Hybrid Car – More Fun with Less Gas

Anybody know where to get a small steam turbine? - Page 9

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Posted by Tim Jackson on March 27, 2009, 8:20 am
Don T wrote:

I'm not saying that copper is particularly good for this application,
I'm just saying it's got a higher reflectivity at fIR than at optical
wavelengths, and not many materials do.

Yes you can improve any good IR reflector's ratio by applying an
optically absorbent layer that is thinner than the emitted wavelength.
Someone mentioned for example blackened nickel - that should work, so
should silver, but you have be able to ensure the layer is thin enough
not to raise the fIR emissivity, not much more than a micron.


Posted by Tim Jackson on March 29, 2009, 5:22 pm
Don T wrote:

Here is a picture of the offending if not offensive item - my
grandmothers old silver teapot - I tracked it down.  The inside hasn't
been cleaned for decades (she died in '87 & I don't think it's been used
often since).  The inside of the *lid* got polished nicely though.


Incidentally I've got a Russian samovar that looks pretty much the same
inside, and that's just limescale.  So I imagine this is tea-stained


Posted by Curbie on March 26, 2009, 4:57 pm

Over the past 30 years McDonnell Douglas, Power Kinetics, the Jet
Propulsion Laboratories, Sandia National Laboratories, Cummins Engine
Company, SunLab, and others have all big buck wacks at EXACTLY this
idea "Solar powered Stirling". All have engaged members of BOTH
physics and engineering communities, having varying degrees of success
none of which was commercial.

I knew all this before I spent a huge amount of time playing with this
idea, it did stop me and I hope it won't stop you. Most discoveries
come from people who are not looking for exact thing they find, who
knows what you'll find by trying, for certain, you'll find nothing by
NOT trying. I just think your going to have to scale-up your collector
or scale-down your output power expectations.

But who cares what I think (or anyone else), keep the costs down, have
blast doing it, and no matter the results you'll be better off for the

Best wishes.


Posted by Morris Dovey on March 26, 2009, 7:53 pm
 Curbie wrote:

That's worth knowing - and I'll guess that the knowledge doesn't deter
me from inquiring for exactly the same reasons it didn't deter you. :)

I don't mind that (much). The original goal was to produce a
solar-powered pump that could be deployed inexpensively off-grid in
undeveloped parts of the world. At this point it appears that goal will
be met within the next few months. It /isn't/ particularly efficient,
and it doesn't qualify as a technical wonder - but it'll fill a need.

Serendipity, like fortune, passes everywhere. :) When I tried not
painting my flat panel absorbers flat black and left them shiny, the
output jumped. It was a physicist in Scotland who figured out what was
going on and who sent me off to read up on black body radiation (my head
hurt for weeks!), and by the time I'd made mods to take real advantage
of the effects, that "jump" looked almost trivial.

The large corporations /must/ focus on developments that contribute
substantially to their bottom line - and there just isn't much profit in
developing a device that a farmer without any kind of technical training
can build for himself. Hmm - or is there? Maybe we need to think about
that some more...

...people with full bellies and healthy families probably aren't
inclined to become either terrorists or willing victims.

Eh? I care what you think - and it makes a (positive) difference in my
result when you share your thoughts and make me re-examine my own. And
you're right, I'm a lot better off than I would be if I decided to spend
my final years in a rocking chair, puffing on my pipe, being bored out
of my (shrinking) mind.

Morris Dovey
DeSoto Solar
DeSoto, Iowa USA

Posted by daestrom on March 26, 2009, 11:01 pm


One more point about temperatures and Carnot.  It isn't how hot the outside
of the cylinder/tube gets, it's how hot the working fluid temperature gets.

Of course you wouldn't do this, but if your collector tube were made of
insulation, the outside could get 1000F but if the working fluid inside only
rises to 80F, then that would be the temperature you plug into Carnot (after
converting things to absolute).

So on the one hand you want a nice small 'collector' to focus the sunlight
on so it reaches a nice high temperature.  But on the inside of the tube you
might want a cross piece or something to increase the surface area between
the tube and the working fluid (air) inside.  The name of the game is
getting the heat from the tube into the working fluid as quickly as


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