Measurements of the velocity of ink jet droplets were made using a microscope in an experimental apparatus in which the nozzle is about 18 μ m in diameter. It was shown that the distance for the coalescence of droplets from the liquid jet increases with the increase of density of liquid.
The equation of motion for the droplet is analyzed numerically by assuming the air velocity around a droplet, and trajectories are obtained. The results of numerical simulation for the coalescence correspond to the experimental results well. It is pointed out that the droplet stream stability is affected by the surface tension of the jet.