Dr. Lee,
I have been reading the Aeroturbo muffler topic in the 6.5 TD forum. That topic was in danger of becoming a geek-fest, so I brought that part of it over here.

I deal with a company named Exair.com and they have a fascinating device called a vortex tube. Go to their website and read the background on that (Products/Vortex Tubes/Vortex Tubes/Theory and History). It's quite fascinating. Simple plant compressed air goes in, and a hot stream comes out one side and a cool stream out the other. Seems to challenge Thermodynamics , or at least push it a little bit. It seems to split the thermal energy of the input mass. Just read it.

Could this vortex science be applied to a muffler design? Exaust the hot fumes to the tailpipe and send the cool fumes to a PMD cooler :^)