Constant volume compression/expansion-displacer chamber analysis-heat powered mechanical amplifier

[VincentG]

...this title could go on and on...

This video shows my ltd engine being spun without the power piston connected, operating on boiling water and ice. https://photos.app.goo.gl/17PjLX2A34X3s5AN8

We can view a pressure swing just as if the engine was running normally, only in this case we have constant volume compression and expansion. It does not much seem to matter how fast it is spun, the pressure swings are close to the same. This seems to tell me the displacer chamber is rather efficient in quickly changing the temperature of the gas.

I've demonstrated, at least to myself in this next video, that there is a constant flow of heat energy between the hot and cold sinks based on displacer position that we use to manipulate air pressure. https://photos.app.goo.gl/Xa9e8qaf5dHpkrb89

The best we can do is use interrupted and partial bites of this energy. When powering a piston this is easier said than done. However in this configuration I believe that the most efficient use of this energy will be found at the highest cycle rate in which there is still a full(or maybe nearly full) pressure swing.

Power out is much greater than power in(displacer movement). The major benefit here is the potential to heat and cool a huge volume of air without the need for a large piston and cylinder.

The hurdle is how to utilize this energy. I think the answer is in recovering the resonant energy via a very large vibration harvesting generator similar to a loudspeaker, or any number of methods described here. https://orbray.com/magazine_en/archives/1261

For me the key to this is unlike a free piston, we can directly control the cycle rate regardless of load. This should make it much easier to generate consistent power without the need for high end electronics.

Constant displacer motion could come from something as simple as a gravity powered counterweight driving the crankshaft, or a small electric motor.

What do you guys think?

[matt brown]

We can view a pressure swing just as if the engine was running normally, only in this case we have constant volume compression and expansion. It does not much seem to matter how fast it is spun, the pressure swings are close to the same. This seems to tell me the displacer chamber is rather efficient in quickly changing the temperature of the gas.

I've demonstrated, at least to myself in this next video, that there is a constant flow of heat energy between the hot and cold sinks based on displacer position that we use to manipulate air pressure.

The best we can do is use interrupted and partial bites of this energy. When powering a piston this is easier said than done. However in this configuration I believe that the most efficient use of this energy will be found at the highest cycle rate in which there is still a full(or maybe nearly full) pressure swing.

No such critters as constant volume compression and expansion, but I get what you're saying.

It looks like you're falling for a low tech Otto. I get your basic conclusions...that when low thermal ratio, nix regen and focus on other issues. Heck, when low thermal ratio, the theoretical cluck:buck ratio between various cycles narrow, as does input temperature issues. Your observation of pressure swing highlights just how fast temperature swing drives pressure swing. Overall, I suspect you're trying to have thermal & mech events coincide with a simplicity that provides more rpm to compensate less power per stroke. And all this schemed together where a low input source trumps a high input source.

This puts something like Tom's Hot Potato on the fence, but there's a very simple way to achieve your aims (if I have you correct). Once you lower input source EVERYTHING CHANGES and for simple Otto there's only one awesome choice, but it ain't obvious. I'll send it shortly...

[matt brown]

Ericsson Caloric.png (234.12 KiB) Viewed 9741 times

Oh yeah, here's one you'll recognize (I couldn't find mine on computer).

Looking at this Ericsson patent drawing, forget everything on the left side and entire furnace under engine. Focus on the right side, where upper cylinder A includes piston A, lower cylinder B includes piston B, and pistons A & B move in tandem. First, let's nix those valves in cylinder A head, and replace the conrod connecting piston A top with a conrod connecting piston B bottom (thru lower cylinder B). Next, let's consider those 2 vertical things (part 'D' ???) connecting pistons A & B are tubes, whereby gas can freely flow between cylinders A & B. Now, nix areas S & C in lower region of cylinder B and square bottom of cylinder B to coincide piston B.

Last, consider cylinder A area below piston A (currently) a heating region, and cylinder B area above piston B (currently) a cooling region (forget Ericsson). A simple scheme that can be open or closed cycle, can include a bounce gas chamber between cylinders, etc. Definitely not the most efficient or powerful scheme, just the simplest.

[VincentG]

Although I'm demonstrating at a low thermal ratio, I think this same cycle will work at far higher ratios than can normally be achieved while eliminating high temp lube burnout and friction issues.

I'm currently constructing a much more efficient and high temperature capable displacer chamber. Its intended for LTD development but hopefully it will be useful here as well.

