Just a thought, I dont know if it would even work. A company called Nitrous Oxide Systems makes a NOS nozzle much like you just described. Its purpose is to mix the fuel and NOS right before it comes out of the sprayer.
Here is a link to what I am talking about.
http://www.holley.com/HiOctn/ProdLin...13700RNOS.html
It prolly wont work for what you need but maybe it will help with the design process.
NOS objective is the same as yours. To create the finest mist possible.
Hope this helps a little.