"Thermoacoustic" Stirling - theory of operation

[VincentG]

How, or in what way is the power "ruined"?

There is not much heat energy in a fixed volume of hot air, so between expansion and cooling from work output the pressure may reduce too fast. That's why I favor heat input for as long as possible. Even with my completely ideal 4:1 volume ratio isothermal model, the pressure is down to ambient at 55 degrees BBDC. How quickly would the pressure reach ambient without continuous heat input after compression? I think too early to make useful power.

It may work with a much larger starting hot space volume like a stock LTD(or similar), but these thermoacoustics(or similar) have much less gas to work with.

[VincentG]

100k KE = 1x
200k KE = ?
300k KE = ?
400k KE = 4x

Looks good to me, and looks like KE parallels another common value here.

...pressure. I was referring to how KE in gas doesn't "stack" like we'd like. IOW, double the volume and amount of gas, but we still get the same pressure. So to me there are two roads, keep making the engine bigger, or change the way we utilize the gas.

[matt brown]

In trying to find something on what Matt may be talking about I came across references to "the root mean square speed (velocity)".

But that applies, apparently to a given axis (direction of motion)

The STP speed of 'air' molecules is the speed of sound, so average values equalize quickly without local energy differences (local heat). Boltzmann spent years working out how heat moves thru gas, but his real challenge was whether shape effects distribution: simply consider 2x volume change in 2 dimensions (like piston in cylinder) vs 2x volume change in 3 dimensions. We know from various empirical tests how volume changes effect pressure changes, but proving this via molecular speed variations and collision ratios is a daunting task.

[Tom Booth]

How, or in what way is the power "ruined"?

There is not much heat energy in a fixed volume of hot air, so between expansion and cooling from work output the pressure may reduce too fast. That's why I favor heat input for as long as possible. Even with my completely ideal 4:1 volume ratio isothermal model, the pressure is down to ambient at 55 degrees BBDC. How quickly would the pressure reach ambient without continuous heat input after compression? I think too early to make useful power.

It may work with a much larger starting hot space volume like a stock LTD(or similar), but these thermoacoustics(or similar) have much less gas to work with.

Don't know. "There is not much heat energy in a fixed volume of hot air"

I don't think that is necessarily true or particularly relevant.

I can say there is not much gasoline in gas tank.

What I'm talking about is fully utilizing what's available. The engine volume, bore, stroke etc needs to be compatible with whatever "full utilization" actually turns out to be so you don't "run out of gas" before the next "fill-up". But depending on the application. OK so you need a bigger gas tank or something.

I don't have anything against "isothermal" expansion at the begining of the power stroke. It's probably inevitable anyway, and necessary to compensate for an increasing load but my schtick is just that the whole concept that a very LARGE percentage of heat MUST be discarded as WASTE heat to a sink, as a matter of "the laws of physics" is utter poppycock.

And such a theory cannot be supported by any experimental evidence or proof.

By what experiment was Efficiency = 1 - Tc/Th ever verified? Who did such an experiment? When, where, how?

Nobody, ever.

Period.

I've asked on a dozen science/physics/thermo forums for any such historical account of any experiment that verifies Efficiency = 1 - Tc/Th.

No one can cite any such thing. It doesn't exist.

[matt brown]

There is not much heat energy in a fixed volume of hot air...

This really is the basic problem that everyone seems to overlook and why I like this example:

(eng A) 100cc expanding to 200cc at 600k has the same output as (eng B) 200cc expanding to 400cc at 300k. Everyone is sweating bullets to achieve A when B has the same output and no fuel cost. Every time I peck this out, I have to wonder...

so between expansion and cooling from work output the pressure may reduce too fast. That's why I favor heat input for as long as possible. Even with my completely ideal 4:1 volume ratio isothermal model, the pressure is down to ambient at 55 degrees BBDC. How quickly would the pressure reach ambient without continuous heat input after compression? I think too early to make useful power.

Here's a walk on the wild side...

https://www.youtube.com/watch?v=gwtZkHoVMso

[matt brown]

By what experiment was Efficiency = 1 - Tc/Th ever verified? Who did such an experiment? When, where, how?

Nobody, ever.

Period.

I've asked on a dozen science/physics/thermo forums for any such historical account of any experiment that verifies Efficiency = 1 - Tc/Th.

No one can cite any such thing. It doesn't exist.

As I've said before, this is a mathematical reduction from some calculus, but this can be derived thru various means. It's just the ratio of expansion to compression work or eff = 1 - Wneg/Wpos expressed via two temperatures. Why you continue to dream that compression work supplied by ambient pressure doesn't 'tax' the cycle demonstrates various misunderstandings.

Most science forums see this as self-evident due to math proof and have a low pain threshold for anyone lost in the weeds. It's akin they use Arabic numerals while you use Roman numerals.

[Tom Booth]

By what experiment was Efficiency = 1 - Tc/Th ever verified? Who did such an experiment? When, where, how?

Nobody, ever.

Period.

I've asked on a dozen science/physics/thermo forums for any such historical account of any experiment that verifies Efficiency = 1 - Tc/Th.

No one can cite any such thing. It doesn't exist.

As I've said before, this is a mathematical reduction from some calculus, but this can be derived thru various means. It's just the ratio of expansion to compression work or eff = 1 - Wneg/Wpos expressed via two temperatures. Why you continue to dream that compression work supplied by ambient pressure doesn't 'tax' the cycle demonstrates various misunderstandings.

Most science forums see this as self-evident due to math proof and have a low pain threshold for anyone lost in the weeds. It's akin they use Arabic numerals while you use Roman numerals.

Often I hear that an extraordinary claim requires extraordinary proof.

