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Insulating the cold side
Posted: Thu Aug 15, 2024 9:38 am
by VincentG
I've converted this ringbom to run upside down with a bash valve arrangement impinging upon an enlarged closed cell foam displacer. This has produced impressive power from 1cc and a 180F hot side and 40F cold side. It runs stronger than my HTD model did with a torch.
It also has good torque at high rpm, something I never observe on these things. The magnets could not maintain timing advance at high rpm, and would over advance at low rpm.
https://youtube.com/shorts/N_unRr-M5NA? ... iMRUjmGZDP
Watch the slow motion and you can see that displacer movement is nearly perfect. Combined with the hot piston arrangement and it's a real runner. It does run better with ice, but I have insulated the cold side for a short time and it continued to run well.
In a future test I will insulate the bolts from the cold plate and put a heavy foam block over the top and see what happens running and not.
Re: Insulating the cold side
Posted: Thu Aug 15, 2024 9:57 am
by VincentG
Watching the video again, the timing needs to advanced quite a bit, and with that I'd expect significantly more power and higher rpm.
But for testing the insulated cold side, 0 degrees advance is probably ideal. Easy enough to change back and forth anyway but food for thought.
Re: Insulating the cold side
Posted: Fri Aug 16, 2024 1:54 am
by Tom Booth
What is the heat source for the 180° hot side?
Is it that brownish looking cylinder thing the engine appears to be perched on?
Just curious, but what is "a short time" the cold side was insulated? And was that before or after having been chilled by the ice? I assume the ice was either not yet put on or had been removed.
That is kind of opposite to what goofy suggested at one time. That the power piston, due to expansion cooling, might be better situated on the cold side.
However, there is friction at the power piston. Which with your arrangement, gets "recycled". I think cooling from expansion is diffused throughout the chamber and also likely mostly nullified by heat of compression, so overall, heat from friction is probably the dominant factor. At least my thermal imaging shows a great deal of heat emanating from the PP, even when situated on the cold side.
Kind of similar to my "hot potato" bash valve design from long long ago I never got around to trying, but yours is in an LTD format rather than single cylinder thermal lag type design.
For a "cold side insulated" test, if you wanted to pursue that further, I'd be interested to see the results with a regenerator incorporated.
That might help to reduce heat passing up into the upper cold chamber.
I had two different engines using the sidewall type LTD regenerator showing apparent below ambient temperature on the cold side.
Very interesting!
That's what I like about you VincentG. Very imaginative "out of the box" thinking and design work. That's what we need for progress in Stirling engine development. Daring innovation. Break away from the "standard" methods and try something new and different stop repeating all the old mistakes.
Re: Insulating the cold side
Posted: Fri Aug 16, 2024 2:19 am
by Tom Booth
You wrote:
The magnets could not maintain timing advance at high rpm, and would over advance at low rpm.
I assume that was before converting it to a bash valve design, so the magnets were removed?
I'd also be interested in seeing a test of having an "exact" 90° advance. In your design, that would, I think, be where the bash valve rod contacts the displacer to begin lifting it when the power piston is at its highest velocity, 1/2 way going up the cylinder.
The theory being that the momentum of the piston at maximum velocity combines with the "elastic" expansion of the gas, (or attempted expansion pressure buildup)
In other words, the piston is compressing the gas very hard at that point moving at highest velocity. Adding heat at that point (the driver) causes a delay in expansion, infact the gas is compressed as it is trying to expand.
The opposing forces, rather than resulting in a loss of power, the result is a very great build up of heat and pressure by the time the piston reaches TDC. The opposed forces, rather than canceling out, combine to produce a very high torque power stroke.
Not trying to "take over" your experiments, just something I think might be worth trying
How difficult is it, or what is involved in adjusting the timing? Do you change the length of the bash valve poker thing?
Re: Insulating the cold side
Posted: Fri Aug 16, 2024 2:34 am
by Tom Booth
I'm wondering what would happen if you eliminate the bash valve rod.
Maybe extend the throw of the piston for higher compression until the build up of pressure in the power cylinder alone results in the displacer being lifted.
In other words, the high pressure in the power cylinder lifts the displacer opening the "valve". It would probably work, but might take a lot of playing around with power cylinder volume, compression ratio and weight of the displacer.
An interesting possibility might be a screw type bash rod that can be adjusted on the fly while the engine is in operation.
I'm thinking ahead to a very large engine with a remote control timing adjustment built in in some way so it is not necessary to take the whole engine apart for a minor timing change.
Re: Insulating the cold side
Posted: Fri Aug 16, 2024 2:42 am
by Tom Booth
VincentG wrote: ↑Thu Aug 15, 2024 9:38 am
...
In a future test I will insulate the bolts from the cold plate and put a heavy foam block over the top and see what happens running and not.
Do you mean while the engine is being heated?
So,... While heating the engine, do a test with the engine running and not running?
That would be a twist.
Would you then measure how much heat is getting to the cold (unheated) upper side?
I'm afraid your foam displacer might melt in a heated but non-running engine.
