Cloud droplet collision efficiency in electric fields

Plumlee, Hubert R.; Semonin, Richard G.

doi:10.3402/tellusa.v17i3.9067

Cited by 17 publications

(11 citation statements)

References 3 publications

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“…Certainly E• and/or E•. are affected by charging, as has been shown by Plumlee and Semonin [1965] and Neiburger et al [1974], respectively. The tendency seems to be an enhancement of E• and E•., though our treatment Levin 1974, 1975b] adequately shows that either enhancement or depletion effects can be expected.…”

Section: Errorsmentioning

confidence: 82%

Polarization charging may produce a large electric field before the radar echo maximum

Levin¹,

Scott²

1975

J. Geophys. Res.

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Numerous papers by Moore, Colgate, and Vonnegut have questioned the effectiveness of polarization charging in the generation of breakdown electric fields in thunderclouds, specifically directing their criticisms toward the recent numerical models of Ziv and Levin and Scott and Levin. This reply seeks to answer the points they raised and pinpoint the deficiencies in the models. Model results closely follow the available experimental data. The most significant model results are the following: (1) Larger electric fields are produced with a decrease in the effectiveness of the polarization charging mechanism. (2) Lightning can be produced before significant radar echos appear; the maximum radar returns then follow the lightning. These results stem from the extremely nonlinear interactions between precipitation formation and polarization charging. The mechanism is sufficiently effective that despite the hindering influences mentioned by Moore, Colgate, and Vonnegut, large electric fields are produced. INTRODUCTIONOf late a number of critical papers [Vonnegut, 1975; Moore, 1975a, b, c; Colgate, 1975] have appeared in the literature relating to polarization charging, the theoretical model of Levin and Ziv, [1974], and the more elaborate stochastic model of Scott and Levin [1974, 1975b] and Levin et al. [1974]. The authors of these papers view thunderstorm electrification from another viewpoint, i.e., the convective mechanism as classically presented in the s•andard references [e.g., Mason, 1971]. This reply attempts to answer all the points brought up, with Specific emphasis on the two preceding papers.At the outset we would like to emphasize that the models as presented are well-defined both mathematically and physically and that, provided one accepts their inherently limited validity, they can be used to estimate the microphysical effects of electrical charging. It is important that we recognize that the models contain no vertical dimension and no cloud dynamics. These are rather severe restraints, but the problem is a particularly intractable one.The first paper [Vonnegut, 1975] was answered by Levin and Ziv [1975]. In essence, Vonnegut questioned the assumption that the raindrops continually collide with a fresh stream of uncharged waterdrops. This deficiency has since been removed and does not apply to the stochastic model of Scott and Levin [1974, 1975b]. Hence no more reference need be made to this matter except to note that the deficiency did not affect the general nature of the numerical results.Since then Moore [1975a, b] has written two papers that essentially state the following: (1) Recombination of charged particles was omitted in the models. (2) Partial coalescence events only occur during collisions near the equator of the larger drop. Such collisions cannot generate charge. These papers have now been followed by the two preceding papers by Colgate and Moore.In replying to this criticism, particularly that in the two preceding papers, we shall deal with three major topics: the recombination problem, the ...

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Section: Errorsmentioning

confidence: 82%

Polarization charging may produce a large electric field before the radar echo maximum

Levin¹,

Scott²

1975

J. Geophys. Res.

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“…(3.3 KV/cm). Plumlee & Semonin (1965) found that the collision efficiency of a 50 /mi radius drop with a 10 pm droplet increases by a factor of about 1.3 when the horizontal field is changed from 0 to 3 600 V/cm, while in the same range of field strength the collision efficiency increases by a factor of 34.5 for the 30 and 5 pm droplet pair.…”

Section: Collision Efficiencymentioning

confidence: 95%

“…Computations of electric field influence on droplet collision efficiency have been made by several workers, especially by Krasnogorskaja (1965), Plumlee & Semonin (1965), and Sartor (1967). Krasnogorskaja (1965) predicts that two uncharged droplets of radius 15 pm and 25 pm having a collision efficiency of about 0.8 in the absence of a field, will attain values of 1.6, 5.2 and 8.4 in a vertical electric field strength of 2, 6, 10 KV/cm respectively.…”

