Effects of liquid conductivity upon gaseous discharge of droplets

The effect that liquid conductivity has upon gaseous breakdown and conduction between a droplet and a sharp grounded metal point was investigated as a function of the droplet charge level and point-to-droplet gap. A uniform stream of equally spaced 1210 μm droplets was studied in passing the point at 2.05 m/s at a rate of 465/s. The negative droplet charge was set at 24, 40, 55, and 60% of the Rayleigh hydrodynamic instability limit (i.e. 3×10^-10 C) for liquid conductivity values in the 10^-4-10¹ S/m range characterizing electrostatic crop sprays. No significant conductivity effect was found for charges up to the 55% level; the most conductive liquid exhibited a significantly (α<0.10) higher discharge current at the 60% charge level. For close gaps, droplets departed the grounded point region with a reversed charge, indicating they were overneutralized by a positive-ion flux from the grounded point