alt.energy.renewable

daestrom wrote:
>
> "Morris Dovey" wrote in message
> news:47FA1F1C.B502DEF@iedu.com...
> > Bruce Richmond wrote:
> >>
> >> On Apr 6, 7:14 pm, Morris Dovey wrote:
> >> > daestrom wrote:
>
> >> I saw your web page about building the fluidyne engine a while back
> >> and after reading the mention that it was a Stirling engine didn't
> >> give it any more thought to the details of how it works. I Know how
> >> Stirling engines work so that was a I figured I needed to know. But
> >> after looking again I realize the principals may be the same but the
> >> details are different.
> >>
> >> The diagrams shown are close to the standard ones but are still a bit
> >> confusing to most that see them the first time. The reason I say
> >> close is that line 2-3 on the p-v chart should be shorter than line
> >> 4-1. With them the same length you have the same heat going out as
> >> coming in and no energy going out as work.
> >
> > Umm, yes. Sometimes it's amazing how obvious some things are
> > after someone else points 'em out. :-) Thanks.
> >
> > Methinks I need to begin thinking about some P/V/T
> > instrumentation for these things - about a year or two ago. Ouch!
> > - nothing I have comes close to fast enough for sampling in real
> > time.
> >
> >> http://www.cse.iitk.ac.in/~amit/courses/371/abhishe/main2.html
> >
> > That looks more reasonable than what I drew. I'll redraw.
> >
> >> Your explaination of the rise in air pressure pushing the water down
> >> on the hot side doesn't agree with the diagram either. While it takes
> >> pressure to push the water down, the chart shows the pressure
> >> decreasing from 1-2. Actually the chart shows the pressure rise from
> >> 4-1 with the volume held constant. The volume is then allowed to
> >> expand from 1-2 while more heat is added to hold the temp constant,
> >> despite the drop in pressure.
> >
> > Good. This was an area of uncertainty for me as I wrote. When
> > I've finished writing this, I need to spend a bit of time
> > re-reading and and digesting this.
>
> The water going 'down' on the hot side *does* occur while the pressure is
> rising. This is line 4-1. But the water in the *outlet* tube doesn't rise
> until you get to line 1-2. You have to understand that the water in the
> three columns are not oscillating 'in phase'. The 'power stroke' is from
> 1-2 and that is when the 'outlet tube' water level is rising. But the water
> in the 'hot side' is BDC at that point (i.e. it already dropped during 4-1).
>
>
> >> You mention the regenerator when going from 2-3, but a regenerator is
> >> not a required part of a Stirling engine. It does improve efficency
> >> and is worth explaining how it does so, but it need not be included in
> >> the basic operation explaination.
> >
> > Ok. We've used a copper tube to connect the hot and cold head.
> > Originally bare, we've wrapped it in insulation - and it does
> > appear to affect the operation of the engine. I'll move
> > regeneration from basic operation to another discussion of
> > "enhancements". Good point.
>
> I wouldn't. The regenerator is a key part of the Stirling cycle. Without
> the regenerator, you have something more like a Brayton cycle. The
> displacement periods (4-1 and 2-3) would have no temperature rise at all
> (i.e. line 4-1 shrinks to a point, as does line 2-3). And the expansion
> (1-2) is no longer isothermal but a rising temperature and 3-4 becomes a
> falling temperature/compression. There isn't a formal name for it in
> thermodynamics, but it ain't Stirling anymore.
>
> >
> >> You also wrote, "at maximum engine volume". Normally a Sterling
> >> engine is a closed system, so the volume of the engine as a whole does
> >> not change. In the fluidyne engine you have built the right hand tube
> >> is open to the atmosphere, so I suppose you could say it changes
> >> volume as the fluid moves up and down in the vented tube.
> >
> > This is how I saw it and found a similar description. With the
> > most recent changes we're seeing a 9-inch periodic variation in
> > the height of the water in the open tube, which really does look
> > like a volume change.
> >
> >> One of the ways to increase efficiency in a Sterling engine is to
> >> increase the pressure of the working fluid. The higher density of the
> >> gas allows faster heat transfer. Have you tried having the water level
> >> in the open tube higher than in the other two? That would raise the
> >> pressure of the gas trapped in the closed loop.
> >
> > We have, but the improvement in performance seemed fairly small.
> > OTOH, partially blocking the opening seemed to produce a larger
> > improvement, which may have bearing on your point.
>
> See my other post about 'tuning' the output column to get the right phase
> shift between output column and the 'hot side' column. Best performance is
> when you can get them 90 degrees out of phase. When the hot water reaches
> 'BDC', you want the outlet to be midway between BDC and TDC on its way up
> (i.e. the 'power stroke')
>
>
> >
> >> For 3>4 you write, "The cooled air is compressed in the cold head, and
> >> heat Qc is sunk to the cold head at constant temperature Tc.
> >> Consequently, the engine volume decreases, while the engine pressure
> >> increases." Again, the lower temp contributes to decreasing the
> >> volume, but in doing so it would decrease the pressure, not increase
> >> it. The increased pressure comes from mechanical means. In a normal
> >> Sterling engine a flywheel, connecting rod and piston provide the
> >> mechanism. For the fluidyne engine the water is the piston and its
> >> motion in the tube provides the temporary storage and return of
> >> mechanical energy as a flywheel does.
> >
> > Yuppers. The water appears to act as a simple pendulum that
> > "swings" between the hot head and the open tube. One of our two
> > biggest challenges is to match the natural frequency of the heat
> > cycle to the natural frequency of that pendulum.
>
> Yep. That's the 'tuning' I refer to. Ideally the water does *not* act as a
> simple pendulum between hot and open tube, but has a short of phase shift
> between them. Either a restriction or add/subtract water in the outlet tube
> in small amounts until you get maximum swing.
>
> As far as 'outlet', the 'open tube' is the output point for the engine. It
> is commonly used to pump water, but I suppose other uses could be devised.
> The problem with closing it off or putting some sort of 'turbine' in it is
> the variation in load will affect the tuning.
>
> daestrom

If adding load is going to change the "tuning" in order to get any
efficiency out of it seems like some sort of feedback is
going to have to be introduced to keep it in tune...

Can not think of any way to do it at the moment..maybe some sort of
bellows to close off the tuning column....driven by pressure
from the the top horizontal...need to make it self tuning....
a balloon maybe...??

have fun.....sno

pressure