Hybrid Car – More Fun with Less Gas

Anyone interested in building cheap DIY parabolic troughs? - Page 3

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Posted by Morris Dovey on November 14, 2008, 5:28 pm
azuredu wrote:

At the tuning tube, where there's an alternating positive/negative
pressure. The pump diagram at


should help you to immediately grasp the idea. Let me invite you to
browse through the pages with links at


(the pages are all fairly short) so you can get a more complete picture.

In fact, please feel welcome to browse the entire site - that's why it's
there. :)

Morris Dovey
DeSoto Solar
DeSoto, Iowa USA

Posted by azuredu on November 14, 2008, 4:35 pm

I should tell you that I also have a cheap thermal storage solution
(high temperature, 200C+). So if you have a working heat engine, you
may get round the clock electricity generation and so on. A real
solution to global warming.

But I have some worries about the efficiency of such engines.

Posted by Morris Dovey on November 14, 2008, 5:48 pm
 azuredu wrote:

I've bookmarked your home page. Right now my focus is on the engines
themselves. (But thank you.)

The efficiency depends on the temperature difference between the hot
head and the cold head. At 325C there's a theoretical limit around 55% -
which is good compared to current PV conversions.

These engines are only suitable for a limited subset of applications,
but I'd be happy to produce solar solutions to only a few of the world's
problems. :-)

Morris Dovey
DeSoto Solar
DeSoto, Iowa USA

Posted by azuredu on November 15, 2008, 5:56 am
Here's my first suggestion for your fluidyne.

You could replace the open tube by a closed chamber with elastic
walls, such as a bellow. The moving wall of the chamber then will
allow you to output mechanical work, without friction.

Of course you'll have to translate oscillatory movement into rotation,
and fight for the material's wearability.

Moreover, when the whole system is closed you can increase internal
pressure to gain output power.

More suggestions will come later. I have got the impression that your
design is not very optimised. By the way, I suppose that you know that
the best working gas is helium?

Posted by Morris Dovey on November 15, 2008, 10:35 am
 azuredu wrote:

Yes, friction will require work to overcome - but it also takes work to
deform an elastic wall.

Why "of course"? I'm perfectly happy with linear oscillation.

I wish that were so, but output power is determined by the input power,
and efficiency is determined by the hot/cold head temperature
differential. The most effective way to increase output power of a
reasonably efficient engine is to increase input power. In this case,
that would mean increasing the capture area of the solar trough.

We are optimizing different things. You seem to be maximizing the device
efficiency, and my objective is to maximize availability of benefit with
efficiency as a secondary consideration. We aren't exactly at
cross-purposes, but neither are we trying to solve the same problem. :)

Having said that, let me emphasize that your suggestions are appreciated
  and that I am still /very/ much interested in ways to build
inexpensive parabolic troughs, mounts, and tracking systems.

One additional note - I have a practical algebraic two-surface challenge
that, of all the people I've met, you might best be able to solve. If
you're interested, I'd be happy to pass it along. I've attempted an
intuitive solution, but I'm sure it's sub-optimal. :)

Morris Dovey
DeSoto Solar
DeSoto, Iowa USA

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