Fluidyne Design Info

 I am interested in making a smaller model (maybe something like 10 to
30 cm^3 in volume) solar fluidyne for pumping water and have found
some good resources on the web and in the local univ library, but
still have some questions that are bugging me, so if you have build
one that works or not I would like to hear your answers.

If I use copper pipe for most of the tubing it see to me that over
time the solar heated section of the hot pipe will conduct heat away
from this area and will warm up the cooler areas and thus decrease the
temp difference between the hot and cold sides with will decrease the
power of the fluidyne.  What kind of insulators have you used to
minimize this conduction of heat from hot to cold areas?

I would like to use water, and I understand that people have used
styrofoam, as an insulating float material to help minimize the water
from evaporating due to the high temperatures of the solar heated
air.  Have you used styrofoam, how did it work, what else have you
tried, anyone used a ceramic?

If you used one way valves to do your pumping, what kind did you use
and what did you learn?

More questions to come.

Here are some references if you dont know what I am asking about and
are curious about these fascinating devices.
Proposal
http://www.engin.swarthmore.edu/academics/courses/e90/2005_6/E90Proposal/FK_AO.pdf
Final Report - excellent design info on their experience
http://www.engin.swarthmore.edu/academics/courses/e90/2005_6/E90Reports/FK_AO_Final.pdf

http://www.midcoast.com/~nlund/engineering/engines/stirlingmanual.pdf
Liquid Piston Stirling Engines, by Colin West, Van nostrand reinhold
Free Piston Stirling Engines, G. Walker & J.R. Senft, springer-verlag

Michael

  mpate@oscintl.com wrote:

At what rate do you want to pump water, and how high do you want to lift it?


Yuppers - you will have thermal losses no matter what you do. It's
important only to maintain a significant temperature differential and
keep enough of the working fluid in the liquid state to run the engine.

If you design well, you should be able to keep the cold side close to
ambient temperature. Unless you're going for the world record in
efficiency (and cost), you'll probably be better off to settle on a
design that gets the job done at reasonable cost. Even if you /are/
going for the record efficiency, you'll still do better with the
simplest possible engine/pump as your starting point.


I read the Swarthmore kid's proposal and final report and decided that
in their academic context they lacked adequate time to do a really good
piece of research. I don't think they did badly as a lab effort for a
single course, but I'm going to suggest that you should be able to do
better.

I've been told that West's book is the classic reference, but I think
you'll discover that all you really need to build a working fluidyne is
the Ideal Gas Law.

--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/Projects/Stirling/

 

5 - 8 feet of height and rate is not that important to me right now -
more just the fascination of seeing it done

I am guessing that keeping it or enough in the liquid state is pretty
hard to do over long periods of time without stopping for cool down
and then restarting, especially with water as the only fluid.



Conduction is higher loss than radiation so if we insulate for
radiation then that leaves consultion through the strucuture or pipes
and also conduction by the moving hot fluid.

So I am guessing that using insulators or poor conductors as part of
the pipe structure is important - phoenolic was mentioned and used by
the swathmore team.

For efficiency I know to expect low single digit numbers.
The metal box company ltd of india has very high efficiency numbers
(10-15%) reported on their fluidyne but I cant find much on their
designs yet.



I think they did very good for the time they had - probably only about
1 semester and only 1 round of troubleshooting to readjust and fix
leaks etc.  Do you know if they have continued this work in 2007 and
2008?


What about tuning and keeping the correct resonant frequency match of
the displacer tube to the output tube?

Also wondering if you have tried only the serial output with a "T"
section and the two valves, or have you tried a parallel output with
the "+" section in the middle of the output tube?
I read that the parallel output may give more pumping power without
disturbing the resonance of the output tube.

 mpate@oscintl.com wrote:

It helps to know that. [*]


Actually, if you keep the cold side near ambient (I'm assuming some
reasonable "room temperature") it can help to cool the fluid as well as
the air. Of course, it'd be nice if the fluid didn't get so hot - but
from [*] above, I'd suggest not wasting a lot of effort worrying about that.


Exactly so, but very more to the point is whether we can maintain the
heat differential between hot and cold heads. Yes it'll be less
efficient if heat is lost in the displacer section - but that heat loss
will help to minimize boiling the working fluid.

We - you - can go round and round and round on this without getting
anywhere [DAMHIKT] so why not jump off the merry-go-round and live with
those losses for the first version? Once you have one working, then come
back to reduce losses.


Perhaps not as important as you think - it'll depend on your overall
design and operating parameters. There's a photo of a fluidyne with a
4-inch bore at the bottom of the web page at
http://www.iedu.com/DeSoto/Projects/Stirling/Dyne.html  - in which
Schedule 40 PVC pipe was used to build the displacer body. PVC works
reasonably well at low temperatures but turns to mush at temperatures
close to the boiling point of water.

Regrettably, to operate at decent efficiency, we need a large
temperature differential. If this is new to you, I think there's a
fairly good discussion of the Carnot cycle efficiency limitation in
Wikipedia - and you can find others with a Google search.

In order to sneak up on better Carnot efficiency, we need to use
materials that'll withstand higher temperatures than will phenolic or
PVC plastic. If you have time and money to burn, then ceramic materials
may be attractive - but my choice (because I'm just poor) is to go with
all-metal for the higher efficiency.


With a four-foot wide trough producing temperatures in the neighborhood
of 725F, the Carnot limit is a bit above 50% efficiency. My goal is to
push beyond 25% - and I'm fairly sure (approaching certainty) that I can
do that. I'd really like to encourage you to raise your sights...


I don't think so. They've both graduated and gone on with their lives.
If you're interested, you can do a Google search on their names and
follow up. I did, but didn't.


I worried about that for a time then took a different tack - I
reconfigured to minimize the amount of fluid in the engine. IOW, I
designed to minimize the effects of resonance/non-resonance in the
displacer. In a nutshell, I decided that it was much more important to
move energy from the hot head to the cold head (via
expanding/contracting working gas) than it was to push-pull water mass
back and forth in the displacer - with or without gravity assist.


Let me answer the 'what have you tried?' question by pointing you at a
pair of drawings showing a low-temperature engine and a high-temperature
engine at: http://www.iedu.com/DeSoto/Projects/Stirling/fluidyne.html  -
the engines shown have already been changed, but the these'll give you a
nother glimpse of designs that seem to work.


Ok. :-)

--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/

 Morris Dovey wrote:


I can't type/spell, too. The link should have been:

    http://www.iedu.com/DeSoto/Projects/Stirling/Fluidyne.html

Sorry for the bad link.

--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/