Looking for fluid piston stirling engine math

That's interesting. Do you understand why it works? What appears to be critical?

So far as equations go, you'll need some sort of heat transfer into the brass and then into the water, some description for how the head changes in the left hand section, and then the resistance to flow in the rest of the system.

However I am stuffed if I can see whether that will capture the harmonic motion.

Cheers

Greg Locock

| On Wed, 23 Aug 2006 17:30:32 -0500, Morris Dovey wrote: | || I've come up with what one of the guys on news:alt.solar.thermal || tells me is a fluid piston stirling cycle engine; and have put || what I know so far (with drawings) on the web page at the link || below. || || Can anyone provide (either with a link to web page(s) or directly) || the equations that would permit intentional design of a refined || version of what I've cobbled together? | | That's interesting. Do you understand why it works? What appears to | be critical?

Interesting, yes - understand? Not really. There doesn't seem to be much that could really be critical - though if I heat too much of the brass tube, then it doesn't seem to want to oscillate.

| So far as equations go, you'll need some sort of heat transfer into | the brass and then into the water, some description for how the | head changes in the left hand section, and then the resistance to | flow in the rest of the system.

Hmm - OK, I think I'll add this to my project "TBD" list for now. It's beginning to seem as if a trial and error approach will be more productive than an engineering approach. As a matter of fact, I /am/ feeling more and more like a monkey with a typewriter...

| However I am stuffed if I can see whether that will capture the | harmonic motion.

Me too - but I'm not going to let it stop me. I've decided to scale up from 1/2" plastic tubing to heavy-duty 4" PVC pipe - with heat supplied by a solar concentrator. If I can get that to oscillate, then I'll build the pair of check valves and see if I can get it to actually pump water.

-- Morris Dovey DeSoto Solar DeSoto, Iowa USA

You might be able to develop it more rapidly if you use an approach called Design of Experiments, or Taguchi.

That is, decide on what the important factors are, then test them in various combinations (a Designed Experiment). If this is done properly then you can extract the relationships between the factors in a meaningful way.

Cheers

Greg Locock

| You might be able to develop it more rapidly if you use an approach | called Design of Experiments, or Taguchi. | | That is, decide on what the important factors are, then test them in | various combinations (a Designed Experiment). If this is done | properly then you can extract the relationships between the factors | in a meaningful way.

I think you're right - I've been considering building a set of motors (2", 4", and 6" "hot" sides, and 2", 4", and 6" "cold" sides) and a set of pumps all connectable (is that a word?) with a common connector type. I think it'd be informative; but pre-supposes instrumentation I don't have. If the (all 4") version works as expected, then I'll see what I can afford to carry out the experimentation.

I once heard that in order to ask a good question, it's necessary to already know half of the answer. :-)

I'm _so_ new at this that I don't know what the important factors are - a good indication that I don't know even half of anything. %-P

I posted my original article to the groups I normally read (alt.solar.thermal, rec.woodworking, and alt.binaries.pictures.woodworking) and additional groups where I thought I might (and did) find help (alt.engineering, alt.sci, and sci.engr.mech) and got so many responses and suggestions that I'm having difficulty responding /and/ getting any work done - so I think I'll try to keep what I'm doing and plan/hope to do on my web site.

If there's interest here in sci.engr.mech, then I'll post a note whenever I think I've reached a milestone - and those interested can look it over on the web page. That way I'll be able to share drawings and photos as well as text.

Thanks for your excellent input!

-- Morris Dovey DeSoto Solar DeSoto, Iowa USA

This reminds me of a self steered solar collector made by an MIT student a few years ago from miscelaneous plumbing: copper pipe, elbows, etc..

The motive force was provided by propane which moved from one side pipe to the other depending on the solar heating which could hit the pipe past a sun screen. The frame was pivoted at the appropriate angle to track the Sun squarely as it crossed the sky. It would catch up after a cloudy interval, even. I wouldn't be surprised to find it still online.

Brian Whatcott Altus OK

| On Wed, 23 Aug 2006 17:30:32 -0500, "Morris Dovey" | wrote: | || I've come up with what one of the guys on news:alt.solar.thermal || tells me is a fluid piston stirling cycle engine; and have put || what I know so far (with drawings) on the web page at the link || below. || || Can anyone provide (either with a link to web page(s) or directly) || the equations that would permit intentional design of a refined || version of what I've cobbled together? | | | This reminds me of a self steered solar collector made by an MIT | student a few years ago from miscelaneous plumbing: copper pipe, | elbows, etc.. | | The motive force was provided by propane which moved from one side | pipe to the other depending on the solar heating which could hit the | pipe past a sun screen. The frame was pivoted at the appropriate | angle to track the Sun squarely as it crossed the sky. | It would catch up after a cloudy interval, even. | I wouldn't be surprised to find it still online.

Brian...

That sounds a lot like the zomeworks.com tracker. They're still selling them.

-- Morris Dovey DeSoto Solar DeSoto, Iowa USA

I think Zomeworks started with this tracker around 1996. I fancy it was a development of the device in question. Propane pushes anti-freeze from side to side. Some variation of this approach must make a reasonable frame for solar cells. Pretty cheap, pretty reliable, pretty easy to make, I reckon.

But you wanted the analytical thermodynamics, didn't you?

Brian Whatcott Altus OK

| On Sat, 26 Aug 2006 21:48:26 -0500, "Morris Dovey" | wrote: | || That sounds a lot like the zomeworks.com tracker. They're still || selling them. | | I think Zomeworks started with this tracker around 1996.

I think Steve Baer published his tracker idea and started Zomeworks back in the 70's - but may not have taken it commercial until later. '96 sounds a bit recent, tho.

| I fancy it was a development of the device in question. | Propane pushes anti-freeze from side to side. | Some variation of this approach must make a reasonable | frame for solar cells. Pretty cheap, pretty reliable, pretty | easy to make, I reckon.

Probably. However, I'm going to try for 2-axis tracking using a pair of expansion chambers and a double-acting hydraulic cylinder for each axis. I'm going for a fairly fine focus on a relatively small-diameter pipe.

| But you wanted the analytical thermodynamics, didn't you?

Yes. It has been more than 40 years since I studied this stuff in school (and knew at the time that I'd never have any use for it) and the memories are fairly dim.

Actually, I'm not sure that this thing is readily modeled. It appears to operate simultaneously as a stirling cycle engine (expanding and contracting a volume of air, with fluid pistons) /and/ a steam engine (a relatively small - but apparently significant - amount of water is converted from liquid to vapor and back to liquid each cycle).

-- Morris Dovey DeSoto Solar DeSoto, Iowa USA