Stirlingengineforum.com

So during the expansion stroke the gas is in contact with Tc? That is backwards of an engine. Also it will gain heat faster in compression and potentially end up hotter than Th and cost more work than that earned by expansion. The PV diagram makes it easy to visualize this.

Stroller wrote: ↑Thu May 02, 2024 11:18 amMy favourite Feynman quote:
" I'd rather have questions that can't be answered, than answers that can't be questioned."

My thanks to you, Tom, Vince and everyone contributing here. I've run a forum where thermo discussions got far too heated (Lol) and resulted in explosions and ejections from the solar system. This place is the model of civility by comparison.

I like that quote too. And "You will fool yourself more often than anyone else."

I like Tom too. I fear his patience is wearing thin for reading points that support classic theory, and contradict his.

Fool wrote: ↑Thu May 02, 2024 2:25 pm ...
I like Tom too. I fear his patience is wearing thin for reading points that support classic theory, and contradict his.

An understatement.

"Classic theory" is 100% garbage that should have been taken out to the curb and forgotten at least a century ago.

That it's still being advocated with gusto, with seals of approval from top universities as absolute incontrovertible "established science", makes presenting simple facts that contradict the prevailing narrative a seemingly futile endeavor.

Regardless, It would be derelict of me not to at least try.

Fool wrote: ↑Thu May 02, 2024 2:24 pm So during the expansion stroke the gas is in contact with Tc?

The working fluid is shifted from the hot side to the cold side about 1/2 the way to BDC (between full compression and full expansion), so yes. for the latter mostly adiabatic phase after most of the heat input has been used up (converted to work and momentum)

That is backwards of an engine.

Since when?

Also it will gain heat faster in compression and potentially end up hotter than Th

Yes, potentially.

Actually a good thing if you think about it.
Very high heat and compression at TDC, just when needed.

and cost more work than that earned by expansion.

Not really. Your converting work input by atmosphere from velocity back into heat at TDC to "launch" the piston with the next expansion.

The PV diagram makes it easy to visualize this.

PV diagrams do not show all the dynamics involved.

Stroller wrote: ↑Thu May 02, 2024 11:45 am

Tom Booth wrote: ↑Thu May 02, 2024 11:36 am hot air has no chance of putting enough heat into the engine. Just glanced off, but doesn't penetrate. Too much air volume. Not enough concentrated heat.

What you need is a big parabolic mrror and a sunny day. How difficult is it to build one do you think? By chance I visited a place in the foothills of the Pyrenees in France where they set up a solar reflector system in the 1970s. It ran a steam turbine to generate eleccy back then. These days, it's used to wallop secretive ceramic mixtures with 4000K.

Well, maybe someday. The enormous weight of the thing is an issue trying to suspend it above a dish. Tracking.

Before investing any more in it I want to at least see if it can run. Nearly 20 years old, but apparently never used. Stored in some university closet all these years.

I think it may require a jolt of electricity to the linear generator to "bump' it into action, but is supposed to self-start (sometimes, maybe, if your lucky)

I think possibly direct heat from a rather large propane flame might get it to do something.

Something like this maybe?

Fool wrote: ↑Thu May 02, 2024 12:42 pm Simple to build large parabolic dish refector:

https://m.youtube.com/watch?v=8CLRTa_ocmo

I suppose they could be made hexagonal and with cheap black or clear tarp and use contact cement to glue aluminum foil to it before stretching and vacuuming.

Another method for making parabolic mirrors. This one uses a spun aluminium satellite dish.
https://www.youtube.com/watch?v=W3TcRuExonk

Tom Booth wrote: ↑Thu May 02, 2024 7:42 pm

Something like this maybe?

Compress_20240502_224103_3928.jpg

Maybe that and keeping the coolant flow minimal until the engine is running strongly. The Infinia CEO says they initially used an engine from a propane fired generator set to prototype the solar generator. How different that was I don't know.
1:15 in the vid you linked before: https://www.youtube.com/watch?v=EBidoWN-9Us

My point really was that it's a good example of how NOT to build a Stirling engine.

Personally, I'm skeptical it ever worked at all.

The solar input area is nearly adjacent to the water jacket.

6000° metal alloy tungsten or whatever hot enough to vaporize stainless steel contiguous with a cooling jacket containing water that boils at 212° maybe a little higher with some additive.

How is that going to work out?

Unfortunately, I've never been able to find specifications. If the minimum operating temperature is 600° maybe it used some high temperature heat transfer fluid for "coolant". With water it could never reach operating temperature without boiling.

Tom Booth wrote: ↑Thu May 02, 2024 6:14 pm

Fool wrote: ↑Thu May 02, 2024 2:24 pm So during the expansion stroke the gas is in contact with Tc?

The working fluid is shifted from the hot side to the cold side about 1/2 the way to BDC (between full compression and full expansion), so yes. for the latter mostly adiabatic phase after most of the heat input has been used up (converted to work and momentum)

That is backwards of an engine.

