Search found 116 matches
- Thu May 16, 2024 8:35 am
- Forum: Stirling and "Hot Air" Engine Forum
- Topic: The TRUTH? η = 1 – (Qc / Qh) = 1 – (Tc / Th)
- Replies: 581
- Views: 29106
Re: The TRUTH? η = 1 – (Qc / Qh) = 1 – (Tc / Th)
Charles law states V1/T1 = V2/T2 So if we have a 1cm^2 tube with 100cc of air under the piston, then we need to double its volume to lift our piston by 1m. If we start with 300K air then 100/300 = 200/T2 = 600K 3.65 Joules are needed to raise 100cc of air from 300K to 600K We used 1J raising the 10...
- Wed May 15, 2024 7:57 am
- Forum: Stirling and "Hot Air" Engine Forum
- Topic: The TRUTH? η = 1 – (Qc / Qh) = 1 – (Tc / Th)
- Replies: 581
- Views: 29106
Re: The TRUTH? η = 1 – (Qc / Qh) = 1 – (Tc / Th)
Here's my contention with the absolute zero thing, the best we can do on earth is exhaust down to 1atm at 300k or so. So chasing "100%" efficiency is like a baseball player chasing a 1.0 batting average, when .300 is considered excellent, and .400 is unheard. Instead, re-framing "100...
- Wed May 15, 2024 2:01 am
- Forum: Stirling and "Hot Air" Engine Forum
- Topic: The TRUTH? η = 1 – (Qc / Qh) = 1 – (Tc / Th)
- Replies: 581
- Views: 29106
Re: The TRUTH? η = 1 – (Qc / Qh) = 1 – (Tc / Th)
Fool,
My supposition regarding Tom's observations is that we shouldn't consider it to be an engine at all, rather it is a self-powered heat-pump, since it doesn't drive a load, and therefore the only work it can do is 'internal'.
My supposition regarding Tom's observations is that we shouldn't consider it to be an engine at all, rather it is a self-powered heat-pump, since it doesn't drive a load, and therefore the only work it can do is 'internal'.
- Tue May 14, 2024 9:06 am
- Forum: Stirling and "Hot Air" Engine Forum
- Topic: The TRUTH? η = 1 – (Qc / Qh) = 1 – (Tc / Th)
- Replies: 581
- Views: 29106
Re: The TRUTH? η = 1 – (Qc / Qh) = 1 – (Tc / Th)
Tom, The "absolute zero" thing is a core part of the definition of efficiency for a fuel-powered engine - if the exhaust is at any temperature above absolute zero then there is energy being wasted. It's a particularly poor definition for Stirlings, with the many possible energy sources, bu...
- Mon May 13, 2024 9:50 am
- Forum: Stirling and "Hot Air" Engine Forum
- Topic: Tesla's Ambient Heat Engine revisted
- Replies: 230
- Views: 3249
Re: Tesla's Ambient Heat Engine revisted
I think the difference in temperature in a Stirling engine is largely time dependent. (What part of the cycle). I'm quite happy to accept that that is true, but only if someone can point me at some science that says how fast temperature equalises / quantifies a temperature gradient in the working f...
- Mon May 13, 2024 8:26 am
- Forum: Stirling and "Hot Air" Engine Forum
- Topic: Tesla's Ambient Heat Engine revisted
- Replies: 230
- Views: 3249
Re: Tesla's Ambient Heat Engine revisted
Atmospheric pressure across the entire globe varies very little from 14.7 psi Good point. However that is exactly why we have wind - air mass "moving itself" in order to equalise _pressure_ differences caused (largely/entirely?) by temperature differences. Which rather brings me back to t...
- Fri May 10, 2024 2:38 am
- Forum: Stirling and "Hot Air" Engine Forum
- Topic: Tesla's Ambient Heat Engine revisted
- Replies: 230
- Views: 3249
Re: Tesla's Ambient Heat Engine revisted
If that is truly the case, then the gas laws imply that the temperature of the fluid must also be equal, everywhere. This is another case where it helps to think of energy flow into the engine, rather than heat. Glad when you chime in Mike B. I think this ties in nicely with your thoughts on "...
