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

[JessIAm]

Maybe make a compost next to the creek and do something like:

IMG_20210417_134805858_resize_75.jpg

Sorry, I tend to get carried away with these ideas sometimes.

Don't be sorry! Your enthusiasm is why I'm here! :D

I like your interpretation of my idea. I'll need to do some drawing and show what I mean to be explaining.

[Tom Booth]

Maybe you've heard of Jean Pain.

20 hot showers a day for two months from one compost pile sounds like a lot of hot water! If it is only being recirculated through the pile to heat hot water to run a Stirling engine it should do quite well.

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

Anyway, there's lots of information on Jean Pain's methods for getting energy from compost on the internet.

https://smallfarms.cornell.edu/2012/10/compost-power/

[JessIAm]

Maybe make a compost next to the creek and do something like:

IMG_20210417_134805858_resize_75.jpg

Sorry, I tend to get carried away with these ideas sometimes.

I've been trying to draw my own design, which is complicated by my wear induced arthritis.

Here's how I would change your drawing:

Have the hot/cold cylinders in an Alpha Stirling Engine with a single crank case.

Have pipes:

• Coiled within the Compost Pile
• Pipes connecting the compost pile coil and the hot cylinder coil
• Coiled around the hot cylinder

Water flows in the pipes to collect the heat from the compost pile, and heat the hot cylinder. This is the heating loop.

Make a similar system for the cooling system:

• Coiled within a stream or some other cooling source
• Pipes connecting the cooling source coil and the cold cylinder coil
• Coiled around the cold cylinder

Like the heating loop, water flows in the cooling system pipes to cool the cold cylinder.

[Tom Booth]

Maybe make a compost next to the creek and do something like:

IMG_20210417_134805858_resize_75.jpg

Sorry, I tend to get carried away with these ideas sometimes.

I've been trying to draw my own design, which is complicated by my wear induced arthritis.

Here's how I would change your drawing:

Have the hot/cold cylinders in an Alpha Stirling Engine with a single crank case.

Have pipes:

• Coiled within the Compost Pile
• Pipes connecting the compost pile coil and the hot cylinder coil
• Coiled around the hot cylinder

Water flows in the pipes to collect the heat from the compost pile, and heat the hot cylinder. This is the heating loop.

Make a similar system for the cooling system:

• Coiled within a stream or some other cooling source
• Pipes connecting the cooling source coil and the cold cylinder coil
• Coiled around the cold cylinder

Like the heating loop, water flows in the cooling system pipes to cool the cold cylinder.

Nice concept. I get the general idea. My only real concern is that a conventional Alpha V type Stirling engine has limited surface area for heat exchange, which usually necessitates a rather extreme temperature difference. That is, a lot of high heat concentrated in the relatively small area at the piston head. The tight seals required on the pistons also introduce more friction than other options.

The Gamma type Stirling with large, virtually frictionless dispacer with a lot of surface area for heat exchange is probably more suitable for such a low temperature application.

On the other hand, I've been very impressed by the engines TK Motors has designed, what seems to me to be a new type of Stirling engine, which he is calling "diaphragm Alpha", using rather large diaphragms, rather than pistons.

The small tin can engines run, reportedly, with a lot of torque, on as little as a small tea candle flame.

These TK engines are unusual in that the regenerator is stationary, the "displacer" is only an internal membrane, so the surface area can be very large without requiring the lifting of any large heavy weight displacer.

Of course a candle flame is still probably hotter than a compost, but a tea candle is a very tiny heat source compared with the blow torch type flame often required to run a conventional Alpha type Stirling.

https://youtu.be/AOwY3nFOey8

[JessIAm]

The Alpha Stirling Engine was chosen because it's easier to heat and cool separate cylinders, and because I read the cooling stroke is also a power stroke for the Alpha.

Perhaps the Alpha Stirling Engine needs heating and cooling sources with more of a temperature difference?

The basic idea of heating and cooling the cylinders with separate loops of coolant is still sound:
The idea is the heating loop and the cylinder it heats would reach an equilibrium temperature, thus always keeping the hot cylinder hot (same for the cooling loop and cylinder).
This will result in fuel savings, as it would take less fuel to keep the hot loop at a given hot temperature.

This is basically applying the principles of a heat pump to the heating and cooling of the cylinders of an Alpha Stirling Engine.

[Tom Booth]

Perhaps the Alpha Stirling Engine needs heating and cooling sources with more of a temperature difference?

I don't think I've ever seen a V style alpha Stirling running with anything less than a flame of one sort or another. Usually something like a propane torch, so I'm guessing that it might be difficult to have one run on something like heat from a compost, though I've never tried it and wouldn't necessarily rule anything out.

An LTD type Stirling on the other hand is designed specifically for low temperature difference operation, so it would almost be guaranteed to at least run, probably.

The basic idea of heating and cooling the cylinders with separate loops of coolant is still sound.

Of course.

Any type Stirling engine has a hot side or end or cylinder and a cold side/end/cylinder of some sort. Using a different type of Stirling engine does not alter the basic concept.

[JessIAm]

Perhaps the Alpha Stirling Engine needs heating and cooling sources with more of a temperature difference?

I don't think I've ever seen a V style alpha Stirling running with anything less than a flame of one sort or another. Usually something like a propane torch, so I'm guessing that it might be difficult to have one run on something like heat from a compost, though I've never tried it and wouldn't necessarily rule anything out.

An LTD type Stirling on the other hand is designed specifically for low temperature difference operation, so it would almost be guaranteed to at least run, probably.

