Stirlingengineforum.com

Doing some more testing, this time for volumetric expansion.

According to a combined gas law calculator, with a starting temperature of 40 degrees F and the 15cc capacity of the chamber, the final volume at 212 degrees F should be 20cc total. In testing I am getting right about 4cc (19cc total) which seems exceptional and a much better result than pressure testing would indicate. I've found the volume of my pressure testing rig is too high to get accurate results with pressure. But with volume expansion, extra "dead space" here does not have nearly as big of an impact. So I bet with a digital pressure transducer I would get better pressure results.

In fact, even with my excessively large 50cc glass syringe, I'm getting measurable expansion (just shy of 1ccc) between ice on the top plate and my 65 or so degree kitchen.

Still waiting on my smaller test cylinder, so I tried some new tests with the larger 50cc syringe. By taping a 1.5lb copper bar on the 1 square inch piston, I can apply 1.5psi to the displacer chamber. On just hot water and ice, you can see in the video the chamber is easily able to set the piston into oscillation. Even with a large amount of dead air in the syringe, it has no problem lifting the weight rapidly. I ran out of memory so it cut off the part showing that the chamber can barely lift the weight with a starting charge of just 1ATM.

I would estimate that if I used a heavier weight, it would lift it equally as well, as the heavier weight will simulate an even higher charge pressure.
If I try to move the weighted piston that quickly by hand, it's not easy at all and my wrist gets tired lol. Pretty impressive I think from only 15cc and a cup of hot water.

Although the weight is just used to simulate a higher charge and buffer pressure, this arrangement of setting a large mass into oscillation could prove very practical. I'll need to get a glass pressure vessel to test at higher pressures and with other types of gas using a normal free piston.

The arrangement of a driven displacer and a free power piston seems extremely effective and simple. Obviously a linear generator is needed to take full advantage of this, adding difficulty. But the benefit is constant mechanical effectiveness from the piston. That is, there is no connecting rod/crank angle issues to limit torque near TDC and BDC like in a normal engine.

https://youtube.com/shorts/WPtcVRK35nU? ... H3OG_zNEL4

Edit: It will even set the piston into pretty good oscillation with just ice on the top and room temperature as the heat source!

I've repeated the tests with a 4lb steel weight. The chamber was just as easily able to set it into oscillation, even on just ice and room temperature on the bottom plate.

It became clear to me that the only limit to this will likely be the heat transfer rate of the aluminum plate, and that just two ice cubes could set in motion a 100lb mass!

In fact, unless I botched the calcs, my .125" thick 2.5" diameter aluminum sinks can conduct 6600 watts at just a 30k temperature difference...someone please correct me if I botched that.

With a chamber pressure of 115psi absolute(result of 100lb weighted piston), only just above 3 joules is needed to heat air 30 degrees k.

This allows a practically unlimited weight capacity to this system.

I'm using online calculators mainly....surely I must be making a mistake somewhere!

I've done some expansion testing with a much smaller 10cc glass syringe. With ice on top and over boiling water, the expansion is 3.8cc, out of a possible 5cc assuming 40F(277k) and 212F(373k). The next step would be temperature sensors on the inside of the plates to see what the actual temperature reaching the gas is.

But this engine is just too small and I believe thermal performance will increase when scaled up. I've also realized the general shape and construction of these style pancake engines leaves a lot to be desired. But I'll save that for a future post.

For now I'll consider the input temperature, giving a temperature ratio of 1 to 1.25. The observed expansion ratio would give us a PP/DP volume ratio of 1 to 3.94.

So theoretically this 15cc chamber would be at the zero point with a 4cc power piston. That is again to imply that there would be no forced compression or expansion.

Based on what I observed in this thread, viewtopic.php?t=5638 that means this 15cc chamber could run quite well with a power piston of around 9cc. I may get around to trying this but for now my attention is on the 60l drum project.

A (very basis) control experiment for volumetric expansion was conducted.

I placed the 50cc syringe in the freezer for about 5 minutes. It was then set to 30cc and capped off.

Then I rotated it around the surface of boiling water and recorded the expansion. 39cc was the maximum I saw.

