Posted by Morris Dovey on April 20, 2009, 4:08 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.
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.
Surface area, mass, air velocity, temperatures, and heat capacity are
the variables, and all seem to be important.
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.
DeSoto, Iowa USA
Posted by Curbie on April 20, 2009, 6:08 am
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).
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.
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,