I would consider the claim that if I or anyone, by any means were to supply 1 million Jules of heat to a heat engine. ANY heat engine that ever existed or ever will exist, on average, 80% or 90% of that supplied heat, or about 850,000 out of every 1,000,000 Joules is useless "waste heat" and must be thrown away pretty "extraordinary".

I don't find some dubious "reduction from some calculus" that you have, as yet, been unable to cite afaik extraordinary proof, ordinary proof, mathematical, logical or any kind of proof or evidence whatsoever and certainly not historical.

We have the equivalence of work and heat discovered and verified by James Joules experiments which experiments are recorded, verifiable and repeatable by anyone.

Not so with this "Carnot efficiency limit" equation.

It's not " a mathematical reduction from some calculus".

It's nothing more than Carnot's silly water wheel heat engine fallacy that heat "falls" from TH down to TC which was later extrapolated as a fall part of the way down to 0K. The distance of this supposed "FALL" from TH down to TC is a percentage of the "FALL" from TH to 0K or 1 - Tc/Th

Lack of any historical basis in any kind of real science or empirical evidence of any kind whatsoever aside, it currently fails to stand up to any attempt at experimental validation of the most rudimentary sort.

Such a prodigious "flow" of "waste heat" as is supposed to be exiting any heat engine from its cold end is nowhere to be found, at least not in any Stirling type hot air engines.

[Jack]

I get where you're coming from, but I think cold sinks are used for a different reason.

I don't think it's mechanically possible to get every last bit of heat turned into energy or work. It gets easier the smaller you go though. But you run into the law of diminishing returns.
Cold sinks do waste fuel, but they allow a heavier or bigger engine to operate. It allows for bigger differences in temperature because that big machine can't get anything out of the "waste" heat. So the fluid needs to be cooled down to reduce the work input needed.

In theory you're correct that all heat can be taken out by allowing the fluid to expand to wherever, but that inherently ruins any kind of power we can get from it.

Can you explain that last paragraph?

I understand your point of view, I think, and I would even agree that IF an engine, of whatever size cannot,for whatever reason, utilize all the heat supplied to it, the excess might need to be removed one way or another for the engine to continue running, maybe. (Though I think there are probably better solutions that have not been explored due to the prevailing theory that "waste heat" is inevitable and discarding it is somehow beneficial to the "flow" of heat through the engine, that is considered to be what actually powers the engine)

But to revisit that last paragraph:

"In theory you're correct that all heat can be taken out by allowing the fluid to expand to wherever, but that inherently ruins any kind of power we can get from it."

In my mind the process of expansion during the power stroke IS the process of "getting the power out of" the gas as it expands.

So I don't understand how you figure that "inherently ruins any kind of power we can get from it".

To my way of thinking it ("allowing the fluid to expand to wherever") is akin to driving your car until the tank runs out of gas, wherever it happens to run out, as opposed to driving your car a little way down the road and then dumping 80% of the "waste gasoline" on the road and then refueling.

I'm just curious about the thought process that leads to the conclusion that: "all heat can be taken out by allowing the fluid to expand to wherever, but that inherently ruins any kind of power we can get from it"

How, or in what way is the power "ruined"?

I'm going to try to explain this in my layman's thinking process.
It's a mechanical problem. At least that's the way I'm looking at it.
You have to design your engine roughly targeting the amount of heat available. Your engine will only start running at a certain threshold, when there's enough heat difference to overcome friction. That friction is higher when we design for power, things will need to be bigger.
If you design for efficiency, using every degree of difference, your engine will be smaller and thus easier to move.
You mentioned earlier that someone melted your gamma engine. That's what happens when you put a high efficiency engine on too much heat. If you put a high power engine on little heat, the result will be less spectacular.

If you find a combination of high power and high efficiency in an engine you can really make some money.

[Tom Booth]

...
You mentioned earlier that someone melted your gamma engine. That's what happens when you put a high efficiency engine on too much heat. ...

If you find a combination of high power and high efficiency in an engine you can really make some money.

The little LTD engine melting is a material issue. Plastic and foam rubber can't take any real heat at all and most of these little engines are not designed to take more heat than supplied by a cup of coffee

They come with instructions not to use a flame:

Resize_20231214_020359_9996.jpg (136.54 KiB) Viewed 26351 times

But, swap out the plastic and foam rubber for glass and lightweight pumice stone and your good to go.

https://youtu.be/fockxmOGTBs?si=Px1WvjFd6lXPh85O

viewtopic.php?f=1&t=5528

[Jack]

Yeah maybe not the best example on my part.

[Jack]

But it doesn't take away that there are mechanical losses to efficiency when you design for power and losses to power when you design for efficiency.
There's an overlapping point depending on the goal of the engine, but you can't have both.

[Jack]

See if I can explain it better from this angle.
With a lower temperature difference the change happens slower. With a higher delta it goes faster.
So for an engine to capture both it should both be able to do that fast and increasingly slower until it basically slows down to a halt. If you're doing it faster you're actually putting in work to expand the fluid "artificially".

[Jack]

Well if I explain it like this it sounds like a piston movement haha. I'm giving up, my head is too twisted for this stuff.

[Tom Booth]

Well, I think I get the general drift of what you're saying.

You may be right, I don't know, but what's the proof?

You can't have both high power and high efficiency.

IMO, efficiency is the effective conversion of heat into mechanical power, so I would say that the two go hand in hand. Of course, I could be wrong.

[Jack]

The law of diminishing returns has something to do with this. I think because catching and using all of the heat would just take too long. And forcing it to expand takes work.

In a flash there I thought maybe that forced expansion could be used in stead of water cooling. Whether you're powering a pump or using that work to "overstretch" the fluid to cool it further. I wonder which would be more effective and efficient.