Non-Working Fluidyne
On the last energy-related post, I ended with:
I have what I think is a good, simple, cheap design but I have to build and tweak it to make it work and have pictures/video.
I hoped to post a working example engine within days. Instead I have a non-working one after weeks. Anyway, here’s what’s supposed to happen.
There’s water in the lower part of the portion on the left as well, to the same initial height as shown in the clear tube. Apply heat as shown and the water in the clear tube should start oscillating.
This is basically a Stirling engine where the displacer piston is water and the displacer and power piston relationship is maintained by tuned parameters rather than an explicit mechanical linkage.
The idea is that the sun would heat the heater portion and water is pumped up to a reservoir. The water can then be let down through a generator for electricity at any time, not just when the sun is out.
Before I started down this path a few months ago, I googled around to see if anyone else had been trying it. I found one other guy who seemed to be a few steps ahead of me already.
Unfortunately, my engine isn’t working. I had originally build a completely jury-rigged one out of copper and clear tubing and it worked to some extent. Then I build a large PVC one based on correct mathematics (somewhat simplified) and had no success. I fixed some problems and got the above, which still doesn’t work.
It has a leak somewhere which can’t help much, but I’m pretty sure the leak is slow so I don’t think it can be the main problem. The water level in the output column rises and sometimes it suddenly lowers and then rises again, but it never really oscillates.
Based on advice from Morris Dovey, I shortened the displacer portion by cutting as much of the vertical PVC sections out as I could. It immediately started oscillating.
Next step: Get it pumping in the right ΔT range.
Glad to see you got it working! Generally these things will oscillate at least slightly if you can just get build somewhere /close/ to a good design.
I’m about to try building a fluidyne in a much simpler configuration – Basically the entire engine is in-line to eliminate all elbow and t-fittings, with the cold head in line with and above the hot head, and the regenerator connecting the two. I have a sketch on the web page at
http://www.iedu.com/DeSoto/Projects/Stirling/InlineV1.html
My struggle to hold down development costs feels like a losing battle. To prototype the new in-line version I’ve just ordered up the tools shown on the web page at
http://www.iedu.com/DeSoto/Misc/PumpTools/
If this new engine works as well as I think it should, it’ll demonstrate that a fluidyne can be even more efficient without the tuning tube on which C.D. West focused so much attention.
I had it working briefly, but then I melted the PVC portion. :(
Your single piston version looks like magic. I await news of the miraculousness.
From your link:
So. The reason my PVC melted was that the heat pushed the dispacer-water down too low. In an email to me, you mentioned adding water after *sealing* to increase pressure. But I hadn’t thought of adding water after *heating*.
The biggest problem is knowing the water level in there. I’m a donkey caught between two bales of hay on solving that. Method 1 would be lowering the temperature (which it has to be eventually), but then the engine doesn’t work. Fix it? Method 2 would be to switch from PVC to metal throughout, but then the expense.
I haven’t been by here for a while. Are you still working on this?
Since PVC tends to turn to mush somewhere near 200°F, it’s important to have the ends of the copper tubes immersed in the water to protect the tops of the PVC tubes.
The single piston engine is different only in that the cold head is disconnected from the displacer tube and located directly above the hot head. I machined a regenerator and a friend has volunteered to braze it all together for me, so I should know in a week or so if it runs as expected (probably not – I expect to have to tinker with it at least a little).
Remember than when you lower the hot side temperature you’re also lowering the efficiency – and that if you lower the efficiency too far, oscillation will suffer.
It depends on what you mean by “working”. I’m still *intending* to work on it. But I haven’t done anything in a while. I’ve been discouraged by failures.
IIRC, the problem was with pumping. I can get oscillations going fairly well but if I put a couple check valves in the line then it just doesn’t pump.
Hmm – just remember that discouragement is a /choice/.
I’ve seen this problem elsewhere – most often with spring-loaded valves that required more power to open than the engine could provide. There are two ways to deal with this: coax more power from the engine and/or replace the check valves with others that require less power to open.
garden hose stops (“Gardena type”) can be tinkered with to become a very good and cheap non-return valve.
But i am wondering about the pressure (your pumping height) and not just the power. If the pressure is not heigh enough you won’t get any pumping going on
Yes, you are probably right about the pressure. Although there have been times when I’ve had the check valves out of the line that the oscillations have been very strong. But maybe not strong enough or frequent enough.
I’ve actually had an all-metal version since this post. I’m trying to get consistent oscillation and map out some of the parameters before I jump all the way into check valves.
Thanks for the tip on return valves, but I think “host stop” and “gardena” must be European things, because I can’t find a local reference. Maybe we have a different term for it in the US?
I’m not really clear how it works from the picture.