Heat engines in practice

From: Y. T. (ytyourclothes_at_p.zapto.org)
Date: 08/20/04 

Date: 20 Aug 2004 15:18:33 -0400

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.

Here at the border of southern CA and AZ, for example, we get a whole
lot of solar energy during the course of the day. If this was used to
heat some tank full of oil and run a heat engine between the hot oil
and the cold night-sky, it appears one could generate a decent amount
of electricity from solar irradiation even during the night. Obviously
such a system should be designed such as to use the minimum amount of
storage fluid possible (to get the maximum temperature for a given
amount of energy which will yield the best carnot efficiency upon
back-conversion). However there's also the question of thermal losses
- which will increase with increasing temperature (but also decrease
with decreasing volume (better:surface)) of the storage medium.

If I figure using 10000sq ft (i.e. 1000sq m) for gathering solar power
at about 1kW per sq m that would be a megawatt of input - and if I
could get only 1/10 of 1 percent efficiency total out of this it would
be 1kW which is more than we're actually consuming right now in the
month to month average.

In order to do even the simplest back-of-the envelope calculation,
however, I need to know how cool my storage medium could get and still
allow me to run a heat cycle from it at all - efficiency be darned for
the moment.

Is anybody in the world doing research on this kind of thing? Trying
to get electricity out of smallish temperature differences? What's the
state of the art?

If there's one thing we have in the desert here then it's large
useless areas with nothing but sun shining on them and as much as I'm
looking forward to getting out of the desert this fall (college) it
seems that there's this resource here that is completely unused...

cordially

 Y.T. 

--
Remove YourClothes before you email me.
http://p.zapto.org/yt

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