alt.energy.renewable

>
> "Bruce Richmond" wrote in message
> news:30d7981e-3e52-4932-b1be-24108830f526@u69g2000hse.googlegroups.com...
> On Apr 9, 4:31 pm, "daestrom"
> wrote:

> >
> > According to "Engineering Thermodynamics with Applications" (Burghardt),
> > "A
> > regenerator is the key element in both cycles [Stirling and Ericsson];
> > heat
> > must be stored in the regenerator during one part of the cycle and
> > reused in
> > another part."
> >
> > Ideally, the regenerator heats the gas all the way up to the hot-side
> > temperature and the heat source only inputs enough to maintain the gas
> > temperature during the expansion. Similarly, the regenerator cools the
> > gas
> > all the way to the cold side temperature and the heat sink only rejects
> > the
> > heat of compressing the gas. Of course unless you have an 'infinite
> > regenerator', this can't happen in the real world and there is
> > additional
> > heat added /rejected by the source/sink.
> >
> >
>
> A regenerator may be a key item in getting a Sterling engine to work
> more efficiently, but it is not a mandatory item. The example I
> provided when explaining how a Sterling engine works did not have a
> regenerator.
>
> http://www.cse.iitk.ac.in/~amit/courses/371/abhishe/figure3a.gif
>
> This old Ericsson doesn't have one.
>
> http://rustyiron.com/engines/stable/ericsson.html
>
> There is none in this basic Sterling animation
>
> http://www.flying-pig.co.uk/mechanisms/pages/stirling.html
>
> Obviously this engine works better with a regenerator. My point was
> that if it isn't required to explain the basic operation it would be
> better to handle it seperately.
>

Maybe we're splitting hairs here, but the key item that makes a 'Stirling
cycle' engine a 'Stirling cycle', is that the heat must be added at a
constant temperature and the movement from cold to hot and hot back to cold
occur with a constant volume (i.e. the gas pressure rises/falls as the gas
moves from hot to cold to hot (process 4-1 and 2-3). You can't do have
isothermal expansion/compression unless you have a regenerator that heats
the air up to T-hot *before* it enters the heater and cools it down *before*
it enters the cooler.

The iron cylinder and displacer *do* in fact act as a crude regenerator. I
have a nice 'toy' version where the displacer is actually a porous mesh
material. As the displacer moves between the hot and cold cap, the air
flows 'through' much of the displacer/regenerator and thus is pre-heated /
cooled by the mesh. Those early models that use a metal 'displacer' are
also functioning as regenerators.

Another standard 'air-cycle' engine is one invented by John Ericsson and is
named for him. While both the Stirling and Ericsson cycles ideally perform
the compression and expansion under constant temperature conditions, the
Ericsson cycle adds the heat under constant pressure instead of constant
volume (on the P-V diagram, process 4-1 is a horizontal line instead of
vertical one and process 2-3 is as well but the line 2-3 is much longer than
4-1).

Of course in reality no 'real' engine attains the 'ideal' case of expansion
and compression at a constant temperature. And in reality neither constant
pressure or constant volume can be maintained while the displacer moves the
gas from one side to the other. So the lines are blurred between Ericsson
and Stirling cycles.



> > There are several 'odd' thing about the fluidyne versus other Stirling
> > cycles. The water column on the far right that is open at the top is the
> > 'output' of the engine. It rises and falls as the gas pressure rises and
> > falls within the loop. As this water rises, you would call it the 'power
> > stroke' and as it falls, the compression stroke where the potential
> > energy
> > of the column does work on the gas to compress it.
> >
> > Although his video can't show the water column in the 'hot' side, if you
> > could see inside the heater, you'd find the water level in it does not
> > rise/fall as much as the outlet tube. But it does rise/fall more than
> > the
> > water in the cold side. And it isn't in 'phase' with the cold side.
>
> From what I could see the water in the cold side was hardly moving.
> Last I knew water didn't compress much, so the volume in the outlet
> tube has to be going somewhere. Since the hot tube is about the same
> diameter as the outlet tube I figured the water in it must be going up
> and down nearly as much as in the outlet tube.
>

Yes, I 'misspoke' before. Sorry 'bout that. See my other reply.


>
> How do you propose to extract work at the outlet tube? I think some
> might get the impression that this engine could pump water roughly
> equal to the volume that is sloshing back and forth each cycle, but
> that is not the case. The displacement of the water reaches that
> level because it is moving at a harmonic frequency of the system. It
> can do a small amount of work each cycle and the amplitude of the
> motion will stabilize at some level lower than it does with no load.
> But if you try to take too much energy out it will just stall the
> action.

Quite right. These systems are often used for pumping water. One diagram
I've seen took the output tube and fed it to 'largish' chamber with
check-valves leading in/out. As the fluid surged in/out of the chamber, it
moved water in one check valve and out the other. Yes, obviously this extra
'load' affects the 'stroke' and cycles per minute (CPM???).

The appendix in this article (PDF page 25) discusses the 'liquid piston
Stirling engine'. But I should warn you, this article must have been
translated or something, some parts the spelling is wild. (written in Oak
Ridge, Tenneosee[sic] )
http://www.ornl.gov/~webworks/cppr/y2001/rpt/27113.pdf

daestrom