you want this
not sure where the charts are if they are anywhere still (they generally escape even the internet archive)
http://forums.procooling.com/vbb/pri...2&page=1&pp=25
most of your "cold" range heat transfer fluids are going to be hydrocarbon based
I did considerable research into this about 4 years ago (which is about as old as that thread cited )
the expensive Perfluorocarbons are really the best solution, but as you have mentioned, sealing against them, the expense is tough, I actually have some pics of the stainless steel plumbing on the Cray that used to be up at NCAR. Unfortunately they are on a RAID array that is currently offline.
Methanol's drawbacks as both flammable and toxic require nearly the same level of plumbing and precautions that make the flurocarbons such a pain, I came to the conclusion - in for a dime in for a dollar
there are also brine solutions but not as low as your talking about
methanol is a solution but with different tradeoffs
expand your searching to spray cooling
and dual phase change microchannels
that might be the justification youd need to go back to Perfluorocarbons
the trick is finding a pump, getting the plumbing done and making it a totally closed system that doesnt have evaporative issues.