Using the ideal gas calculator and assuming a starting temperature of 30 degrees F and a final temperature of 210F, I should have seen an expansion to 41cc. 2cc short of the target.

The epoxy test engine is 15cc and under roughly the same conditions was about 1.2cc short of the target.

The test engine is expanding air into a room temperature cylinder, so expansion is lost in that regard. That and the Tc of the engine with just ice on top was likely above the Tc of the syringe after being in the freezer.

I would like to set up a more accurate test to see just how "ideal" a test rig has to be to duplicate the predicted expansion rate exactly.

The conclusion for now is that it's relatively easy to build a chamber with essentially ideal real-world performance. So once this level of expansion is reached, effort is better directed to other issues.

Response time of the chamber is likely the next question of interest.

Some quick and dirty response time testing until I get some kind of rapid response pressure transducer. The 10cc syringe is very light and so I don't think its inertia is impacting results much. The temperature difference here is very low. The water below the engine was cooler than the top plate due to the house heating up during the day and the water temp lagging the air temp.

I was unable to measure the driven rpm but I would estimate around 2k rpm. You can see the piston is only slightly lagging the displacer, and it's moving just as much as it was at slow speeds.

https://youtube.com/shorts/AvZ_GvFu8xE? ... faO4EBcnvt

I'll repeat test with better lighting and higher temperatures. Will the response time and piston travel be this good at higher temperature deltas?

https://www.vaia.com/en-us/explanations ... ideal-gas/


Thanks to Tom's determination I now know that free expansion does not use a 1 bar buffer pressure as a baseline and instead uses a vacuum.

I also now know that PV=nRT applies to a free expansion.

That also means I have been comparing my observed real world expansion ratios to an unobtainable value. My results then are even better than I had thought.

The next step then is to introduce a perfectly sealed and thermally well designed power piston, evacuate some air and see how close we can come to the ideals in page 2 of this thread.
viewtopic.php?t=5572&hilit=Calculating&start=15

Not that I want to confuse issues, but one criticism I have (edit: a couple actually) of that resource is;

...after going to great lengths to explain over and over again that the temperature of the gas in a "free expansion" does not change they go on to provide this example:

Application 1: Refrigeration Refrigeration systems operate on the principle of free expansion. In such systems, a refrigerant gas experiences high pressure, and when it's allowed to expand suddenly to a region of lower pressure, it cools down.

They just said ten times that the temperature does not change, but put forward this "application"; refrigeration without hesitation or explanation, although it appears to be a contradiction of the entire concept and everything stated before and after, leaving one incredulous.

Thermodynamics is, unfortunately full of so many contradictions of this sort, when I see something said regarding "ideal gas" behavior, I tend to take it with a grain of salt. Basically I read "ideal" generally as "in the land of make believe".

You'll find a more in depth treatment and explanation for this apparent contradiction, however, studying up on the Joule Thomson effect.

Some gases, useful refrigerants, get (a little) colder during free expansion, but other gases actually get warmer. This has to do with the molecular forces of attraction of the particular gas involved.

The molecules of light gases like helium and hydrogen repel strongly, if I recall correctly, so the repelling force puts work into the gas as it expands, causing it to warm up, gain some kinetic energy from this kick of repelling force.

Most other gases have attractive forces dominating so on expansion do work breaking away from the attractive forces resulting in cooling, loosing some kinetic energy as they pull away from the attractive force.

Some of the gas looses so much energy in trying to pull away, it doesn't make it, so condensed back into a liquid.

In all cases, however, the determining factor is "work".

Joule Thomson cooling however (ordinary refrigeration) is a relatively slight effect. A refrigerator has to circulate the refrigerant repeatedly to achieve a substantial cooling effect. Having a gas expand into a vacuum and having it do additional work, other than expanding against its own molecular attractive force, work, such as driving a piston or a turbine, results in much more rapid cooling.

That this resource does absolutely nothing to guide the reader to more in depth information or otherwise explain such a stark and blatant contradiction is, ...

Well, par for the course, unfortunately.

But I've said several times before in here, according to the "ideal gas law" there is no such thing as refrigeration, heat pumps or air conditioning.

According to the ideal gas law, a gas expanding into a vacuum (Joule Thomson cooling) does not change temperature at all.

