In natural clouds, water droplets grow by condensation in a supersaturated environment. Under subsaturatedconditions, water droplets normally keep evaporating until they eventually disappear. In this article, we study the effect of corona discharge on water droplet growth under both supersaturated and subsaturated conditions. It is shown that the formation of mist visible to the naked eyes could be induced by direct current (dc) corona discharge under supersaturated conditions. Furthermore, we find that corona discharge could promote the growth of water droplets even under subsaturated conditions. Possible mechanisms are discussed, and the results suggest that the droplet growth enhancement is supported by the synergetic effects of droplet surface charge, external electric field, and ionic wind generated by the corona discharge. (direct current corona discharge)
- Coalescence ,
- condensation ,
- corona discharge ,
- water droplet growth
- Discharges (electric),
- Semiconductor device measurement,
- Temperature measurement
GROWTH of nanometric and micrometric particles or droplets suspended in the gas phase is important in a number of natural and industrial processes, such as microelectronics manufacturing, nanomaterial synthesis, and environmental remediation. Specifically, water droplets in the atmosphere, both in liquid and solid-state, have significant effects on cloud formation, precipitation, and climate change . Traditional static cloud seeding relies on spray-ing substances such as silver iodide and dry ice, whose crystal structure is similar to ice, to convert supercooled water droplets into ice and accelerate their growth through the Bergeron–Findeisen process. For warm cloud seeding, hygroscopic salts are frequently used to serve as artificial cloud condensation nuclei (CCN) . The aim of both seeding technologies is to promote the growth of water droplets or particles in the cloud to attain the size needed for triggering the natural process of collisions. It has long been demonstrated that the presence of electrical charges on a droplet causes the equilibrium vapor pressure o decrease, leading to a favorable condition for condensation . Water droplets can become electrically charged through different processes. For example, charged droplets occur in the natural environment by radiation of galactic cosmic rays (GCRs), which modulate the conduction current flowing between the ground and ionosphere. A close correlation was observed between the GCR intensity and cloud coverage over the earth, attracting special interest in the role of the charge effects playing in the microphysics process inside the cloud . Recently, different methods, including femtosecond laser pulses –, ultraviolet (UV)light , and corona discharge , , have been observed to be able to induce water condensation in the air. The effect of femtosecond laser on producing aerosols in nano and micrometer range, as well as generating snow and rain, has been investigated extensively. In addition to ion-induced nucleation (IIN), Heninet al. and Kasparianet al.attributed the mechanism of laser-induced condensation to the production of hygroscopic trace gases in laser filaments.Yo s h i h a r aet al. showed rapid water droplet production within a soap bubble by 185-nm UV radiation. They proposed that UV-generated hygroscopic hydrogen peroxide may act as the nucleation precursor . For corona discharge, multiple groups demonstrated the feasibility of utilizing high-voltage discharge to induce the formation of rain and snow in super-saturated conditions , . More recently, the effect of corona discharge on the rate of water vapor nucleation and condensation in steam was investigated. The condensation rate was improved by 16% using a benchtop steam condenser system , .
Previous studies regarding corona-induced condensation were mostly focused on the macroscopic phenomenon of the effect. In this article, we study the effect more closely under both supersaturated and subsaturated conditions. It was shown that the formation of mist visible to the naked eyes could be induced by direct current (dc) corona discharge under supersaturated conditions. It was further demonstrated that even under subsaturated conditions, the presence of corona discharge could promote the growth of smaller water droplets. Possible mechanisms that could contribute to the process were discussed.
In conclusion, we report the enhancement of water droplet growth by corona discharge in both supersaturated and subsaturated conditions. Different effects that may contribute to the droplet growth are discussed. The synergetic effect of droplet surface charge, external electric field, and ionic wind may be the reason for the observed phenomenon. A systematic study is needed to investigate the influence of different parameters, including temperature, humidity, and applied voltage, on the droplet growth process.
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FULL Paper PDF file:Corona Discharge-Induced WaterDroplet Growth in Air
Corona Discharge-Induced WaterDroplet Growth in Air
in IEEE Transactions on Plasma Science, vol. 48, no. 7, pp. 2437-2441, July 2020,
PDF reference and original file: Click here
Professor Siavosh Kaviani was born in 1961 in Tehran. He had a professorship. He holds a Ph.D. in Software Engineering from the QL University of Software Development Methodology and an honorary Ph.D. from the University of Chelsea.