The basic idea of heating and cooling the cylinders with separate loops of coolant is still sound.

Of course.

Any type Stirling engine has a hot side or end or cylinder and a cold side/end/cylinder of some sort. Using a different type of Stirling engine does not alter the basic concept.

Part of my goal with this suggestion is to use a much more efficient method to heat/cool the appropriate cylinders. Using a blow torch relies on air to transfer the heat, which is not a good temperature transfer medium. Coolants would be much more efficient, and therefor require less fuel.

Also, if the compost heap produces 130 to 150 F, and the cooling loop keeps the cold cylinder at 40 F, you have a 90 to 110 F temperature difference for the Stirling Engine. I don't know if that is a low temperature or high temperature difference in Stirling Engine parlance.

[MikeB]

40 degrees F is kind of mid-range territory for a tea-cup model - some LTD engines can go as low as 4 degrees or so.
On the other hand, for a power-producing machine it is tiny - they tend to operate with more like 400 degrees difference, so don't expect to run your house off it!

Without knowing how much heat your compost provides, I can't do a full calculation, but for every litre of 40 degree water you can pump through, you have a max of 26Wh available, assuming 100% efficiency...

[JessIAm]

Note the 40 F is an estimation of the temperature of the cooling source, not the temp difference. According to internet, the temp that came up most for compost heaps is 130 to 150 F.

The temp difference would be about 100 F.

The strengths of this system are consistency and the lack of a fuel fire. Since the compost heap is always producing heat when healthy, the hot cylinder would eventually be the temperature of the compost heap. Similarly the cold cylinder would remain at a low temperature. This is because the loops of coolant (or heat-ant?) would reach an equilibrium temperature, and tend to keep their corresponding cylinder at that temperature.

[JessIAm]

For a long time I've been hoping to find the time to try building one of this type Stirling engine, that might be adapted to your project.

Basically, it runs on hot and cold water.

Maybe it could be scaled up by using 30 and 55 gallon drums or something instead of just tin cans.

Screenshot_20210417-042838.jpg

I don't anticipate that it would produce much power, but should be inexpensive and uncomplicated.

I totally missed this from before. This is such a cool idea. Seems a little inefficient, since the camshaft is longer since the cylinders are separated. Still, pretty cool!

[Tom Booth]

40 degrees F is kind of mid-range territory for a tea-cup model - some LTD engines can go as low as 4 degrees or so.
On the other hand, for a power-producing machine it is tiny - they tend to operate with more like 400 degrees difference, so don't expect to run your house off it!

Without knowing how much heat your compost provides, I can't do a full calculation, but for every litre of 40 degree water you can pump through, you have a max of 26Wh available, assuming 100% efficiency...

I'm wondering, theoretically, a Stirling engine can run on cold. (Not theoretical really, it can, sort of)

Anyway, it would be possible to run a Stirling engine on cold water alone. Take this "Ultra LTD" for example:

https://youtu.be/ARD3ctp80ac

Of course, that engine is REALLY running on ambient heat, or the ∆T between the cool wet paper and the warmer ambient.

Another idea I've wanted to try for a long time is a small desktop novelty Stirling that would sit on a bedside table and pump water for a little fountain. Just running on the ambient heat in the room and the evaporative cooling of the little water fountain.

So many ideas and so little time.

Anyway, the point is, I'm not sure how it would be calculated exactly, but the cold water provided by the stream could, in theory, keep a Stirling engine running without the additional heat from a compost.

A flowing stream could absorb a virtually unlimited amount of "excess heat", which is something that needs to be taken into consideration when figuring energy output.

Likely the NEGATIVE heat, or cold provided by the limitless cold of the stream would provide more potential power output than the finite heat from the compost.

Also, a low ∆T does not necessarily mean extremely low power.

The Sun Pulse, just an oversize LTD engine puts out 500 watt to - 1.5 kw

https://youtu.be/v_e0981CLDI

[JessIAm]

40 degrees F is kind of mid-range territory for a tea-cup model - some LTD engines can go as low as 4 degrees or so.
On the other hand, for a power-producing machine it is tiny - they tend to operate with more like 400 degrees difference, so don't expect to run your house off it!

Without knowing how much heat your compost provides, I can't do a full calculation, but for every litre of 40 degree water you can pump through, you have a max of 26Wh available, assuming 100% efficiency...

Of course, that engine is REALLY running on ambient heat, or the ∆T between the cool wet paper and the warmer ambient.

Anyway, the point is, I'm not sure how it would be calculated exactly, but the cold water provided by the stream could, in theory, keep a Stirling engine running without the additional heat from a compost.

A flowing stream could absorb a virtually unlimited amount of "excess heat", which is something that needs to be taken into consideration when figuring energy output.

Likely the NEGATIVE heat, or cold provided by the limitless cold of the stream would provide more potential power output than the finite heat from the compost.

Also, a low ∆T does not necessarily mean extremely low power.

The Sun Pulse, just an oversize LTD engine puts out 500 watt to - 1.5 kw

MikeB, you got it in 1! 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. Note: A large black stone absorbing sunlight could also work for the heat source.

I like the Sun Pulse. Do you have a source link for that engine?

[Tom Booth]

I like the Sun Pulse. Do you have a source link for that engine?

There is a patent and various other links here:

viewtopic.php?f=1&t=2541

There seems to have been some talk of commercialization years ago, but that doesn't seem to have gone anywhere, that I know of.

[MikeB]

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.

[JessIAm]

What would be good sources of heat then? I'm thinking a large basalt slab painted black - or a stretch of road that stays in the sunlight most of the day.