Posted by Morris Dovey on April 20, 2009, 4:08 am
Curbie wrote:
> Generally speaking since Stirlings operate of the heat difference
> between hot & cold I think anything that expels from the from the cold
> side and keeps heat in the hot side, with the only path for heat to
> escape is through the regenerator on to the cold side will make an
> efficiency improvement.
Mostly true, except that heat escapes everywhere. On the four-incher, we
actually wrapped both the hot head and the regenerator with fiberglass
batting, and it does improve performance. It's not in the photograph
(made before the insulation was added) because it would conceal a lot of
what it's helpful to show.
>>> 3) Are you using copper scouring pads Chore Boy or the like in
>>> the regenerator?
>> I'm using bundles of thin brass tubes.
> Have you played with scouring pads, Chore Boy make in copper if I
> remember?
We haven't - primarily because we're trying to work toward avoid
reproducibility issues and having the copper blown from the regenerator
into hot or cold head - or worse, jammed into one of the elbows at
either end of the regenerator.
With the thin brass tubes, it's much easier to quantify the parameters.
> Total area & type (copper, aluminum, ...) of regenerator material
> seems to determine volume of heat stored, while the thickness of
> regenerator material seems to determine the rate of the material's
> heat transfer. Both are important.
Surface area, mass, air velocity, temperatures, and heat capacity are
the variables, and all seem to be important.
>> Simon Popy assembled his second engine with a PVC pipe jacket on the
>> cold head so he could give the idea a try. I don't think he's actually
>> circulated water through it yet.
>
> Well, you can beat yourself to death over fractions of a percent of
> engine efficiency, but sooner or later you're going to have to put the
> torch down and get the best design you have to run on solar heat.
Ok :) Did that this past Friday with the 4x8 parabolic trough with
oh-hum results. I think I know why the displacement was disappointing,
and it'll take yet another rebuild to correct the suspected shortcoming.
FWIW, non-solar heat (from a heat gun, hairdrier, torch, etc) allows
much more productive use of time - and in the case of the parabolic
trough, even the torch is safer.
We're a long way from the point where we'll be worrying about tiny
increments of efficiency.
--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/
Posted by Curbie on April 20, 2009, 6:08 am
>Mostly true, except that heat escapes everywhere. On the four-incher, we
>actually wrapped both the hot head and the regenerator with fiberglass
>batting, and it does improve performance. It's not in the photograph
>(made before the insulation was added) because it would conceal a lot of
>what it's helpful to show.
Seeing the design was very helpful, heat migrating from the hot to
cold sides via the (water) piston/displacer is inevitable by design. I
think the goal is to make it as easy as possible for heat to enter the
hot side AND to transfer into the Working Fluid (air), sounds like
potentially another tube-like heat exchanger here, then capture what
is practical with the regenerator, and reverse process on the cold
side with a water-cooled heat exchanger.
For both hot-side and cold-side heat exchangers I would be thinking
"Regenerator", I think you'll see best result if think "getting the
heat in and out of Working Fluid" (air).
>We haven't - primarily because we're trying to work toward avoid
>reproducibility issues and having the copper blown from the regenerator
>into hot or cold head - or worse, jammed into one of the elbows at
>either end of the regenerator.
Makes sense, in that case I would think about three "regenerator-like"
structures hot, cold, and regenerator with the primary difference
being the regenerator is hampled (bast as pracical) from transferring
heat to the outside of the engine.
>FWIW, non-solar heat (from a heat gun, hairdrier, torch, etc) allows
>much more productive use of time - and in the case of the parabolic
>trough, even the torch is safer.
I agree with you safety concerns and I hadn't considered a heat-gun,
an idea I really like if the heat it produces can be controlled to
mimic the performance of the collector
When I was digging through my Stirling back-up, I did run into my
notes on what I felt were the problems with Stirlings which didn't
include a Fluidyne, between the "Solar Bowl" idea inspired be Ulysses
and your work on the Fluidyne, I may take another look at the numbers,
some time.
Good Luck.
Curbie
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> between hot & cold I think anything that expels from the from the cold
> side and keeps heat in the hot side, with the only path for heat to
> escape is through the regenerator on to the cold side will make an
> efficiency improvement.