Enhanced Growth of Single Droplet by Control of Equivalent Charge on Droplet

The presence of charges on droplets and aerosol particles can increase collisions among these objects, which would ultimately have effects on precipitation and cloud over. The traditional experiments on the effects of growth of charged droplet have deficiency in that the charge of droplet was not accurately controlled. In this paper, better control of equivalent charge on a single droplet was realized by changing the voltage applied on the stainless steel needle whose tip was used as the condensation nuclei of the droplet. The breakdown voltage at the tip of the stainless steel needle (radius 1 μm) was 2000 V at the humidity of 98± 2% and temperature of 3± 1 °C. Voltage of less than 700 V could not lead to corona discharge, which further guarantees the accurate control the charge of droplet. Increasing equivalent charge of the droplet not only increased the growth rate of the droplet, but also increased the eventual size of the droplet. The electric field of 1.9 × 10
⁷
V/m at the edge of the droplet was found to be the threshold for the growth of charged droplet under this experimental condition. The calculation of collision rate coefficient between the charged droplet and aerosol particles suggests that the contribution of electric force to the growth of droplet was at least three orders of magnitude higher than that of thermophoretic and diffusophoretic forces when the charge of the droplet was greater than 1.43 × 10
⁵
e.