Model LTD max power effort

[MikeB]

I guess it's all theoretical to a degree, but if going with kinetic theory then each gas atom or molecule is moving independently with a lot of space in between hardly interacting with each other at all. If that is true than the idea that some of the hot gas can exert "pressure" to the colder gas is mythology. The hot gas molecule has to collide with a cold molecule which then collides with the next etc. until finally the last cold molecule next to the piston receives a final weak, diluted bump which knocks it into the piston.

Isn't that where the (actual) speed of sound comes into it? Pressure cannot propagate faster than that, so doing single-state analysis is going to be flawed at very high engine speeds.

Note that what I mean by actual speed of sound is to acknowledge that the velocity widely known as "Mach 1" is may be higher or lower depending on both density and pressure, which is not just different to "standard" in a Stirling, but also time-variant.

[VincentG]

Hmm the only mechanical influence here would be the gas velocity moving through the displacer ports that could potentially reach that speed.

But with a highly effective chamber, could the gas change temperature fast enough to change molecular speed by a localized mach number? If that makes any sense?

[Tom Booth]

Hmm the only mechanical influence here would be the gas velocity moving through the displacer ports that could potentially reach that speed.

But with a highly effective chamber, could the gas change temperature fast enough to change molecular speed by a localized mach number? If that makes any sense?

If Bumpkin is right and we should be looking more at the possibility of infrared (radiant) heat propagation, the propagation could, in theory, be the speed of light.

Perhaps not an entirely excluded possibility.

I've been reading/seeing more and more, information popping up regarding a form of near light speed ? (Or maybe it was sound speed) heat transmission (through solid materials) based on something, the name of which I can't remember now but basically a kind of "heat particle" like a photon. (Called a "phonon" I think)

Some "quantum" property, so not dependent on any mechanics of the engine. It wasn't clear to me under what circumstances this might be relevant, if at all, for our heat engines.

[Bumpkin]

To be clear, I've never proposed that radiant transfer has any effect on clear air; in. fact the opposite. I've only said that I think radiant heating of a heater, and radiant cooling of a cooler, that would then conduct heat to/from the working fluid, could be very significant. Apologies for any misunderstandings.

Bumpkin

[Tom Booth]

To be clear, I've never proposed that radiant transfer has any effect on clear air; in. fact the opposite. I've only said that I think radiant heating of a heater, and radiant cooling of a cooler, that would then conduct heat to/from the working fluid, could be very significant. Apologies for any misunderstandings.

Bumpkin

Do you mean, like heating the engine from the outside with a heat lamp?

Well, OK.

Regardless, the "weird' behavior observed by VincentG and myself where the power piston motion seems to mirror the displacer motion still looks to me like some form of internal radiant or other unusual mode of heat transmission. VincentG has given a different explanation.

Anyway, my apologies for the misunderstanding Bumpkin. I guess I have to take the credit for the revolutionary discovery, (or wacky idea) myself.

LOL.

[Fool]

Just an FYI: A phonon is a "photon" of sound. From phone meaning sound or voice, and quantum mechanical wave particle duality.

https://en.m.wikipedia.org/wiki/Phonon# ... to%20sound.

Heat is transferred at the speed of light by the infrared photon.

It's already been mentioned by someone that not all gasses absorb infrared. Oxygen and nitrogen don't. CO2 does. Water vapor better yet.

Heat transfers by convection and conduction. Convection is similar to conduction in that a fluid travels by a surface to conduct heat into the fluid body as it all moves by. The two types of convection are forced and natural. Natural depends on density differences and gravity. It seems more likely that most of the heat addition into an engine would be from forced convection. The displacer moves a little opening up a small gap where gas flows in very close to the hot surface, were it heats rapidly.

Speed of temperature rise in the gas depends on the thickness of the gas layer, and flow, and mixing. Turbulence can add to heating speed but it also increases wind resistance. Bigger heat exchanger surface areas, give thinner layers, but more resistance. Compromises needed.

It seems that the piston moves out proportionally to the displacer because the total air is heated proportionally. Lift the displacer half way. Half the air is heated half is cold. It gives half the volume increase, at constant pressure.

3/4 lift, 3/4's of the air is heated, gives 3/4 piston travel. It seems instantaneous because a small amount of air is hitting a large hot plate with a thin air layer to heat and forced turbulent convection.

If the piston is unattached and free to travel, the pressure will be fairly constant and about one atmosphere. This is called constant pressure expansion. Also called volume change.

[Tom Booth]

Just an FYI: A phonon is a "photon" of sound. From phone meaning sound or voice, and quantum mechanical wave particle duality.

https://en.m.wikipedia.org/wiki/Phonon# ... to%20sound.

Heat is transferred at the speed of light by the infrared photon.

...

Well yes, but the term is applied to heat as well.

In the same Wikipedia reference further down in the article, just for example:

...heat can flow via phonons that "tunnel" between two materials.[16] This type of heat transfer works between distances too large for conduction to occur but too small for radiation to occur and therefore cannot be explained by classical heat transfer models

[Fool]

Good pickup. I should have read the article fully.

[matt brown]

Vincent, I came across this recently when checking hot PP gamma

https://www.e3s-conferences.org/article ... _04002.pdf

a short read on dwell scheme with oval drive gears, but something else caught my eye that I had missed previously (on my HD prior my gamma deep dive)

hot PP gamma.png (71.04 KiB) Viewed 7609 times

[VincentG]

What caught your eye Matt? I've missed it.

[matt brown]

If this was LTD model, then PP would be on hot plate. I've found various studies on "hot end" gammas like this (fig. b)

hot vs cold.jpg (161.98 KiB) Viewed 7553 times

Everything else equal (always a risky premise) hot end displacer connection has same efficiency as cold end displacer connection, but a lot more output...

[VincentG]

Matt are those transfer ports drawn to scale? lol. I tend to think they are closer to ideal than we might think.

[Tom Booth]

If this was LTD model, then PP would be on hot plate. I've found various studies on "hot end" gammas like this (fig. b)


hot vs cold.jpg


Everything else equal (always a risky premise) hot end displacer connection has same efficiency as cold end displacer connection, but a lot more output...

Could you say where that image is from, and/or what you mean by "efficiency" in that context.

I'm trying to get some context for your statement:

"Same efficiency.... but a lot more power"

Does the actual heat input change?

Or in what sense, or in what way can you have "a lot more power" but "everything else equal" yet the same efficiency?

[matt brown]

Matt are those transfer ports drawn to scale? lol. I tend to think they are closer to ideal than we might think.

No doubt ideal, but paper in link has pic of test rig.

[matt brown]

If this was LTD model, then PP would be on hot plate. I've found various studies on "hot end" gammas like this (fig. b)


hot vs cold.jpg


Everything else equal (always a risky premise) hot end displacer connection has same efficiency as cold end displacer connection, but a lot more output...

Could you say where that image is from, and/or what you mean by "efficiency" in that context.

I'm trying to get some context for your statement:

"Same efficiency.... but a lot more power"

Does the actual heat input change?

Or in what sense, or in what way can you have "a lot more power" but "everything else equal" yet the same efficiency?

Tom, previous post in this thread with colorful screenshot has link above which is a short read on guy attempting dwell via oval gears.

The later black & white screenshot is from another short read

https://www.sciencedirect.com/science/a ... ge&fr=RR-1