Tom Booth wrote: ↑Thu May 02, 2024 7:23 am
I need to construct engines that actually run and produce practical power. My NASA engine has abysmal thermodynamics. All the heat is transfered straight into the cooling system. You need a 15 foot parabolic dish and full sun, about 6000° concentrated on a point the size of a softball just to get it started for a measly 3k about 800 lbs of cold heat conducting steel and copper conducting 80% of the heat straight through to the water jacket to produce zero power.
Well that paragraph got my attention.
You have some beast of a sun-tracking parabolic mirror powered Stirling in your backyard? I want to see the pics!
What is 3k referring to? Did you miss a W there? It's making 3kW from a 15 foot dish? Impressive, since 12.56 m^2 of mirror is capturing a mere 12kW of solar energy at zenith on a clear day. That's a Carnot approved 25% efficiency! If you made that kind of investment, you must surely at least have a spreadsheet of useful data logs?
Tom Booth wrote: ↑Thu May 02, 2024 7:23 am
I need to construct engines that actually run and produce practical power. My NASA engine has abysmal thermodynamics. All the heat is transfered straight into the cooling system. You need a 15 foot parabolic dish and full sun, about 6000° concentrated on a point the size of a softball just to get it started for a measly 3k about 800 lbs of cold heat conducting steel and copper conducting 80% of the heat straight through to the water jacket to produce zero power.
Well that paragraph got my attention.
You have some beast of a sun-tracking parabolic mirror powered Stirling in your backyard? I want to see the pics!
What is 3k referring to? Did you miss a W there? It's making 3kW from a 15 foot dish? Impressive, since 12.56 m^2 of mirror is capturing a mere 12kW of solar energy at zenith on a clear day. That's a Carnot approved 25% efficiency! If you made that kind of investment, you must surely at least have a spreadsheet of useful data logs?
Sorry the engine was missing the dish. I've been trying to get it running but no conventional heat source I've thrown at it so far has been enough to get it started.
Nearly all the heat goes straight into the cooling water, but not using cooling water could damage the heat sensitive linear generator.
The only option is to put way more heat in faster than the cooling system can take it away. Totally designed around Carnot heat rejection principles where even at 25% efficiency, 75% or the supplied heat is wasted through the cooling system.
You need about 10,000 watts + of heat input for "up to" 3,000 electrical output.
Fool wrote: ↑Thu May 02, 2024 5:08 am
Thermodynamics gets very intertwined with itself and difficult to keep straight. Everything seems to change with one little change. Write one thing, and it means something else in another engine. Try to be generic and it will fail to apply in another engine. Talk about boiling, and it contradicts evaporation. Work-in becomes work-out. Sign convention changes in every process, it seems. Complexity becomes too simple. Simple becomes too complex. Tom seems to have difficulty with it too so I cut him and everyone lots slack. I read and reread my posts and it is still unreadable, and correct, and incorrect, all at the same time, it seems. That is why I started quoting Feynman.
My 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.
Tom Booth wrote: ↑Thu May 02, 2024 11:14 am
Nearly all the heat goes straight into the cooling water, but not using cooling water could damage the heat sensitive linear generator.
The only option is to put way more heat in faster than the cooling system can take it away. Totally designed around Carnot heat rejection principles where even at 25% efficiency, 75% or the supplied heat is wasted through the cooling system.
You need about 10,000 watts + of heat input for "up to" 3,000 electrical output.
Stirling engines are tricky beasts which have to be tailored to their purpose. Your NASA engine is indeed tuned to receive 10kW or more of solar energy to work. I'm beginning to understand your position and chagrin.
It's not going to be easy, but a carefully fan blown charcoal fire should be able to hit the hot end with the required heat input. You're just going to have to protect the rest of the beast from the blow-by, because the Sun and mirror concentrate the heat just where it's needed, without scorching anything else.
Otherwise, you could consider a ramjet running kerosene with a suitable re-radiating diffuser between the fiery blast and the ht end plate, but then you'd lose the Stirling USP of low noise.
Last edited by Stroller on Thu May 02, 2024 11:37 am, edited 1 time in total.
If you view that thread you'll see the thing is covered with a slew of thermocouples that happen to be compatible with my reader, so I can get temperature readings easily.
coupler4.JPG (233.63 KiB) Viewed 2015 times
The cooling water heats up immediately when heat is applied to the receiver. Getting the engine hot enough to start up with water circulating 2" behind the receiver seems to be a loosing battle.
Tom Booth wrote: ↑Thu May 02, 2024 11:14 am
Nearly all the heat goes straight into the cooling water, but not using cooling water could damage the heat sensitive linear generator.
The only option is to put way more heat in faster than the cooling system can take it away. Totally designed around Carnot heat rejection principles where even at 25% efficiency, 75% or the supplied heat is wasted through the cooling system.
You need about 10,000 watts + of heat input for "up to" 3,000 electrical output.
Stirling engines are tricky beasts which have to be tailored to their purpose. Your NASA engine is indeed tuned to receive 10kW or more of solar energy to work. I'm beginning to understand your position and chagrin.
It's not going to be easy, but a carefully fan blown charcoal fire should be able to hit the hot end with the required heat input. You're just going to have to protect the rest of the beast from the blow-by, because the Sun and mirror concentrate the heat just where it's needed, without scorching anything else.
I've tried a 140,000 BTU kerosene heater, seen around the middle of this video:
but 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.
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.
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.
Tom Booth wrote:During the return stroke the gas is cold and TAKES IN heat rapidly rather than "rejecting" heat.
How does it absorb heat if the compression stroke starts at Tc? Even if starting with a deeper expansion it will be above Tc before it gets back to where Tc was for the expansion direction because it has absorbed some heat. The rest of the compression will be above Tc leading to heat rejection for most of the stroke.
