Modified Gama cycle(cold hole/ambient scheme warning)

[VincentG]

Ok guys I have another crackpot hot air scheme to prototype. Initial pressure gauge testing is encouraging to say the least! This is the culmination of my dive into the ambient/wind engine that is largely based on mass flow here viewtopic.php?f=1&t=5545 and testing on a fixed volume displacer cylinder to understand available pressure v. heat input here viewtopic.php?f=1&t=5539 and here viewtopic.php?f=1&t=5549. Links added for future reference.

The goal here is to make use of pressure AND mass flow, something pistons can't do.

I have to say I was largely inspired by Tom's take on self cooling cycles and especially his recent foray into air cycle machines, as well as Matt's deep dive on Gamma's. This modified cycle seems to be easy to construct and optimize. It should also work better at very large scale, and should benefit greatly from higher temperature input.

It also benefits from slow displacer cycle rates to improve heating and cooling times, while maintaining a constant utilization of energy flow.


Consider a STANDARD gamma type displacer cylinder(300k-600k) with the hot plate covered. Power piston at TDC and a 300k 1atm+compression ratio as a starting point, move displacer to cover cold plate and we heat air volume to 600k and drive piston toward BDC. Lets assume(for arguments sake) the work done on the piston drops gas temperature back down to 300k by BDC. (Back to ambient or colder and crank power is now being robbed from the engines output.)

So now atm pressure drives the piston back towards TDC, but only until internal pressure reaches 1atm, after that we have to put in the work of compressing the gas again.

I would argue that this is a relatively idealized cycle and would require careful balancing of compression ratio and displacer cylinder to power cylinder size, and varying load will affect the outcome as well.



Now, for the modified Gama cycle.

Again consider the starting point of displacer covering hot plate, only this time there is only 1atm at 300k and there is no piston.

Move displacer to cover cold plate. The volume of air is heated and allowed to leave the displacer cylinder via one-way check valve and flow to turbine or reciprocating free piston(think pneumatic air hammer). This air will dump to open atm so lets run it through multiple stages to extract all heat energy, anything left can go towards domestic hot water use. As far as I'm concerned, this is near 100% utilization of heat.

atmopheric lung hot.jpg (107.23 KiB) Viewed 7179 times

Next, move displacer to cover hot plate. The effluent check valve has closed. What we are left with is a displacer chamber in a state of vacuum. The higher the Tmax, the less air will be left in the chamber, helping to make the next cycle even more efficient. The residual heat in the remaining volume of air is all that would be needed to be cooled externally. With intermittent heat input and a well designed hot sink, this could be reduced to a minimum.

With the hot plate covered and the chamber otherwise fully insulated, another one way check valve now allows ambient air to flow into the air cycle turbine that is connected to the same shaft as the hot turbine. The atmospheric air drives the cold turbine, adding power output and simultaneously lowering temperature to below ambient before it is allowed to expand into the displacer chamber and possibly further reduce in temperature.

atmospheric lung cold.jpg (110.6 KiB) Viewed 7179 times

The influent check valve has now closed and we now have 1atm at a Tmin of BELOW AMBIENT air to start the cycle over again in a "supercharged" state, all while extracting power from ambient heat and pressure.

This cycle can easily benefit from tuned port ram air effect for both intake and exhaust scavenging. Also, the "atmosphere" can be replaced by a pressurized vessel of sufficient size(large enough to not be effected by operating volume of engine) and increase power further.

[matt brown]

There's only a few heat process options and each have PVT constraints. If this scheme started with an isothermal process then expansion would be 600k and pressure would drop proportional volume change. But, when expanding to 300k, the only option is adiabatic, and the process values for this are derived via gamma function (exponential Cp/Cv) touched on in that recent cold tube video you posted. Hmmm, bottom line for diatomic air is that adiabatic expansion with 2x temperature drop is begging for 6x volume rise with 12x pressure drop. Houston, we have a problem...

[VincentG]

Good call Matt, the self cooling part was a bit pie in the sky and not needed for the cycle to function anyway.

In bench testing, the main advantage here is total usage of displacer chamber airflow and no work lost to compression or over expansion.

Using only hot water, I was able to reach pressure swings above what I saw before on a full boil.

[Bumpkin]

There’s at least one way to make a turbine that’s not directional and eliminate the need for check valves. I’ve pondered a twin rotary displacer engine with a flat flexible-vane fan-type turbine between. It would turn the same direction no matter the air flow direction.

Bumpkin

[Tom Booth]

This looks a lot like what I was working on here:

viewtopic.php?f=1&t=461&p=3034#p3032

Posts titled "Stirling Pump" and the next after that.

Unfortunately the mpeg video format isn't supported by many browsers any more and the image remote links don't show up in some browsers any more. I did convert the video and uploaded it to YouTube though.

I just now made this drawing to show the inner construction of this "pump".

Resize_20230812_094236_6748.jpg (269.73 KiB) Viewed 7125 times

And the YouTube video of it "working".

https://youtu.be/S8MBj6_sdSw

There were many problems with this experiment. My homemade check valves were very crude and leaked. At the time I had not considered the conductivity of the coffee can. The top of the can got cold very quickly and stayed cold, heat conducting through the metal rather than the air inside. Unlike a turbine, the balloon creates a continually increasing back pressure. I had to pre-inflate the balloon as it would knock the ballbearing off the check valve when deflated, so the pump was working against back pressure from the start.

The little side chamber for the check valves is all copper which would also tend to put a drain on any ∆T developed.

