Stirlingengineforum.com

Ok, admittedly I may be about to make a fool of myself, but what the heck. Please offer corrections where needed.

Lets get some energy conversions out of the way first, as I'll be bouncing from metric to SAE a bit.

1 Joule = .74 Ft/Lbs - Now traditionally a Joule is not used to quantify a static force, but that's what the internet says the conversion is, and we will need to measure power as a static force for this example. Perhaps this is where this whole example falls apart, but from what I can gather, a Joule is a Joule is a Joule, whether it is applied as heat or force.

The heat capacity of air is 1.005 kJ/kg - For simplicity's sake I'll reduce that down to 1 Joule to raise 1 gram of air 1 degree C.

We are going to use a displacer housing that is internally 1 foot in diameter and 1 inch tall, with a displacer of nearly the same diameter and .5 inches tall, thus giving us an air volume of roughly 56 cubic inches.

The weight of the air in the housing is 1.2 grams.

The surface area of the displacer housing plate is roughly 38 square inches.

Lets just use the typical operating range of an LTD engine, so from 20 degrees C to 100 degrees C or an 80 degree increase.

1.2 grams(weight of air in housing) x 80(delta T) = 96 Joules to raise the volume of air to 100 C.

We have gained 4psi of pressure within the housing that has a surface area of 38 square inches. This gives us a force of 152 Lbs.

Recall 1 Joule = .74Ft/Lbs

Cross multiply and this gives us a static force of roughly 205 Joules, all while inputting only 96 Joules to heat the internal volume of air.

Note that we could have shrunk the displacer housing height by half, and in turn would have halved input heat required for the same output.

Also note that this is only taking pressure gain into account, with no consideration to the energy gained from the kinetic energy that may(or may not) be available to us in the form of molecular energy. That is a challenge for another day.

When I saw this, I knew I'd need a cup of my best Jo before a second read...

It's never a good idea to mix 'stuff' and you have a witches brew near boiling. It's not just metric vs SAE which is obvious, but the obscure confusion of static vs dynamic values. Work is a summed total vs force is like a lady in waiting. The old ICE standard for work is PLAN/33,000=HP where P=mean effective pressure in psi, L=stroke in feet, A=area of piston in inches, N=number of pistons. Heck, if your piston was 2 ft in diameter, you'd have 4x the force, but still no 'work' until piston moves.

Nevertheless, I know exactly where you're going, gaming mechanical work vs PV work. Most guys think of heat engines as a device where mechanical work is a consequence of PV work, but you're looking at this mechanical work as a coincidence of PV work. This parallels uncoupling a normally considered coupled event, let's say strolling across a freeway at a given time and space (location) which is known to be fatal. However, if we choose a different time or space, no problem rolling across.

It's never a good idea to mix 'stuff'

Right you are Matt, though I have not mixed metric and SAE within an equation, so I would argue that if there is a discrepancy, then with who does the fault lay?

Heck, if your piston was 2 ft in diameter, you'd have 4x the force, but still no 'work' until piston moves.

Right again. In this case I am using static force in part because my math skills are not high level enough to equate this in a dynamic situation, and in part because I'm not so sure this isn't a dynamic situation anyway.

The force attained is really a snapshot in time of energy contained within a system. If we freeze frame at the moment a baseball bat strikes an incoming ball, there is no "work" done in the conventional sense, just a transfer of energy.

So If we are able to use the force within this system at a high cyclic rate, with no "movement" necessarily, what we really have is vibration, which is the fundamental form of energy anyway.

This parallels uncoupling a normally considered coupled event, let's say strolling across a freeway at a given time and space (location) which is known to be fatal. However, if we choose a different time or space, no problem rolling across.

Well said.

It appears that as the ratio of surface area to volume goes up, more of the energy is available as pressure.

This gain may continue until the layers of air molecules become thin enough that the internal volume and as such available pressure gain approach zero.

At the sweet spot, perhaps we are directly tapping into the "kinetic molecular energy" of the gas, or at least as much as this type of system will allow.

The more layers of air(and the more volume), the more energy is caught up in the "molecular chaos" that Boltzmann described heat as, and as such is less available to us as observed pressure.

Here is the paper as published by Nature magazine:

https://www.msn.com/en-in/news/techands ... r-AA1jgXhL

What is conveniently left out of the article is the input power and output power.

My assumption: The input power from the output power of the laser, ignoring the "noise power" from the signal generator, is maybe 1 to 6 watts, from the laser-head specification. The input power to the laser is 50 to 120 watts.

Output power of the engine particle, unknown. If it's in the paper it is lost to me in the jargon used. Total power output by the whole system appears to be zero.

Total efficiency: power out / power in = zero/50 = zero
Also: zero/1 = zero

Not 0.95 as hinted at. My take is they are still a very long way from getting any useable work or electricity from this micro-engine. And, a very long way away from disproving the second law of thermodynamics. The Carnot equation allows for efficiencies of 0.95 and higher, depending on T-hot and T-cold. Plus I think they've miscalculated and failed to account for real things.

