SpudFiles

Greetings, I am a immigrant from the old spudtech forum. I came here looking for some troubleshooting help with my latest project; a test tube sterling engine. The air in the test tube is definitely expanding, the problem is that the syringe is not retracting or the air isn’t cooling. I can’t figure out why the syringe isn’t retracting as the air cools. Here are 2 videos. The first one is how the test tube engine should work. The second video is how mine works. Does anyone have any ideas as to why the expands but doesn’t contract.
Thanks for the help
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Welcome (back?) to the spudding community

Most likely the marbles you're using are too tight a fit in the test tube.

1 thing that came to my mind. 1. The rate of expansion, (how fast/slow your heating the air).

That's what it looks like to me.

Edited for what was I thinking.

In the first video the flame is touching the test tube, whilst yours is a good 1" 1/2 below. Add items under the flame jar so the flame touches your test tube thus giving you more heat. see if that works.

You have too much heat and too little cooling. As the system warms overall with time, the working gas volume becomes larger until is quits cycling. With less heat, the average temperature will be lower. The cycling is carrying the heat to the cold side and it is overwhelmed.

The hints are the very aggressive start up with a good cold side and the gradual expansion of the working gas as the warm side overheats and the cold side becomes warm. The result is too much gas volume and the end of cycling.

As the displacer warms, it contributes to the heating of the cold side.

Traditional displacer sterling cycle engines is insulated so it does not carry heat to the cold side. Only the working gas caries the heat as the displacer moved. A traditional displacer sterling cycle engine is not 100 % sealed so it will adjust the working gas volume over a wider temperature operating range than a sealed syringe which has a narrow operating temperature range.

1 more thing I just noticed, the test tube in the 1st video looks longer.

Perhaps you put to many marbles in the tube.
I love sterling engines and perpetual motion machines.
Take a look at this sterling engine,it is running on hand heat.

That engine is of the traditional design with an insulated displacer and a non-sealed piston cylinder. As the engine becomes warmer overall, some working gas escapes past the piston and piston rod. As the overall temperature cools, more air can work its way in. A sealed (airtight) system does not have this temperature latitude. As the overall temperature rises above the operating range, the expanded gas biases the movement to one side where it stalls if it becomes too warm. It also won't run if it is too cold.

The rubber piston syringe is a high friction part. Note the top one is using another seal. Do you have any glycerin to lube the rubber?

Technician1002 wrote:Traditional displacer sterling cycle engines is insulated so it does not carry heat to the cold side. Only the working gas caries the heat as the displacer moved. A traditional displacer sterling cycle engine is not 100 % sealed so it will adjust the working gas volume over a wider temperature operating range .........

Good to see people are interested in Sterlings. Here's one I did several years ago.
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Thanks for the help everyone, I thought about some of the suggestions and Technician and jacks were right. Here is what I found

1) The marbles are so snug in the test tube that they are practically water tight.
2) The test tube is overheating because the syringe has too much friction. Thermal expansion wont move it until the whole engine is too hot.

I tried using 2 cycle oil to lubricate the syringe but the pressure somehow causes it to jam. I think that oil is getting trapped between the rubber plunger and the cylinder.
I also tried using automotive grease but the plunger just wiped it clean.
I then relieving the rubber plunger of rubber by sanding it with a fine knife sharpening stone. I ended up with a shredded plunger with so many little tears that it jammed in the cylinder.

Any ideas on making a small pneumatic cylinder to replace the syringe.
The one in the first video is glass and is hard to find in the U.S.
Thanks

Get some 1/2" or 3/4" pvc and get a threaded rod with some washers to seat an o-ring.

http://i979.photobucket.com/albums/ae27 ... M_1098.jpg

If you make a close fit piston such as the one in my Mouse Musket with very little gap. The gap can be sealed with a layer of grease. They seal well with capilary action holding the grease and work at low pressure. It is the same thing as used in model boat stuffing boxes.

slimecoat wrote:I tried using 2 cycle oil to lubricate the syringe but the pressure somehow causes it to jam. I think that oil is getting trapped between the rubber plunger and the cylinder.
I also tried using automotive grease but the plunger just wiped it clean.

Bad idea, syringe seals tend to absorb these sort of lubricants and expand, causing even more friction.

Any ideas on making a small pneumatic cylinder to replace the syringe.
The one in the first video is glass and is hard to find in the U.S.
Thanks

Cast it out of epoxy. It will be practically airtight but with much less friction.