[VincentG]

No such critters as constant volume compression and expansion

I don't know, there can be constant volume compression of a solid.

https://www.tekscan.com/blog/pressure-m ... sion-force

While there is no reduction in volume, the gas is acting to compress itself against the fixed structure of the displacer chamber. The same applies to expansion.

[Tom Booth]

No such critters as constant volume compression and expansion

I don't know, there can be constant volume compression of a solid.

https://www.tekscan.com/blog/pressure-m ... sion-force

While there is no reduction in volume, the gas is acting to compress itself against the fixed structure of the displacer chamber. The same applies to expansion.

The Rudolph Vuilleumier heat pump depends on constant volume heat induced compression and expansion of a gas.

https://patents.google.com/patent/US1275507

This somewhat also depends on the propensity for hot and cold air to coexist in a single volume of air without necessarily transferring heat between them.

In the patent there is this diagram to illustrate the principle:

Resize_20230604_165613_3301.jpg (31.43 KiB) Viewed 9721 times

Though divided into two compartments, the total "volume" of air is connected.

By heating and expanding the air in one chamber, the unheated cold air in the other chamber is compressed.

Likewise, lifting the displacer 1/2 way heats SOME of the air in the bottom of the LTD engine, the remaining cold air is compressed.

Actually the compressed cold air does increase in temperature due to the "heat of compression".

The opposite is also true. Cooling 1/2 the air will expand other portion lowering its temperature due to expansion

This heat induced expansion and compression is used to transfer heat but the total volume does not change.

Matt is correct if the two portions, heated and unheated are considered separate "volumes" but you are also correct since both volumes are actually contained within a larger volume which remains "constant".

[Tom Booth]

...this title could go on and on...

This video shows my ltd engine being spun without the power piston connected, operating on boiling water and ice. https://photos.app.goo.gl/17PjLX2A34X3s5AN8

We can view a pressure swing just as if the engine was running normally, only in this case we have constant volume compression and expansion. It does not much seem to matter how fast it is spun, the pressure swings are close to the same. This seems to tell me the displacer chamber is rather efficient in quickly changing the temperature of the gas.

I've demonstrated, at least to myself in this next video, that there is a constant flow of heat energy between the hot and cold sinks based on displacer position that we use to manipulate air pressure. https://photos.app.goo.gl/Xa9e8qaf5dHpkrb89

The best we can do is use interrupted and partial bites of this energy. When powering a piston this is easier said than done. However in this configuration I believe that the most efficient use of this energy will be found at the highest cycle rate in which there is still a full(or maybe nearly full) pressure swing.

Power out is much greater than power in(displacer movement). The major benefit here is the potential to heat and cool a huge volume of air without the need for a large piston and cylinder.

The hurdle is how to utilize this energy. I think the answer is in recovering the resonant energy via a very large vibration harvesting generator similar to a loudspeaker, or any number of methods described here. https://orbray.com/magazine_en/archives/1261

For me the key to this is unlike a free piston, we can directly control the cycle rate regardless of load. This should make it much easier to generate consistent power without the need for high end electronics.

Constant displacer motion could come from something as simple as a gravity powered counterweight driving the crankshaft, or a small electric motor.

What do you guys think?

Just for some clarification; mostly regarding the statements I've highlighted in blue.

First; "fast" is relative. So when you say "It does not much seem to matter how fast it is spun, the pressure swings are close to the same" you are comparing spinning it slowly by hand and spinning it "quickly" by hand.

I can agree with that. What puzzles (or puzzled) me is when an engine of one type or another is running at a speed so fast that the movement is a blur. Some engines are able to operate at close to 10,000 RPM

Your argument here seems to be that the RPM should be held down: " I believe that the most efficient use of this energy will be found at the highest cycle rate in which there is still a full(or maybe nearly full) pressure swing."

Regarding the second statement I've highlighted in blue about the constant flow of heat...

I don't disagree with your conclusion, in the case of your LTD engine, at a slow to moderate speed and with a metal ceiling (incidentally, chilled by ice).

I get the feeling your statement "I've demonstrated, at least to myself..." may have been made with regard to my opposing view, or Matt's thread "....no heat sink req'd"

Put the emphasis on required

I agree that under most ordinary circumstances heat transfer certainly does take place. What I've mostly been looking at is the outliers; the unusual engines running in unusual ways, at extremely high speeds, without a flywheel, with non-heat-conducting material on the "cold" side, or with the cold side insulated.