They also point out in their paper:

Nevertheless, whether such interactions can be realized in experiments remains to be seen.

It seems to still be theoretical. My skeptic meter is pinging. A result of "extraordinary claims require extraordinary evidence".

The micrometer-sized Stirling engine was realized using cross-linked poly(styrene/di-vinyl benzene) (P[S/DVB]) colloidal particles of 5 μm, which were obtained from Bangslabs, USA. The harmonic potential used to trap these particles was generated by focusing an IR laser beam of wavelength 1064 nm with a 100X Carl Zeiss objective (1.4 N.A.) mounted on a Carl Zeiss Axiovert microscope. The laser beam was generated by a Spectra Physics NdYVO4 laser head. The particles were suspended in deionized water at extremely low concentrations of a few particles per microliter. The trapped particle was imaged using a Basler Ace 180 kc color camera at a frame rate of 500 frame s−1 for cycles with τ > 300 ms. To generate sufficient statistics at low τ, τ = 100 ms, 50 ms, 24 ms were imaged at 1000 frame s−1, τ = 20 ms at 1200 frame s−1, τ = 18 ms at 1333 frame s−1, τ = 16 ms at 1500 frame s−1, τ = 15 ms at 1600 frame s−1 and τ = 12 ms at 2000 frame s−1. The particle was tracked from the resulting images to sub-pixel resolution using custom made Matlab codes to an accuracy of 10 nm. WC and η were calculated from the particle positions using the framework of stochastic thermodynamics

Thanks for reading through this, it's definitely way out of my wheelhouse, and even as research papers go, is exceptionally hard to follow.

Admittedly, I've only skimmed through the paper, but it seems to me they observed the results, or at least think they have. That said, I think factoring in the input power of the laser is like factoring in the energy required to refine a gallon of gasoline.

The takeaway for me is the irony of the whole thing. If this was posted in Tom's physics forum, would it get locked out as claims of pseudoscience?

This type of mumbo-jumbo reminds me of the classic 'speed' question:

If you drive 30mph for 1/2 mile, how fast do you have to drive for another 1/2 mile to average 60mph for 1 mile total ??? Most guys simply say 90mph then a nerd points out that 30mph is 1 mile every 2 minutes and 1/2 mile at 30 mph requires 1 minute. And since 60mph across 1 mile requires 1 minute, you're 60mph 'time' (1 minute) is up at 1/2 mile at 30mph, so nerd says second 1/2 mile speed is infinite...

A hotter molecule (gas or whatever) might have more energy than a cooler one, but utilizing this 'greater' energy remains the challenge. Until ~1800, our non bio energy was limited to wind and water, but even here there's various misconceptions.

Take a waterwheel in a flowing stream...you can't abstract much energy from flowing water with an undershot waterwheel, since abstracting this energy requires a slower flow rate downstream. The typical solution is an overshot waterwheel where the upstream and down stream rates coincide, and the 'magic' is the head drop. Although both are waterwheels, and fairly similar in appearance, these are drastically different schemes.

However, a windmill is more technical. At first glance this appears a simple reaction scheme similar an undershot waterwheel, but like the undershot waterwheel, what happens to the 'wind' as it passes thru the windmill ??? There's no short answer, but this explains why we had dams dotting the landscape for many decades before windmills.

As for thermodynamics, the weird part is that the gas molecules are always in motion (except 0k) and don't lie on the ground like a bunch of micro marbles. You can't simply heat them and squirt them in a particular direction as a controlled force doing some type of work, then reheat them again to do more work.

The pesky nerd added a time constraint that the original problem did not impose eh? Good thing revenge of the nerds was just a show. *I said in 2023, fully aware of the impending AI revolution.

Missed your the latest post Matt. Just thought it was interesting stuff being tried by the real guys in lab coats. It's motivating to me that work is still being done to try and break the laws of physics, however fruitless it may or not be.

A rapidly varying electric field was applied to this micro-engine to switch it between two states, resulting in nearly 95 percent of the efficiency limit proposed by Carnot, which is the absolute maximum theoretical efficiency for any heat engine.

That seems a rather meaningless statement, since the Carnot limit is based on and varies with the ∆T.

That is, a coffee cup Stirling engine (running on boiling water in a 75°F ambient environment), with 20% efficiency is operating at 100% Carnot efficiency.

I don't disagree with you Tom.

matt brown wrote: ↑Sun Nov 12, 2023 5:01 pm A hotter molecule (gas or whatever) might have more energy than a cooler one, ...

.... the gas molecules are always in motion (except 0k) and don't lie on the ground like a bunch of micro marbles. You can't simply heat them and squirt them in a particular direction as a controlled force doing some type of work, then reheat them again to do more work.

Umm...

Why not?

I mean, if you have a sealed container with a moveable wall (piston), regardless of the initial rate of motion there is equilibrium, that is the SAME rate of motion on both sides of the wall that effectively cancel.

If you heat the molecules of gas inside the container the moveable wall will be driven out until the added heat/energy is exhausted.

Why could such a process of heating and expansion not be repeated again and again, indefinitely?