire Kn D range. This result suggests that a single collision kernel can be used to describe all transition regime collision rates, i.e., both condensation and coagulation rates, with reasonable accuracy, and establishes that Langevin-equationbased mean first passage time calculations can serve as a simple approach to examine transition regime collision phenomena.

show abstract

“…The concept is based on the charging of aerosol particles by the corona-produced unipolar air ions (Adachi et al, 1985;Hernandez-Sierra et al, 2003;Wiedensohler et al, 1994) in the vicinity of a respirator. The continuously emitted ions impose significant electric charges of the same polarity on the airborne particles and the mask surface.…”

Section: Introductionmentioning

confidence: 99%

Filtering Efficiency of N95- and R95-Type Facepiece Respirators, Dust-Mist Facepiece Respirators, and Surgical Masks Operating in Unipolarly Ionized Indoor Air Environments

Lee

Yermakov

Grinshpun

2005

Aerosol Air Qual. Res.

View full text Add to dashboard Cite

The emission of unipolar air ions in the vicinity of a filtering facepiece respirator has been recently shown to considerably enhance its respiratory protection efficiency. The effect is driven by the electric repelling forces that develop between the unipolarly charged mask and the aerosol particles, thus creating a shield for the incoming particles and consequently decreasing the penetration efficiency through the filter. The manikin-based preliminary evaluation of this concept has been performed with a very limited number of variables. In this study, four types of half-mask facepiece filtering devices (N95, R95, and dust-mist respirators, as well as surgical masks), operating at two different breathing flow rates, were tested with unipolar air ion emitters exhibiting different emission rates and polarities. The particle penetration efficiency through the facepiece filter was determined in a room-size indoor test chamber by a real-time particle size selective aerosol monitoring performed inside and outside of the mask, which was face-sealed onto a manikin. Three commercially available ionic air purifiers were utilized as air ion emitters. For the targeted particle size range of ~0.04 -1.3 µm, a 12-minute air ionization in the vicinity of a manikin enhanced the respiratory mask performance by a factor ranging from 1.61 to 3,250, depending on the respirator type, breathing flow rate, and the ion emission rate. The effect was achieved primarily within the first 3 minutes.

show abstract

Unipolar and bipolar diffusion charging of ultrafine aerosol particles

Cited by 294 publications

References 16 publications

Predicted Deposition of Submicrometer Particles Due to Diffusion and Electrostatics in Viscous Axisymmetric Stagnation-Point Flow

Predicted Deposition of Submicrometer Particles Due to Diffusion and Electrostatics in Viscous Axisymmetric Stagnation-Point Flow

Determination of the Transition Regime Collision Kernel from Mean First Passage Times

Filtering Efficiency of N95- and R95-Type Facepiece Respirators, Dust-Mist Facepiece Respirators, and Surgical Masks Operating in Unipolarly Ionized Indoor Air Environments

Contact Info

Product

Resources

About