Electrohydrodynamical behavior of charged droplets in air and its coalescence

To improve the quality of characters printed with an ink jet printer, the effect of aerodynamics on the trajectories of the charged droplets must be taken in account. Experimental results showing that the drag coefficient for the train of droplets is much smaller than that of a single droplet are reported. The ratio of the drag coefficient of the train of droplets to the Stokes' resistance was about 0.5-0.65 for a frequency of about 80 kHz. This ratio seems to change with the droplet separation, initial velocity, and other factors. It was also found experimentally that the observed coalescence of droplets during their transit from a nozzle to a platen depended on various parameters. In general, coalescence occurred when the droplets were highly charged.<>