Since when?

Also it will gain heat faster in compression and potentially end up hotter than Th

Yes, potentially.

Actually a good thing if you think about it.
Very high heat and compression at TDC, just when needed.

and cost more work than that earned by expansion.

Not really. Your converting work input by atmosphere from velocity back into heat at TDC to "launch" the piston with the next expansion.

The PV diagram makes it easy to visualize this.

PV diagrams do not show all the dynamics involved.

At 1/2 the expansion stroke, the displacer is tight against the cold plate and all the gas is in the hot space. The displacer has bottomed out and is in the process of reversing directions. The piston is moving outwards, expanding, at its highest rate with the gas in the hot space.

Transfer of the fluid from hot to cold only begins at that point and is at the displacers slowest speed. It is further retarded if there is a lost motion link involved that delays it until the piston is much closer to the bottom and mostly finished with expansion, as Senft's LTD is. The transfer only begins there and is at its lowest rate, barely happening.

The transfer is barely 1/2 done when the piston is at bottom dead center and the piston is moving slowest. At that point the displacer is at full speed, where the transfer from hot to cold is the highest.

Your description would not surprise me if it were nonfunctional.

Your description is backwards since the very first descriptions by the Stirling Brothers of their first engines. Gas is mostly in the hot space for expansion, and mostly in the cold space for compression.

Work from the atmosphere was removed during expansion and saved momentum from expansion is lower because of it. Return stroke atmospheric work cancels with forward stroke atmospheric work. They are equal and opposite and cancel each other. No net work gain from atmospheric pressure.

Return stroke momentum is higher from the atmospheric work than it would be in a vacuum, but forward work is lower than if in a vacuum by the same amount. The two cancel out each other.

All the atmosphere does is provide a U-turn for free. Momentum-out is now momentum-in. And that momentum energy gets completely eaten up by the return stroke's compression. The piston stops at top dead center, zero momentum, Th, V1/V2, P2. 100 J DQh, 400 J Qhz, 400 people pushing outward. Just another free U-Turn. Ideally.

PV diagrams can be useful for explaining ideal models. Indicator diagrams of real engines, responding to any dynamics the system responds to, show a lesser cycle with a lower efficiency shape, all well within the better/best shaped ideal maximum efficiency PV plot. In other words PV and indicator diagrams agree well, and are consistent, meaningful and useful tools for people that 'get it'. For those that don't, who cares.

Dismissing them without valid data, is science denial. Scientific scepticism is important. Denial isn't.

Your experiments warrant being sceptical. They don't warrant denial/dismissal/bashing.

Tom Booth wrote: ↑Fri May 03, 2024 3:42 am Unfortunately, I've never been able to find specifications. If the minimum operating temperature is 600° maybe it used some high temperature heat transfer fluid for "coolant". With water it could never reach operating temperature without boiling.

They wouldn't have used water because of the risk of frost damage. It may well have been designed to use silicone oil, which has a boiling point around 315C

Stroller wrote: ↑Fri May 03, 2024 6:49 am

Tom Booth wrote: ↑Fri May 03, 2024 3:42 am Unfortunately, I've never been able to find specifications. If the minimum operating temperature is 600° maybe it used some high temperature heat transfer fluid for "coolant". With water it could never reach operating temperature without boiling.

They wouldn't have used water because of the risk of frost damage. It may well have been designed to use silicone oil, which has a boiling point around 315C

When I first got the engine and started examining it I pulled off the cooling system hose and a green fluid came out, that "looked like" ordinary 50/50 automotive antifreeze.

At any rate, the solar dish, reportedly concentrated sunlight 800-to-1:to nearly 4000°F (not 6000° sorry)

Sunlight gets concentrated in an 800-to-1 ratio, which would raise the temperature at the heat-resistant nickel-alloy concentrator to 2,000°C if the Stirling generator didn’t extract heat from it and keep it at about 650°C, says Tim Talda, Infinia’s director for system electronics and controls.

I just noticed:

The PowerDish uses an electric pump and fan-cooled radiator to circulate about a gallon of a 50/50 water/glycol mix around the Stirling generator’s cool side.

I guessed the reason the hot receiver and water jacket are so close together was that the displacer travel is relatively short moving at 60Hz ?

The article I'm referencing though contradicts my assumption.

Inside the generator, the working fluid, high-pressure helium, quickly heats up and expands, sending the displacer on its forward stroke of about 7 in. Meanwhile, the hot helium is shunted to the cold side of the engine where it contracts and quickly loses pressure and temperature. A mix of properly tuned gas and mechanical springs sends the displacer back and helps it maintain smooth, back-and-forth resonant harmonics. The displacer cycles at about 60 Hz and travels at 15 fps.

7 inches?

Not sure if that is the actual distance the displacer moves, that seems very unlikely, next to impossible for flexure bearings vibrating at 60Hz but who knows.