Re: Insulating the cold side
Posted: Fri Aug 16, 2024 4:36 am
by Tom Booth
Is this where you got your engine:
https://www.ebay.com/itm/315419354273
I like the nice big thumbs screws. That should make disassembly and assembly easier.
Re: Insulating the cold side
Posted: Fri Aug 16, 2024 6:00 am
by Fool
I can't stress this enough. How ever you run your experiments, ensure that the piston side is warmer than both the ambient and the flat plate side. If not the piston and cylinder may condense moisture and the viscosity of that moisture may slow or stop the piston. Furthermore, excellent demonstration. Thanks.
Re: Insulating the cold side
Posted: Fri Aug 16, 2024 9:01 am
by VincentG
Thats the one Tom. It's a nice little engine but the open cell displacer is useless for much over a 30f delta.
Fool, I can confirm a cold glass cylinder quickly condenses water and the piston will seize. These glass pistons and cylinders have incredibly high friction with water.
Re: Insulating the cold side
Posted: Fri Aug 16, 2024 3:50 pm
by VincentG
I've done a bit of chamber testing on this engine(with a syringe for measuring) and despite having the same displacement as my epoxy test chamber, it has less than half the performance.
And my epoxy engine leaks quite a bit through the displacer guide rod while this ringbom is sealed tight.
On ice and room temperature my epoxy engine expands 1cc or more. This engine's chamber only expands .5cc or less for the same conditions, and would not exceed 1cc unless I got the bottom plate hot to the touch, and even then just barely, where my epoxy engine is 2cc+ at that point.
Disappointing to say the least, but very promising at the same time.
I might try and set up my epoxy engine as a ringbom or bash valve and use it for testing.
In any event, this new engine has a 1cc power piston and 16cc displacer piston after mods. I'd think the power piston needs to be bigger to get a proper heat pump effect no?
Re: Insulating the cold side
Posted: Fri Aug 16, 2024 4:28 pm
by Tom Booth
VincentG wrote: ↑Fri Aug 16, 2024 3:50 pm
...this new engine has a 1cc power piston and 16cc displacer piston ...
How do you get those figures?
That displacer looks like it nearly fills the entire volume and barely has room to move up and down, what looks like a few millimeters.
I'd guess there might be less than half that in actual gas volume. (Subtracting the volume taken up by the displacer itself).
Re: Insulating the cold side
Posted: Fri Aug 16, 2024 5:05 pm
by VincentG
Ok more accurately this chamber has 16cc of gas and the displacer moves 11cc. Thats a 2.6" displacer with a stroke of .13 inches.
My epoxy engine has 15cc of gas and the displacer moves 14cc.
Re: Insulating the cold side
Posted: Tue Aug 20, 2024 5:02 am
by VincentG
Tom Booth wrote: ↑Fri Aug 16, 2024 1:54 am
What is the heat source for the 180° hot side?
the engine was heated with a lighter
Is it that brownish looking cylinder thing the engine appears to be perched on?
A copper bar serving as a stand and hot sink
Just curious, but what is "a short time" the cold side was insulated? And was that before or after having been chilled by the ice? I assume the ice was either not yet put on or had been removed.
The ice was removed and insulation was placed on top. After a few minutes the top plate was 100F but still running well
That is kind of opposite to what goofy suggested at one time. That the power piston, due to expansion cooling, might be better situated on the cold side.
However, there is friction at the power piston. Which with your arrangement, gets "recycled". I think cooling from expansion is diffused throughout the chamber and also likely mostly nullified by heat of compression, so overall, heat from friction is probably the dominant factor. At least my thermal imaging shows a great deal of heat emanating from the PP, even when situated on the cold side.
i agree, a cold side piston is needed to test this properly but currently its so humid that a cold piston condenses water and quickly comes to a hault
Kind of similar to my "hot potato" bash valve design from long long ago I never got around to trying, but yours is in an LTD format rather than single cylinder thermal lag type design.
yes, it's a promising design and one that even Matt got behind, maybe I'll give it a go
For a "cold side insulated" test, if you wanted to pursue that further, I'd be interested to see the results with a regenerator incorporated.
That might help to reduce heat passing up into the upper cold chamber.
I had two different engines using the sidewall type LTD regenerator showing apparent below ambient temperature on the cold side.
Very interesting!
That's what I like about you VincentG. Very imaginative "out of the box" thinking and design work. That's what we need for progress in Stirling engine development. Daring innovation. Break away from the "standard" methods and try something new and different stop repeating all the old mistakes.
thanks, I agree we need to try somethingdifferent, not just build another st05
Re: Insulating the cold side
Posted: Wed Aug 21, 2024 8:26 am
by Tom Booth
I see the evolution going more or less along the lines of what this guy is doing, or planning on doing, with Peltier chips.
Starting, perhaps, with a small portable camp fire generator that could, at a minimum, charge a cell phone.
Re: Insulating the cold side
Posted: Wed Aug 21, 2024 11:37 am
by Tom Booth
Forgot the link:
https://youtu.be/x9a2rB-xWkY
IMO those chips are just too damage prone.
A friend of mine had a whole collection of old Peltier device stove fans that got overheated.
She liked them, and found it indispensable but overheated or just quit working sooner or later.