Stirlingengineforum.com

I have a few questions on stirling engine refrigeration. When you turn a stirling engine with a motor, I assume the cold side is still the cold side? If this is correct you would want to put your water bath at the hot end? Does the stirling produces some kind of internal pressure the colder it gets ? Or can you use a small motor geared up to get more rpms? I read somewhere the trick to getting the coldest temp. is rpms, somewhere around 8000 rpm. Approtechie, ran his water bottle diaphragm stirling engine with an electric motor and got a reading of 36f in a Styrofoam box. Do you think you could use a wind turbine as the power source?

As long as you run the motor in its normal direction, the hot end of the displacer becomes cold, and the cold end becomes hot, requiring lots of cooling. looking at my photo album, you will see my second engine, James G. Rizzo's Dyna, I'v used that to drive the Ross Yoke motor, down to -20*C, that took about 20 minutes, With more power, and revs the temperature could be dropped a good bit more. Ian S C

Ian S C; Thank you for your response. Iam a bit confused by {running in its normal direction] The piston and displacer go up and down.Do you mean the flywheel must turn clockwise or counter clockwise?

Hey fullofhotair,
This is how I look at it. Hopefully some of what I write is of use to you.
I'll refer to a conventional beta design for my explanation

Forward (normal direction)
when the engine is running forward the 'displacer' is located 90 deg ahead (or whatever set degrees), of the power piston with regards to crankshaft rotation...
(this can be clockwise or anti-clockwise, it all depends on how you set the crank up, or how you view it)
The expansion space is located at the top of the engine (top of displacer)
The compression (or contraction) space is at the bottom (between power piston and displacer)

Backwards (reverse direction)
when the engine is running backwards, it swaps, and the 'power piston' is now located 90 deg ahead (or whatever set degrees), of the displacer with regards to crankshaft rotation...
(again this can be clockwise or anti-clockwise it all depends on how you set the crank up, or how you view it)
The expansion space is now located at the bottom (between power piston and displacer)
The compression (or contraction) space is now at the top of the engine (top of displacer)

Its not really a case of clockwise or anti clockwise. Its dependant on what's in 'front',.
for example: if you walk around 180deg and look at the engine from the other side, the direction of spin appears to suddenly change, at least from your new perspective, but the engine is still obviously spinning in the same direction, and the same component is still running in 'front'.

A stirling can perform 4 functions

1. Hot gas engine (runs forward)
2. Refrigerator (driven forward)

3. Cold gas engine (runs backwards)
4. Heater pump (driven backwards)

Rule of thumb, That i use: The overall majority flow of energy Always migrates from the Expansion space and is transferred to the compression (contraction) space, for all 4 functions.

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Forwards
The expansion space is located at the top of the engine (top of displacer)
The compression (or contraction) space is at the bottom (between power piston and displacer)
Therefore: Energy will migrate away from the head.

1. Hot gas engine (runs forward)
When you heat the head, the flow of heat is from the expansion space (at top) to the compression space (at bottom)
( this is why you must heat the head to keep the engine running (energy is migrating away from the head) )

2. Refrigerator (driven forward)
When you drive the engine forward the heat flow is again from the expansion space (at top) to compression space (at bottom).
(this is why the head gets cold (energy is migrating away from the head))

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Backwards
The expansion space is now located at the bottom (between power piston and displacer)
The compression (or contraction) space is now at the top of the engine (top of displacer)
Therefore: Energy will migrate towards the head.

3. Cold gas engine (runs backwards)
When you cool the head, the flow of heat is still from the expansion space (now at the bottom) to the compression space (now at the top)
(This is why you must now cool the head to keep the engine running (energy is migrating towards the head))

4. Heater pump (driven backwards)
When you drive the engine backwards the heat flow is again from the expansion space (at bottom) to compression space (at top).
(this is why the head gets hot (energy is migrating towards the head))

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Now that’s all probably as clear as mud. I hope my explanation doesn't sound like gobbledygook.
Its how I've learnt to look at things...
Feel free to completely ignore it if it doesn't help.

It might be worth playing around with this animated beta engine to go with the explanation.
If you pause it on the web-page you can grab the slider to run it backwards or forwards, for a 360deg rotation.
http://www.animatedengines.com/stirling.html


This example is running in the Forward (normal) direction
as the displacer is travelling in front, on the crank

vamoose

Vamoose;
That explained it very nicely for me ,thank you. It does raise one more question though. Is there any useful applications for the cold gas engine?

Comecially the cryocooler is used for producing liquid gas ie., dry ice/ liquid Nitrogen is the common one, but other frozen gasses, often for laboritory use. They are also used for cooling electronics, computers etc, and instruments on satilites. Ian S C

Vamoose, posted (stirling magazine articles) It had an article on a free piston stirling refrigerator, using the compression vapor cycle. The article stated that unit was inexpensive to build and had only 2 moving parts. It was also efficient. That sounds like winning combo to me.

fullofhotair, simple is a relative explanation of it, simple compaired to what? What was the generator in a free piston motor now becomes a linear motor driving the piston, but if it was really cheap and efficient, everyone would have one. Ian S C

Ian SC, This unit is different. It doesn't use the stirling cycle to cool. Heat runs the free piston stirling engine ,which drives a linear compressor. Freon was the coolant. Hydrogen the working gas.