How does a spray cloud behave?

Spraying is important for many applications, from medication administration and disease propagation to pesticide use in agriculture, it is always important to know how and to what extent spray clouds form, propagate and disappear. We use nozzles with micrometric holes to produce water sprays, and record the cloud propagation with time for different spray speed. We find that the shape remains the same, but the propagation distance of the cloud varies greatly with the speed. We also change the salt concentration in the water to provoke friction induced charging of the droplets. Doing this, we obtain repulsion between droplets, which drastically limits coalescence and changes the droplets size. We notice an important change of behaviour between a charged cloud and a non charged cloud. Since droplet size seems to have a great effect on the cloud behaviour, we then measure the droplets size within different spray clouds and multiple configurations. We remark some coalescence effects increasing the droplets size, followed at a greater distance by some evaporation decreasing the droplets size. Since we still observe droplets far from the nozzle, we conclude that the cloud disappearance for the naked eye is due to the low droplet density far away from the nozzle and not evaporation.