[ExI] is our friend somehow involved in this?

spike spike66 at att.net
Sat Dec 5 00:46:27 UTC 2009


 


Hi friends, note the change in subject line.  If someone puts their own name
in a subject line, that is fine.  For privacy reasons and established
protocol, unless you have specific permission from that person, do eschew
putting anyone's name in a subject line thanks.

> ...On Behalf Of Henrique Moraes Machado
> ...
> 
> Not being an engineer myself, I had to go to wikipedia to try 
> and have any idea of what you're talking about... Ok. It's a 
> Stirling engine...

Well it can be a Stirling engine, but that isn't exactly what I have in
mind.  I was thinking something analogous to a steam turbine cycle, except
instead of water, we might use a higher temperature working fluid such as
mercury or some other metal.  With that big a concentrator, we have really
high temperatures at our disposal, and recall that we need to actually boil
the stuff and recondense it.  

Likely water wouldn't do for this application, because it cannot be
condensed at temperatures below about 650K (if I recall correctly, somewhere
in the 600s I am pretty sure).  Mercury is up in the 1700s, so I could
imagine the heat source at a couple thousand K and the radiator exit at
about 700 to 800-ish, allowing a theoretical efficiency higher than you can
get with PVs.

> ...but isn't heat dissipation a big 
> problem in a vacuum? 

We get rid of the heat via radiation to cold space.  It is a big problem,
but there is a big solution to go with it.  If we are talking about a km
diameter mirror, then we are also talking about a biiig radiator.  If we can
run at high temperatures as we likely would for this application.  Heat is
radiated out into space as a function of temperature to the fourth, so
depending on how it is scaled, dumping heat in space is easier than it is
down here on the deck.  Down here of course we use the heat of vaporization
of water with the big cooling towers.  But in space, if sufficiently scaled,
a radiative condenser would be great.  It is a space engineer's playground!

Of course none of this will generate energy as cheaply as burning coal down
here, I am not claiming it is, unless it is scaled to a really remarkably
big station.  I don't think our friends at Solaren can do it either, but if
they manage to pull it off, I am cheering wildly for them, and will gladly
tell the whole world I was wrong.

spike







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