Abstract
As one of the emerging application areas of the corona discharge technique, rain enhancement induced by atmospheric air ionization has made a great breakthrough. Although natural rainfall modified by artificial ionization was successfully observed via the statistical data of field experiments, deficient efforts have been devoted to the research on the near-field effect of corona discharge on the evolution of water droplets around the discharge device. In this article, we studied the electrostatic effects of corona discharge on the spectrum and density evolution of water droplets in a 96-m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> cloud chamber. An interesting phenomenon was found that two different electrostatic effects appeared when various high voltages were applied on the corona electrode. In detail, the growth of droplets larger than 10 μm was detected once the applied high voltage exceeds the critical value (e.g. -80 kV in our discharge device), and this is attributed to the electrostatic induction effect. By contrast, a narrow droplet size spectrum and reduced density caused by the strong electrostatic precipitation effect were shown below this critical voltage. To figure out the mechanisms underlying these phenomena, the charging status of water droplets with various sizes, forces of charged droplets under various electric field strength, and collision kernels between droplets, are analyzed through theoretical calculations. Results show that the electric field plays a dominant role in the charging process of droplets and the acceleration of collision-coalescence between charged and neutral droplets, which results in the different electrostatic effects on the evolution of droplets. This article may provide some enlightenment to fog elimination in industrial application and cloud-seeding in atmospheric water resources comprehensive utilization.
Highlights
Corona discharge is widely used as atmospheric ionization sources in the applications of plasma medicine [1], [2], plasma-activated water [3], plasma-liquid interaction [4], [5] and other industrial areas [6] due to its flexibility, efficiency, and economy
When the high voltage is applied on the wire electrode array, an enhanced electrostatic precipitation effect is showing on the evolution of water droplets
With the increase of the applied high voltages, the electrostatic precipitation effect is enhanced, which manifests in the increase in the falling rates of droplet density
Summary
Corona discharge is widely used as atmospheric ionization sources in the applications of plasma medicine [1], [2], plasma-activated water [3], plasma-liquid interaction [4], [5] and other industrial areas [6] due to its flexibility, efficiency, and economy. We further studied the effect of charge on condensational growth of droplets through experiment quantitatively and found that charges alone are hard to support the growth of formed droplets in macroscopic [20] We attributed this to the synergistic effect of charges and the electric field induced by corona discharge and thought that the collision-coalescence dominates significantly in the process of droplets growth. To reveal the mechanisms underlying these phenomena, the space charges density and the number of charges carried by submicron droplets are measured by Air Ions Counter (AIC) and Electrical Low Pressure Impactor (ELPI), respectively Based on these available charging data, forces of charged droplets are analyzed to figure out the motion status of droplets in various sizes. Relative contribution of charges and electric field strength on the induced growth of the larger droplets is figured out
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