I agree, in most standard engines running at reasonable ordinary speeds, made of the standard materials heat transfer certainly does take place, and plenty of it. The engines are designed that way, with the idea of powering the engine by transferring heat through the engine.

This has been the way, the accepted standard for centuries. IMO however, little advancement has been made using that approach in the past 200 years.

Perhaps you are on to something and I'm quite sure some improvements are possible by twerking timing and dwell and whatnot,but if something as fundamental as the idea that "waste heat" is REQUIRED by LAW, due to the Carnot LIMITATION. If that assumed fundamental "law of the universe" is "NOT REQUIRED" then wow.

I've been told a half dozen times on the Science and Physics forums, (and in here a few times as well) that if I could prove THAT I'd get the Nobel prize and be rich and famous, usually just before my thread is locked and I'm banned from the forum. Those things are not my goal or my ambition and I certainly don't want to discourage your efforts in any way. Until proven conclusively, I may be on a wild goose chase. Any and every avenue for improving these engines that can be investigated should be investigated. Your approach of rapid prototyping to test new ideas has certainly led to some outstanding results

[matt brown]

...but if something as fundamental as the idea that "waste heat" is REQUIRED by LAW, due to the Carnot LIMITATION. If that assumed fundamental "law of the universe" is "NOT REQUIRED" then wow.

As I've often said, and I'll repeat, Carnot is chiseled in stone, BUT only for the common 4 process 'regular' cycles with opposing heat & cooling interleaved with opposing compression & expansion. The academics have this correct.

However, the Carnot buzz has been extended to all thermo cycles and this is wrong. In short, the academics have created a 'proof' where it's impossible to prove a negative. Well, I'll upset their apple cart, cause I have the proof. I recently stumbled across a cycle that needs no heat sink, but like a lot of thermo, this cycle requires certain volume vs thermal ratios. Nevertheless, many thermal ratio cycles are possible within these constraints and there's more than enough wiggle room to bridge the gap between ideal and real. And this bugger can be open or closed cycle.

So, I got lucky, really lucky, but I thought it was an anomaly at first. Then, while gaming various values (PVT stuff) a crude pattern emerged which was akin how it works, but not why it works. Once I discovered why this works, everything was...obvious, but it still took me a while to figure out the tiny equation that governs this 'magic' (couldn't resist).

This will likely change a lot of stuff, but science will adjust quickly, since the academics love their over paid mumbo-jumbo. They'll simply rewrite the wishy-washy 2nd law of thermo and add a few Carnot mods. It's kinda funny that I feel more huh than hoopla, it's not what I thought the elusive Holy Grail would look like...

[Tom Booth]

...They'll simply rewrite the wishy-washy 2nd law of thermo ...

And why not. With 2 dozen or more versions out there already...

More likely it would just be ignored or redefined like COP for heat pumps.

As far as :

As I've often said, and I'll repeat, Carnot is chiseled in stone, BUT only for the common 4 process 'regular' cycles with opposing heat & cooling interleaved with opposing compression & expansion. The academics have this correct.

However, the Carnot buzz has been extended to all thermo cycles and this is wrong

Referring to the so-called "efficiency equation" (or it's interpretation) that predicts any little Stirling engine or engine of any kind running on hot water with an ambient "sink" must, absolutely unload or "reject", (pass through) 80% of the heat supplied to it...

In my book if it's not true, it's not true and goes into the scrap bin of irrelevancy to be ignored, never again to be brought up in polite conversation. Four cycle, two, one five cycle, whatever, if it's wrong in principle it's wrong, and we just have to figure out why it ever looked right sometimes.

Remember, even a broken clock is still right twice a day. That doesn't mean we should ever rely on it.

It's conceptually invalid. The whole "flow through" "water wheel" concept of heat conversion it's based on is invalid.

"ENTROPY" can go right along with it. No such thing. A fairytale invented to shore up the Carnot mythology after the caloric theory went by the boards. Just another name for "waste heat" that hasn't yet been accounted for.

[Tom Booth]

BTW, I was searching "Nobel Prize" on this forum, to see where or when it was, or how many times...

Anyway I came across this thread. For some reason the patter of the OP reminded me of you Matt.