Section: Collision Efficiencymentioning

confidence: 99%

Direct measurements of small water coalescence droplets in efficiency and frequency an electric field

Phan‐Cong

Dinh-Van

1973

Tellus A: Dynamic Meteorology and Oceanography

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Small water droplets with diameter d < 8 pm are allowed to fall in a settling chamber in the presence of a quasi-uniform electric field varying from zero t o 600 V/cm. The trajectories of these droplets are photographically recorded through an incident-light microscope with dark field illumination. Results from 2 000 photographs, each one containing about 25 droplet pairs, show that the coalescence efficiency is almost unity. The coalescence frequency is almost zero in the absence of an electric field and increases rapidly at fields stronger than 400 V/cm. The coalescence frequency increases about linearly with electric fields from 100 to 400 V/cm. A survey of coalescences of droplets with parallel trajectories gives some order of magnitude for the collision efficiency, which indicates that the influence of the electric field is very pronounced for small droplets.

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“…where ρ a (kg/m 3 ) and ρ p (kg/m 3 ) are the air and snow particles density, respectively; D (m) is the diameter of the cables; d p (m) is the diameter of the snow particles; and μ (pa•s) is the dynamic viscosity of the medium environment, which is air in this study. Several investigations have been done on collision efficiency of different types of atmospheric icing on objects with different geometries such as cylinder [23][24][25][26], stranded power transmission lines [27], and airfoils [28,29]. Wakahama had studied trajectories of snow particles by photographing them when they were impinging to or rebouncing from a cylindrical surface [30].…”

Section: Eoretical Sectionmentioning

confidence: 99%

Experimental and Theoretical Studies of Wet Snow Accumulation on Inclined Cylindrical Surfaces

Mohammadian

Sarayloo

Abdelaal

et al. 2020

Modelling and Simulation in Engineering

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Wet snow accumulation on bridge cables and its shedding due to external phenomena such as rise in temperature, wind, and gravity is a serious threat to the safety of cars and pedestrians crossing the bridge. Commonly the accumulated snow on bridge cables is removed by external means such as mechanical removal or heat treatment which are expensive, time-consuming, and high-risk processes and are conducted based on little or no information available regarding the actual size and shape of the accumulated snow. In addition, cleaning of cables using the mechanical methods can potentially lead to erosion of cable materials when applied over years, resulting in enhanced surface roughness and potentially increased wet snow/ice accumulation during future precipitation events, and sometimes might require replacement of cable stays, which is an extremely costly and complicated task. Optimizing the number of mechanical cleaning procedures such as chain release through predicting the shape and thickness of the accumulated snow on the cable stays reduces the cost, time, and risk associated with the process. In this study, wet snow accumulation on torsionally rigid inclined cylinders of high-density polyethylene (HDPE) has been studied experimentally and numerically. A 2-D numerical model has been developed utilizing weather data to predict the thickness and the shape of the accumulated wet snow on inclined cylindrical surfaces. Outdoor experiments were also conducted to measure the density and thickness of accumulated snow, while monitoring the weather data real time. Overall, snow density was found to be linearly increasing with an increase in wind velocity, during snow precipitation. The maximum thickness and shape of the accumulated snow on cables obtained from the numerical model were found to be in good agreement with the outdoor experimental data. This work aims to provide a mean for prediction of snow accumulation on surfaces for optimizing the efficiency of the costly and high-risk snow removal procedures.

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Cloud droplet collision efficiency in electric fields

Cited by 17 publications

References 3 publications

Polarization charging may produce a large electric field before the radar echo maximum

Polarization charging may produce a large electric field before the radar echo maximum

Direct measurements of small water coalescence droplets in efficiency and frequency an electric field

Experimental and Theoretical Studies of Wet Snow Accumulation on Inclined Cylindrical Surfaces

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