Ah, I finally found it, including the full show. If anyone is interested it was Science Shack with Adam Hart Davis. I've not rewatched the show but I guess it was either the heat pump or the vortex tube...
http://en.wikipedia.org/wiki/Vortex_tube
In 1988 R.T.Balmer applied liquid water as the working medium. It was found that when the inlet pressure is high, for instance 20-50 bar, the heat energy separation process exists in incompressible (liquids) vortex flow as well.
I hadn't heard of this before, interesting stuff!