Liquid Heating/Cooling of Hot/Cold Alpha Stirling Engine Cylinders?

[MikeB]

That is going to be a difficult question to answer, and potentially counter-intuitive too!
A load of tarmac will certainly heat up a lot in direct sun, but not sure how good the heat conductivity would be - if there is too much insulating effect (as with the compost heap) then you won't get much transfer to your engine, unless you use a huge surface area - and maybe you can do that cheaply, maybe not?

On the other hand, this isn't a new problem - when I was a lad, a solar panel meant a bunch of tubes on someone's roof, used to directly (?) heat water for bathing. One can assume that a "solar hot water panel" like that would be about as efficient as you can get.

[JessIAm]

The point of using tarmac is the heat retention of the tarmac. Think of it as an equivalent to "cold retention" of a running stream of water.

If you had pipes snaking through or under the <insert thing that gets hot but releases heat slowly here>, you could use water or some other coolant to draw the heat away efficiently enough to heat the hot cylinder of the Stirling engine.

The thing that releases heat slowly could be tarmac, a large chunk of basalt rock, a large heat sink like basalt with a wood fire on it, compost heap, ...

The innovation being how the heat or cooling is delivered to the Stirling engine. This would allow the Stirling engine itself to run more consistently (not necessarily efficiently, but efficiently enough), and deliver consistent power to whomever needs it.

I don't believe heating or cooling conveyance has been looked into much.

If consistent heating and cooling for the Stirling engine is approached cleverly, than the efficacy of Stirling engines for supporting society increases.

Note: I wrote this early in the morning before waking up, and hopefully my use of italics isn't dramatic or offensive.

[Tom Booth]

That's the strength I see of this - the ∆T comes from two theoretically inexhaustible sources - the mountain stream, and the well tended compost heap.

Whoa! The stream is a great source of cooling, but the compost heap not so much, nowhere near to inexhaustible in fact! The point is that you need two different things from a heat-source/cold-sink, and absolute temperature is only one of them! The other is volume - the stream has plenty, but if the compost heap was actually producing a lot of _Energy_ then it would still be heating up.

Did you see this video posted earlier?

https://youtu.be/-Jm-c9B2_ew

20 hot showers a day for two months from one compost that took a couple hours to build sounds like a fairly decent heat source, especially if the compost material is freely available and the finished compost is needed anyway.

The compost heap in that video was, presumably, not tended at all, just built and left to do its thing.

Unlike the sun, a compost produces heat 24/7.

It doesn't keep getting hotter and hotter because it is a living, biological source of heat that maintains a fairly even temperature.

[Tom Booth]

A rather long, detailed study on heat from compost as an energy source can be found here:

https://www.hindawi.com/journals/ijce/2010/627930/

At the end it concludes: "It can therefore be concluded that collecting the waste heat of compost through a heat exchanger is a realistic solution to contributing to energy demand."

Better "more reliable" than either solar or ground source heat pump used for comparison in the study.

"The system was found to provide the most reliable supply of the three systems, and to do so at a very competitive price"

[JessIAm]

That's the strength I see of this - the ∆T comes from two theoretically inexhaustible sources - the mountain stream, and the well tended compost heap.

Whoa! The stream is a great source of cooling, but the compost heap not so much, nowhere near to inexhaustible in fact! The point is that you need two different things from a heat-source/cold-sink, and absolute temperature is only one of them! The other is volume - the stream has plenty, but if the compost heap was actually producing a lot of _Energy_ then it would still be heating up.

Did you see this video posted earlier?

Yep!

I guess I'm looking at the subject of the thread and asking what other ideas than compost people can come up with for a heat source.

[JessIAm]

A rather long, detailed study on heat from compost as an energy source can be found here:

https://www.hindawi.com/journals/ijce/2010/627930/

At the end it concludes: "It can therefore be concluded that collecting the waste heat of compost through a heat exchanger is a realistic solution to contributing to energy demand."

Better "more reliable" than either solar or ground source heat pump used for comparison in the study.

"The system was found to provide the most reliable supply of the three systems, and to do so at a very competitive price"

BOOYAH! Thanks for the reference!

[Tom Booth]

That's the strength I see of this - the ∆T comes from two theoretically inexhaustible sources - the mountain stream, and the well tended compost heap.

Whoa! The stream is a great source of cooling, but the compost heap not so much, nowhere near to inexhaustible in fact! The point is that you need two different things from a heat-source/cold-sink, and absolute temperature is only one of them! The other is volume - the stream has plenty, but if the compost heap was actually producing a lot of _Energy_ then it would still be heating up.

Did you see this video posted earlier?

Yep!

I guess I'm looking at the subject of the thread and asking what other ideas than compost people can come up with for a heat source.

The question was intended for MikeB.

Composting really can be an "inexhaustible" source of heat so long as there is raw material available.

Back when I did a lot of composting for growing garlic commercially I kept large piles of high carbon material (brown dry leaves, sawdust) and high nitrogen material (manure, green grass clippings, weeds) in separate piles.

These piles would not really begin to compost and get really hot until mixed together.

