Investigation of the evolution of the charged water droplets in the electrodynamic trap

摘要

Water droplets of radius between 1 and 20 μm carrying electric charge were individually contained in an electrodynamic trap. The trap was kept in a small climatic chamber, which enabled imitating the temperature and humidity conditions of the lower troposphere. The sign of the charge of the droplet could also be controlled. For the humidity close to saturation, droplet injected into the trap was evaporating for a few seconds and could either undergo a Coulomb explosion and escape from the trap or stabilize at the size of few μm. In such case, the final droplet radius depended on the value of the droplet charge and of the humidity. The evolution of a trapped droplet was investigated by means of scatterometry. A numerical model of such evolution, incorporating the kinetic effects near the droplet surface was constructed. By fitting this model to the experimental data the evaporation coefficient was found to be 0.14+-0.04 in average. Possibly a dependence of this coefficient upon the value of the droplet charge was found. An explanation of such dependence is suggested. The significant influence of the droplet charge upon the evolution of small water droplets seems important for the detailed microphysical description of clouds.