Re: Heat engines in practice

From: Uncle Al (UncleAl0_at_hate.spam.net)
Date: 08/20/04 

Date: 20 Aug 2004 15:32:57 -0400

"Y. T." wrote:
>
> Not entirely sure if this should go here or somewhere into
> sci.engr.something but it strikes me as a research thing, so I'll send
> it here.
>
> What with the current global situation with regards to energy, it
> appears to me that venues of generating usable forms of energy that
> are currently deemed inefficient will come more to the forefront of
> the human collective thinking.
>
> In that context I was wondering what the smallest temperature
> difference is across which anybody has ever actually managed to run a
> heat engine process in a sustained way. I understand that carnot
> efficiency goes to heck as the two heat baths approach each other in
> temperature, but that is only a matter of having enough energy at hand
> to begin with.
[snip]

Consider a thermocouple junction warmed above absolute zero (not
too difficult, that). Heat is spontaneously converted into
electricity. One could take all the beta-decay waste from
nuclear reactors and harvest its high voltage electron emission.
One could ring Lake Superior with giant Dippy Birds, tie lanyards
to their butts, and pull on generators.

<http://nicholnl.wcp.muohio.edu/DingosBreakfastClub/DippyBird/DrinkingBirdCarnot.html>
<http://math.ucr.edu/home/baez/physics/General/dippy_bird.html>
<http://science.howstuffworks.com/question608.htm>

The economics stink in all cases. You put more value in than you
could ever hope to get out. Ditto sewage batteries, hooking
generators to gym exercise equipment (close to breakeven), and
burning corn for fuel. That last one is a 70% net energy *loss,*

<http://www.news.cornell.edu/releases/Aug01/corn-basedethanol.hrs.html> 

--
Uncle Al
http://www.mazepath.com/uncleal/
 (Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
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