- Thu May 09, 2024 3:59 am
- Forum: Stirling and "Hot Air" Engine Forum
- Topic: Tesla's Ambient Heat Engine revisted
- Replies: 230
- Views: 3249
Re: Tesla's Ambient Heat Engine revisted
It's just one wishy-washy sequence in essentially an open chamber. The gas is free to move around. Even with the displacer fully raised, convection causes the cold gas to sink and be replaced by hot gas, which in turn is cooled, and again sinks. I know I mentioned the speed of sound before, but as ...
- Tue May 07, 2024 7:14 am
- Forum: Stirling and "Hot Air" Engine Forum
- Topic: Tesla's Ambient Heat Engine revisted
- Replies: 230
- Views: 3249
Re: Tesla's Ambient Heat Engine revisted
"Pretty obviously the elevated heat signature appearing around the power piston could only be from "work"."
Why is that?
Could the heat not come from the working fluid?
Why is that?
Could the heat not come from the working fluid?
- Fri May 03, 2024 9:21 am
- Forum: Stirling and "Hot Air" Engine Forum
- Topic: Heating a LTD Stirling engine efficiently
- Replies: 5
- Views: 199
Re: Heating a LTD Stirling engine efficiently
If you do want to have the two faces have matching grooves, then think about using casting for one or both.
- Fri May 03, 2024 6:33 am
- Forum: Stirling and "Hot Air" Engine Forum
- Topic: Tesla's Ambient Heat Engine revisted
- Replies: 230
- Views: 3249
Re: Tesla's Ambient Heat Engine revisted
Tom, IIRC you were the first to mention fridge's. We seem to be in agreement that they have little relevance to this discussion. Average <anything> is ALWAYS a thing, and while it may not be entirely easy to predict, the average temperature of the working fluid of a hot-air engine is definitely a th...
- Thu May 02, 2024 9:15 am
- Forum: Stirling and "Hot Air" Engine Forum
- Topic: Tesla's Ambient Heat Engine revisted
- Replies: 230
- Views: 3249
Re: Tesla's Ambient Heat Engine revisted
For heat to be removed from the cold end, by the working fluid, it must have an _average_ temperature throughout the cycle, that is below that of the cold end. It's easy to postulate that the working fluid temp might drop below that temp briefly, but I'm really struggling to see how it could be bel...
- Tue Apr 30, 2024 4:31 am
- Forum: Stirling and "Hot Air" Engine Forum
- Topic: Stirling engine speed/accelleration control
- Replies: 4
- Views: 339
Re: Stirling engine speed/accelleration control
Not something I've actually tried yet, but my idea is to de-couple the displacer from the power piston, and instead drive it with an electric motor. In theory, the speed of the engine would directly follow the speed of the displacer, and of course if the electric motor is stopped completely, the eng...
- Tue Apr 30, 2024 4:28 am
- Forum: Stirling and "Hot Air" Engine Forum
- Topic: Tesla's Ambient Heat Engine revisted
- Replies: 230
- Views: 3249
Re: Tesla's Ambient Heat Engine revisted
For heat to be removed from the cold end, by the working fluid, it must have an _average_ temperature throughout the cycle, that is below that of the cold end. It's easy to postulate that the working fluid temp might drop below that temp briefly, but I'm really struggling to see how it could be belo...
- Thu Apr 25, 2024 8:41 am
- Forum: Stirling and "Hot Air" Engine Forum
- Topic: Stirling-Apha heat pump, and finned pistons
- Replies: 6
- Views: 671
Re: Stirling-Apha heat pump, and finned pistons
I think you've already noticed, but the big issue with any alteration / increase of surface area is that it tends to also increase the dead volume, which is generally considered "a bad thing" but maybe its a worthwhile trade-off?