Synergistic effect of charges and electric field: water droplet condensation and coalescence in a sub-saturated cloud chamber

In nature, the condensation, coalescence and growth of water droplets have a crucial positive effect on the process of cloud formation, which is hard to occur under a sub-saturated environment. In this paper, the growth of water droplets is detected in a 0.24 m3 sub-saturated cloud chamber with unipolar corona discharge and needle electrode configuration. The results show that the diameter of water droplets can grow up from submicron to 32 m under −39 kV at relative humidity ∼85% and ambient temperature ∼10 °C. The growth mechanism in the evolution process is further discussed, focusing on the effect of charge on charged droplet condensation, and the synergistic effect of charges and electric field. The former is verified by the comparison of experimental average net charges of some typical diameter droplets and minimal charges needed to maintain self-growing. The latter is demonstrated by the analysis of charged droplet motion and the ionic wind recorded by a camera. The analysis is in good consistency with the experimental results, which suggests its promising and potential applications in the utilization of atmospheric water resources.