Application 2: Car engines A gasoline engine works under the principles of thermodynamics, where fuel-air mixture in the cylinders undergoes a rapid increase in temperature and pressure. This heated gas expands, pushing the pistons to do mechanical work - driving the car. These examples explain the role of free expansion of an ideal gas in the everyday mechanisms around us.

With this, "application" example, I'm completely gobsmacked.

How is this an example of "free expansion" without the gas doing any work, and without a temperature change?

There are even more contradictions in that article than what you mentioned Tom. This permeates almost every aspect of science (and life for that matter), and I'm sure even holds true at a university level.

All I can do is test my own ideas and theories. As I like to say, I finished watching Game of Thrones, so I have some free time anyway.

Misleading ways of describing things are just that, misleading. Humans are prone to mistakes when writing. Go figure.

I guess when I went to college I had an understanding that all books contain errors. So far that attitude hasn't changed, nor found any necessity to change.

The Joule Thompson temperature reduction effect is interesting. Since I have no reason to build anything using that effect, I haven't studied it much. Helium and hydrogen were first liquified using the effect. It requires that they are cooled down below a certain temperature where the effect is effective. I do know how cooling from work, cooling from the Joule Thompson effect, and cooling from cooling temperature difference, is represented on a TSPH diagram. To me adding in entropy and enthalpy makes those processes very confusing.

A free expansion would be if all the walls vanished suddenly and all molecules continue in the direction and speed they were going. No slowdown, no temperature drop. Ideally.

Real gases and real environments cause slowdown. The center gas pushes the outer gas doing a little work for a little cooling. The outer gasses receive work speeding up, so are hotter. Refrigerators capitalize on this by the gas going through the orifice, hitting slower moving gas that is being 'retracted' by the pump, doing a little work on the slower gas causing the faster gas to cool. But that is only a thought.

Around 1870, Linde 'discovered' the refrigeration cycle. Prior commercialization, while teaching at Heidelberg, his star student was Rudolf Diesel who wasn't interested in refrigeration. After commercialization, Linde gave Diesel the Paris dealership (of Linde), so that Diesel could finance his engine research.

Fool - I've been waiting for you/someone to point out Tom's obvious flaw on work producing cyro temps. A free energy mindset has an obvious agenda, and this cold hole BS is a common fantasy.

Using expansion work to aid cooling sounds simple, but approaching zero K, any "work" potential shrinks, compression or expansion. This favors a compression cycle engine, but disfavors an expansion reefer cycle. Near zero K:

(1) Req'd dV during adiabatic expansion dwarfs dT, so the main gimmick remains megabar P prior expansion. Any online adiabatic calculator should illuminate massive dV issue (I scale from my adiabatic index cheat sheet).

(2) A small turbine expanding into a large vacuum (volume) will NOT have liquid whatever forming like water rolling off a duck's back where a constant vacuum drives expansive work that drives upstream compressor. Despite bogus free energy pitch, no 'gas' turbine can tolerate liquid, so final 'drip' will always be JT.

matt brown wrote: ↑Sat Jul 06, 2024 3:02 pm ...

Fool - I've been waiting for you/someone to point out Tom's obvious flaw on work producing cyro temps. A free energy mindset has an obvious agenda, and this cold hole BS is a common fantasy.

Using expansion work to aid cooling sounds simple, but approaching zero K, any "work" potential shrinks, compression or expansion. This favors a compression cycle engine, but disfavors an expansion reefer cycle. Near zero K:

(1) Req'd dV during adiabatic expansion dwarfs dT, so the main gimmick remains megabar P prior expansion. Any online adiabatic calculator should illuminate massive dV issue (I scale from my adiabatic index cheat sheet).

(2) A small turbine expanding into a large vacuum (volume) will NOT have liquid whatever forming like water rolling off a duck's back where a constant vacuum drives expansive work that drives upstream compressor. Despite bogus free energy pitch, no 'gas' turbine can tolerate liquid, so final 'drip' will always be JT.

Do you spend sleepless nights trying to dream up your strawman arguments to discredit "Tom".

Nothing better to do with your life?

