Right now, the system consists of separate air and coolant lines, which converge pretty much right at the nozzle. Ideally, I'd want a system that shoots a narrow solid cone of air, with a slight stream of coolant in the middle. That way, the air has some spread to blow away chips, while the coolant is more directly aimed at the tool bit.
I made a concentric nozzle, where the air nozzle is just the usual loc line nozzle with 1/8" opening, and about 1/4" inside of this is a small nozzle for the coolant. There are separate valves for air and coolant.
The main issue is how can I determine whether the coolant is coming out as micro-sized droplets, or as a completely atomized mist? I've read that the latter is bad since it tends to fog up the shop and you end up breathing it.
Based on some reading, it seems that what makes this difference is the configuration of the junction (something about meeting at right angles and particular sizes of the air and coolant junction, as based on posts trying to replicate the Bijur spray mist system) and also something about the coolant being pressurized vs getting sucked out by the Venturi effect. The latter reason makes no sense to me because the valve is downstream from the pressurized coolant, and if you try to use that to regulate flow, then it will take all the pressure drop, and the coolant at the nozzle tip gets "sucked out" anyway.
Short version of my questions:
What's a good nozzle design to achieve the effect I want?
How can I tell if the mist is overly atomized?