alt.energy.renewable

"sno" wrote in message news:47FD2EE3.12BF3EA@opelc.com...
>
>
> 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
>

It's most common application is pumping water a fixed height. So the 'load'
is fixed and can be considered in the 'tuning'. But other applications
could be more problematic.

daestrom