I always meant to do some follow up experiments but considered this crude demonstration enough of a "proof of concept" so never bothered. The thing was soldered together so not easily modified or repaired.

Anyway I thought you might find that interesting.

[VincentG]

Matt, I understand that maybe we won't get cooling directly from expansion, but the cooling effect of the ACM seems to be a sure thing from my research. This is cooling that would normally be wasted on the back side of the piston on the return stroke, now being applied directly to the cycle.

I'll look into that style turbine Bumpkin, but I think the uniflow air path with no check valves would lead to inefficiencies in temperature mixing and airflow.

Thats pretty cool Tom and pretty close to what I'm going for. Maybe you saw that I titled the pictures "atmospheric lung".

Just did some testing over boiling water and saw pressure swings that were double that of the engine in normal operation, and this is with no work lost to compression or expansion. Allowing the displacer chamber to fully charge with cold air and fully discharge with hot air effectively doubles its working displacement as compared to standard Stirling engine operation.

At this point I believe that the compression and expansion work can be achieved purely as a function of ram air effect in tuned length intake and exhaust runners. Even add to that the effect of hot air rising and cool air falling.

Look at the incredible supercharger like gains made with this outrageous tunnel ram intake. With stationary power units we have the benefit of fixed RPM operation too.

https://www.youtube.com/watch?v=y9IERetMoL4

[Tom Booth]

...the self cooling part was a bit pie in the sky...

...

I disagree.

If you can have a displacer chamber acting as a pump then you could have a refrigeration cycle.

That is either open or closed cycle.

A refrigeration system is essentially a "pump" (compressor) with some form of throttling device (a simple "pinch" or narrowing of the pipe, an expansion valve, expansion engine or expansion turbine) between the high pressure "exhaust" and low pressure "intake".

Pump, compressor, engine... Mechanically all more or less the same.

And don't forget heat is generated on the high pressure side before the gas is expanded to the low pressure side.

I've got probably half a dozen or more (theoretical) drawings or designs for "self cooling" with such a "pump" or "lung".

Bottom line is if you have a pressure differential between inlet and outlet you have the makings of an ACM.

[VincentG]

You may be right Tom. I'll wait for further testing to make any real claims but it seems promising to me.

[Tom Booth]

This is a real old drawing, same basic coffee can shape.

Air_Stirling_Gen.jpg (26.99 KiB) Viewed 7062 times

The idea is basically to use this "lung" pump or Stirling compressor to compress air into a refrigeration type tube (condenser).

The gas is held back by the turbine nozzle so pressure builds in the tubes releasing heat, which the "pump" then uses to pump more air.

The air is cooled and compressed, but the heat is not wasted, as in a refrigerator condenser, the "rejected" heat goes right into compressing more air.

At the turbine nozzle the compressed and cooled air is converted into a high velocity stream to power the turbo-generator.

The resulting cold "exhaust" from the turbine is used to increase the ∆T of the "Stirling compressor" by cooling the cold side, theoretically, below ambient if possible, which then allows, or in theory, results in more ambient heat becoming available.

With what I know now, I think I would design this a little differently.

[VincentG]

I missed your post somehow Tom. Good idea though.

This guy is great and constantly testing new ideas. This latest one can be directly applied to using a large gamma chamber as a lung. I imagine he will show some low pressure power output numbers.

https://youtu.be/DiNRHgMnfyo

As of late I've been thinking of two chambers that are arranged to flow between each other with separate one way conduits. This could double effective working pressure with the same delta temperature.

[Tom Booth]

I missed your post somehow Tom. Good idea though.

This guy is great and constantly testing new ideas. This latest one can be directly applied to using a large gamma chamber as a lung. I imagine he will show some low pressure power output numbers.

https://youtu.be/DiNRHgMnfyo

As of late I've been thinking of two chambers that are arranged to flow between each other with separate one way conduits. This could double effective working pressure with the same delta temperature.

3 volts from just "lung power" is pretty impressive.

About a year ago I picked up several really small cheap pneumatic air powered wrenches from harbor freight, with the idea of getting out what I imagined must be some kund of turbine. Instead I found small compact rotary vane motors. Those cheap ones though, required a considerable volume of air to get going. At low pressure the air would just go straight through.

Peter Lindemann posted an idea for a kind of two chamber, two displacer rotary hot air engine that could probably be constructed out of some 55 gallon drums. (Or tin cans for that matter).

This was his illustration of the idea:

Resize_20230823_141339_9266.jpg (146.58 KiB) Viewed 6838 times

http://www.energeticforum.com/forum/ene ... post403413


Something like that could probably be modified with one way valves or "fluid diodes" to drive a turbine in the manner you are suggesting.

[Tom Booth]

Peter's original post with the drawing was apparently moved, the forum pages shuffled around or something.

Anyway, if interested I found the original page on the Way ack archive (post #7)

https://web.archive.org/web/20191109115 ... rling.html

[Tom Booth]

Maybe something like two of these rocket stoves with the 55 gallon drum Stirling rotary engine/turbines on top

https://youtu.be/w8hAF92aOVg?si=C1AqwmDrLrKrHPl7

[VincentG]

Thanks Tom definitely food for thought. I think the rotary displacer is inefficient but its definitely simple.

I wonder how the vane motors would hold up to high temperature air. They may make quite a bit more power on high temp air if they can extract heat energy like a turbine. Regardless, I'm leaning towards a tesla turbine for this design.