Also it shows how long this kind of theorizing has been going on in here. A little before my first arrival. (I think?)

viewtopic.php?f=1&t=847&hilit=Nobel+prize

Anyway, I haven't followed the link to the paper or whatever about this engine or heat pump or whatever it may be. Not sure the link still works, haven't had time to review the thread really, maybe later.

But as VincentG pointed out recently, so many years of theorizing has gotten nowhere. I'm not up for another 2nd Law / Carnot debate. I'm going to shut up for a while and try to focus on the Ringbom (modified) generator conversion.

[Tom Booth]

Well, the links are no good, but the URL was captured by the Wayback archive:

https://web.archive.org/web/20131024070 ... monotherme

Coincidentally?

This "monotherm" heat pump uses "constant volume" expansion and compression to create an "internal cold source" maintained by converting heat into work.

Another Teslaesque "cold hole" ambient heat engine.

I found the solar concentrator a rather interesting idea.

concentration_clip_image002.jpg (35.96 KiB) Viewed 9681 times

Two linear fresnel type mirror arrays focus the suns rays into a point using a fairly small footprint.

Some interesting "open source" research from this group.

[VincentG]

Tom to be clear I'm not taking a dig at your stance at all. In fact I'm also a proponent of expansive cooling. This is just a test of the other end of the spectrum to see the limits of a constant volume system.

I agree I have not yet cycled this very fast yet. I do plan on trying it out. I believe the cycle rate will only be limited by the material and efficiency of the heat exchanger design in conjunction with the way the displacer mixes the air. The goal is basically to achieve free piston/acoustic cycle rates in a controlled fashion. I think the displacer should lead the piston unlike the standard free piston model where the displacer lags behind.

[Tom Booth]

One other point that might be worth mentioning.

Your videos have the heat source on the bottom.

I used to completely discount the role played by the fact that hot air rises, however, as stated briefly before, experimenting with running LTD engines on ice, with the ice underneath, has caused me to appreciate that heat does not automatically flow from hot to cold in all situations and the fact that hot air rises does apparently play a role.

Consider the hot surface on the inside of the displacer chamber.

If heat is on the bottom, when the displacer lifts, the heated air molecules at the interface between the hot plate and the air rise by convection, making room for more air to move in to be heated.

In the opposite case with the hot plate on top the heated air at the interface "floats", that is, stays put, forming a kind of insulating layer rather than immediately rising and making room for more air to be heated.

I would have thought this "buoyancy" of hot air would be completely negligible and not effect the operation of the engine one iota, but after many experiments and repeated observations I think I can say with some confidence that without the natural convection resulting from having the heat on the bottom, the engine runs less cheerfully. There is some reluctance or sluggishness to the engine compared with when the heat source in underneath the engine.

It isn't just a matter of the heat from a flame rising to meet the engine but internally as well.

There has been a number of times when an engine, sitting on ice, would not start up at all, if the engine was in any kind of depression, surrounded by insulation, but no insulation on top.

Once running, the agitation from the displacer helps, but the internal buoyancy of the hotter air seems to really cause the engine to run more laboriously, like going up-hill.

Really, IMO the heat is not making any real effort to pass into and through the engine to get to the cold. The buoyancy of the hot air inside plays a role in just allowing heat to rise up into the engine at all.

[Tom Booth]

My point isn't that heat transfer does not or cannot take place, just that it seems to be a matter of local molecule collisions. There is no "outside force" compelling heat to flow from hot to cold.

Statistically, as a collision takes place between a hot and another hot molecules, the transfer is mutual so no net transfer takes place, but between hot and cold, some energy is transfered, so on a macro scale, the heat appears to flow in the general direction of the cold but this is not an "aggressive" compelling force, similar to gravitational force causing water to flow downhill, it's more of a passive tendency that at times hardly seems to exist at all.

Anyway, I'm heading over to the shop to work on that generator and don't have internet access there.

[VincentG]

Tom I do fundamentally disagree with that, but putting that aside...I think its strange to view dumping heat into the cold sink as a waste when the whole reason these engines run is through temperature differences.

The fact that we have unlimited ambient cooling should be taken advantage of to the fullest extent IMO. We are essentially given a free cold power stroke with no net work loss.

To me not taking advantage of this would be like not using hydro electric power from a dam. Or driving your car up a hill and then not coasting down.

The elusive "cold hole" is just an exaggerated version of what we already have with ground temperature or ambient cooling. Its far easier to make heat than cold, and as you have stated(correctly I believe) there is more power to be had from 300k to 600k than from 0k to 300k, for instance.