Vortex tubes have always puzzled me. They are very popular in industrial applications, their performance can be modeled to an extent, but no one knows for certain how they work. Wikipedia states "Pressurized gas is injected tangentially" but I have found this is not always the case which leads me to believe that most of the theories that involve angular momentum are incorrect. http://en.wikipedia.org/wiki/Vortex_tube#Efficiency They seem to have no limit of operation either, as they can even be used for cryogenic applications. Does anyone have an insight as to how these thing work? I wish I had the time and money to build one that has a translucent structure so I could track the flow of the gas inside.