Since when does work output from a Stirling engine reducing the temperature of the working fluid have anything to do with "cryo temps"?

I'm talking about ANY "cooling" from work output, as opposed to heat transfer to a "sink" or "cold reservoir".

A free energy mindset has an obvious agenda

Heat engines work by converting heat into work. That requires HEAT. No "free energy" No "agenda".

The only one here with an agenda appears to be you. To slur, defame and discredit "Tom Booth".

Why is that Matt?

Inquiring minds want to know.

(2) A small turbine expanding into a large vacuum (volume) will NOT have liquid whatever forming like water rolling off a duck's back where a constant vacuum drives expansive work that drives upstream compressor. Despite bogus free energy pitch, no 'gas' turbine can tolerate liquid, so final 'drip' will always be JT.

A largely irrelevant technical detail, but if you had been following the history and development of the use of expansion turbines for liquifying gases, you would know that this is wrong: "A small turbine expanding into a large vacuum (volume) will NOT have liquid whatever forming..."

I won't bother addressing the rest of your long run-on sentence.

Turbines were used for cooling to extract "work" and gas did sometimes liquify, even before leaving the turbine.

Later advances led to delaying liquefaction, using Joule Thomson cooling for the final liquefaction stage so the expensive turbine would last longer, not because it isn't possible.

None of this has anything to do with "free energy"

The technical details of the final stage in modern gas liquefaction does not in any way negate the fact that expansion turbines are used to "extract work", from the gas, which carries out the bulk of the cooling.

So what if JT is used for the "final drip"?

All this has no real bearing on a Stirling engine other than the basic principle involved, that an expanding gas, made to do work as it expands drops in temperature, joule for Joule just "as if" heat were being removed.

U = Q - W

Matt Brown wrote:Fool - I've been waiting for you/someone to point out Tom's obvious flaw on work producing cyro temps. A free energy mindset has an obvious agenda, and this cold hole BS is a common fantasy.

I don't think it will work. He has already rejected many parts of 1800's Classical Thermodynamic scientific discoveries and data. It's easy to tell by his usual standard denial lines and vituperation, that he is probably too far gone to benefit from anything I can provide.

From Wikipedia, "Entropy (classical thermodynamics)":

https://en.m.wikipedia.org/wiki/Entropy ... entropy%20(from,spontaneous%20changes%20in%20the%20system.


To go from gas to liquid a process has to go from above the red dome to inside the red dome. Moving towards the left inside of the dome produces more liquid, to the right is zero liquid. The Joule-Thompson cooling follows the blue constant enthalpy lines. Those lines must cross into the red dome. To get the Claude process it follows the vertical constant entropy lines. They also must cross into the red dome to get liquid.

The following is a markup of where two of those processes can start:
#1 red box, is where the Linde process must start to enter the dome and liquify. Notice it requires 50 to 200 atmospheres. And temperatures below 160 K.

#2 orange box, is atmospheric temperature and pressure. The blue, Linde lines, go to the right and further away from the dome as a vacuum is pulled. Also the adiabatic, Claude, line going straight down also misses the red liquid/gas dome.

This is empirical proof that a standard temperature and pressure gas can't be limited by pulling a vacuum with free expansion or with work.

This is empirical proof that gases always push, irregardless of pressure or temperature. Unless at Zero Kelvin. Back-work will always be significant. I've tried to point this out many ways.

Fool wrote: ↑Sun Jul 07, 2024 9:12 am ...

This is empirical proof that a standard temperature and pressure gas can't be limited by pulling a vacuum with free expansion or with work.

....

Proof?

The paragraph doesn't even make any sense.

"standard temperature and pressure gas can't be limited..."

What do you mean by "limited"?

Like nearly all your posts, pure gobbledygook. A meaningless, indecipherable throwing of spaghetti against the wall hoping something sticks that might make "Tom" appear to be wrong.

Wrong about what? Who knows?

It doesn't really matter. Just so long as there is an appearance of having been discredited

The real target of attack is my experiments, which speak for themselves, are observably irrefutable and easily reproducible.

REAL science uses scientific methodology. Which ultimately involves testable theories and actual experiments. Not just being a blowhard, making declarations of opinions as if they were proven fact.