Could be some mix up or confusion of facts by the reporter.

The actual engine I have has the water jacket barely more than 2 inches behind the solar receiver. Something doesn't add up.

Source:

https://www.machinedesign.com/markets/e ... nditioning


At any rate, in my efforts to get the thing going, heating the receiver with a 1000 watt electric hot plate, the water/antifreeze circulating began heating up immediately.

Pretty obviously to me, that heat was being CONDUCTED through the engine body into the coolant. Heat is being immediately wasted, thrown away.

The cooling system requires a circulating pump, radiator and fan. I could heat my shop with the "waste heat" before even getting the thing hot enough to start.

A horrific waste of heat/fuel IMO, unless you just want a solar hot water heater.

Maybe they found a good use for it before going bankrupt?

https://vimeo.com/44817732

Heating swimming pools?

Though it isn't clear if the intention was to have the dish heat the water directly via circulating water through the engine or by generating electricity to power electric water heaters...

The dish in the video appears to still have its radiator and cooling fan installed.

Anyway, I can see for myself the engine I have immediately dumps heat apparently straight into the cooling water.

That is heat wasted that will never be converted into anything by the engine. An enormously energy wasteful design, by all appearances and testing.

How it could ever even get up to operating temperature without blowing up the cooling system with steam I don't know.

Maybe once started, if I can ever get it started, the engine converting heat to power output keeps the temperature low and draws heat away from the cooling system.

The article says:

Sunlight gets concentrated in an 800-to-1 ratio, which would raise the temperature at the heat-resistant nickel-alloy concentrator to 2,000°C if the Stirling generator didn’t extract heat from it and keep it at about 650°C, says Tim Talda, Infinia’s director for system electronics and controls.

The question is, how much of the heat being "extracted" is being converted to electricity and how much is just wasted through the cooling system?

"Generator" implies electric output.

A 1350°C ∆T provided by conversion of heat into electrical power output is how it sounds to me, which is in harmony with some other source information.

A patent application I found a long time ago, for example stated that if the load was reduced, such as a sudden drop in power usage on the grid (everybody switching off their air conditioners for example) the engine would "quickly overheat".

In other words, the conversion of heat into electricity "siphons off" heat AS electricity or converted into electricity thus reducing the temperature.

No way water cooling is going to draw off 1350°C continuously all by itself I don't think.

In other words, a good chunk of the "cooling" is through heat conversion rather than heat removal to a rather diminutive cooling system.

Fool wrote: ↑Fri May 03, 2024 6:15 am ....

You've made a number of very important and highly significant talking points, which I've highlighted here.

I'll comment on them all in full another time.

Fool wrote:Pulling a vacuum on a plugged syringe requires an input of work, the gas inside expands doing work for an adiabatic temperature drop. The work input by pulling, plus the work output by the gas, are both absorbed by the atmosphere, changing it negligibly, storing the energy as a spring. The springiness is cause by the difference in pressure inside and out.

After expanding the gas from point two and, Th, V1/V2 and P2 to T3, V3 and P3/Atmospheric/P1, Tom wants to continue expanding adiabatically until the gas reaches Tc. This will be similar to the instructor pulling on a plugged syringe.

This will diminish the pressure below atmospheric, producing an inward force. An extra outward force must be applied as energy into the engine. It could come from the outgoing energy from the momentum, using up that energy. If all the forward stroke gained energy is used, the volume will double at the point where the piston stops from that decelerating force.

Inside pressure 200 will be half the starting pressure 400. Temperature will be lower than Th. And momentum will be zero. The energy earned in the forward stroke, momentum, will be spent and stored in the force pushing inward. Similar to a spring.

The piston now moves inward accelerating. The gas heats up from compression. At the half way point, again the gas will be T3,V3, P3, and the same amount of energy will be stored in momentum going inward.

The atmosphere only provides a free U-turn. Now the momentum is being used to recompress the gas. Pressure inside 400 gets higher than outside3
300. The temperature continues to rise adiabatically. The momentum is used up when back at T2, V2/V1, and P2. The starting point of the expansion. Zero work can be output.

Atmospheric pressure 300, temperature 300 and volume (infinite) remain almost unchanged at all points of the cycle. A negligible change.

Fool wrote: ↑Sun May 05, 2024 2:53 am
...Now the momentum is being used to recompress the gas...

Geez Fool, you've been sucked in with bad buzz.

Tom enjoys using momentum as another magic energy source, but momentum is NOT energy (go ahead and google that). Any momentum that the piston/flywheel/etc "absorbs or releases" is from the kinetic energy of the engine and ambient gasses. The work area of PV plots do not require ambient pressure for validity, since ambient buffer pressure cancels out across a cycle. Suggesting one can steal energy via ambient backstroke ranges from ill informed to lunacy. Likewise, any piston 'momentum' cross cancels in a similar way. For laymen, the head game is nothing more than considering the piston has no mass, whereby momentum nonsense disappears.