Hello Jim,
I looked into the Hilsch Vortex tube a while back. It is basically a refrigerator or heat pump using the energy of the air pressure to convert or separate the air into two temperature zones. As a cycle though, I don't think the efficiency is high enough to be useful. Possibly the exhaust steam from an engine could be used to run the thing, in which case we would get some cool saturated steam and some hotter superheated steam in the mix. It would be better to expand the steam to do work though if possible.
However, a Unaflow engine does have to exhaust steam at higher than atmospheric pressure to move the steam through it. This steam might be used to do two things using a vortex tube. The first would be to pass the cooled steam to the condenser to condense that part and the second would be to use the hotter steam to heat the feed water for some regeneration. This then might add a point or two to the engine efficiency.
Best, ------ Bill G.