Lawn care people seem to be always looking for places to dump leaves and grass clippings, In the country here, there is no shortage of manure.

Anyway, as composting needs a balance of carbon and nitrogen, the piles of material can be kept and mixed for use in composting as required. By rotating piles, this could be a source of continuous heat.

In that article they only make use of the hot air rising from the compost rather than the compost itself.

I'd probably put a copper coil of pipe to form a chimney up the center of the pile.

horse-manure-a-renewable-resource-swinker-29-728.jpg (75.8 KiB) Viewed 8046 times

Image source:

slideshare.net/heyboerg/horse-manure-a-renewable-resource-swinker


I used to use a length of perforated sewer pipe just to vent the pile.

[JessIAm]

I'd probably put a copper coil of pipe to form a chimney up the center of the pile.

horse-manure-a-renewable-resource-swinker-29-728.jpg

Image source:

slideshare.net/heyboerg/horse-manure-a-renewable-resource-swinker


I used to use a length of perforated sewer pipe just to vent the pile.

Hm... I wonder if you could get some sort of natural water circulation with that? Heat doesn't change water density that much, but it does change a little bit. The Navy uses that for ultra quiet nuclear submarines.

So, since you're in the country, what can you cobble together to make a prototype of this?

[Tom Booth]

So, since you're in the country, what can you cobble together to make a prototype of this?

Ah, well, I would really really love to, and have a good location for it.

The only real problem would be finding, or making the time for it. I've got so many different projects going now already.

[JessIAm]

Fair enough! :)

[Tom Booth]

I just happened across this video depicting the type of simple two tin cans in hot and cold water baths type heat engine.

This variation uses a Ross yoke. This is the first I've seen one of these type of engines actually running.


https://youtu.be/JbCTIEJYruU

[Tom Booth]

I'm thinking there might be a number of ways of improving the power & efficiency.

The HOT side cans, pretty obviously, will lose a lot of heat to the OUTSIDE ambient air. The bottom can continuously and the inside can every time it is lifted out of the water.

The hot water bath can could be insulated to retain heat.

The inner hot can could be made of plastic on the outside with an inner metal lining. That might help transmit heat to the air INSIDE without losing so much heat to the outside. An aluminium or copper inner lining might work better than tin.

A problem of water vapor condensing in the transfer pipe and eventually stopping air flow is mentioned in the video as a problem. Water is strongly attracted to salt, so a salt water bath would probably have less evaporation. Some cooking oil could also be floated on the water to help prevent evaporation. Not sure how that might effect heat transfer though.

The original patent cited earlier suggests using a bundle of tubes rather than a single pipe for more surface area, I would think also making the inner metal lining of the hot can corrugated would do likewise.

A high efficiency regenerator in the transfer pipe.

Much as an LTD engine has a large diameter displacer, I would think using cans with greater diameter would likewise have greater potential for increased surface area, which might allow operation at much lower temperature difference.

Making the "cans" as light weight as possible. I was thinking of trying plastic with an inner lining of aluminium foil.

Frankly, trying to increase surface area by hanging a bunch of wires from the can being lifted seems like a bad idea as it increases the weight the engine has to lift. A bundle of tubes in the water bath as in the patent does not create that problem of increased weight.

Using a bundle of flattened out tubes could increase surface are while not increasing dead air space so much as round tubes.

Perhaps the lifters could also be counterbalanced in some way? Springs? Magnets?

I think that probably the diameter of the transfer pipe and regenerator should be a large diameter so as not to restrict air flow.

Anything else?

[airpower]

Ross yoke linkage machines operate on 120° thermodynamic angle instead of the conventional 90°
No matter what all require at least 35° Fahrenheit (1.67°C) temperature difference to operate.
This engine has 3 spoke flywheel 1 is displacer bottom dead, 2 is working bottom dead, 3 both fully retracted
Unfortunately also has the flywheel cancer


https://www.youtube.com/watch?v=-qbn9bI1JzY

[Tom Booth]

From observing the video, I think there is something wrong with the timing and / or length of the throw.

As the hot can goes up and air expands, the cold can should be going up also, far enough to allow the air to fully expand.

It looks however like this is not happening. As the hot can goes up, the cold can too quickly starts to go down so the engine is working against itself almost continuously. I'm not sure if this is due to the Ross yoke or what. Possibly adjusting the pin driving the yoke further out on the diameter of the flywheel would give more simultaneous lift. Or, the problem may just be that due to trying to hold the camera in one hand while working the valve, the flywheel was not in the right position when he closed the valve so there was not enough air in the line.

[Tom Booth]

...
No matter what all require at least 35° Fahrenheit (1.67°C) temperature difference to operate.

Your conversion is not correct.

A 1.67°C ∆T translates to about 3 or 3.5°F (or is that 35 a typo? Missing decimal point?)

According to Senft, some LTD engines were able to operate on less than 1°C (less than 2°F ∆T)

[Senft, JR. (2007). Mechanical Efficiency of Heat Engines. Cambridge, UK: Cambridge University Press.]