Imagine your wort chiller, only made from stainless. Thats what I have, but the stainless has a heat conductance of about 1/10th of copper. ...
1/10th is way off. SS will be more like 94% as efficient as copper in that same design.
I see a lot of confusion and misinformation when it comes to thermal issues.
The main thing that many people miss is that we are usually talking about a
system. In this case, a
system of tubing (length, radius, wall thickness, thermal properties, etc), a coolant liquid (temperature, thermal properties, flow rates, turbulence, etc), and the warm liquid. Just quoting a thermal conductivity spec for one component does not tell you much (if anything) about how that affects the performance of the
system.
As mentioned a few times above (Hermit & bendavanza), the thinness of the SS helps to offset the lower thermal conductivity of SS versus copper.
But the bigger point is, the thermal conductivity of the material is not really a major limiting factor in immersion chiller design. I ran some numbers once, not sure I could find them now. Larger diameter tubing can help because you have more cold surface, only a small part is due to the increased thermal conductivity with more material.
In short, using a material with 10x of some performance number does not mean 10x the performance in the system (or even 2x, or 1.1x).
Plug a night light into a 6 foot extension cord. Now plug it into the same gauge 12 foot extension cord. It won't be half as bright, it won't even lose 1% of its brightness, even though the electrical conductivity has been cut in half. Because the electrical conductivity of that extension cord is not the limiting factor in that system. Gotta look at the whole system.
edit: for reference -
http://www.engineersedge.com/properties_of_metals.htm
Copper is over 20x 'better' at conducting heat than the same thickness SS. Important if that is your limiting factor.
-kenc
