Im in machineshop classes at my local college, and my teacher has a
Stirling engine he built and I plan to make one soon, I understand
how it works, but am completely lost when I take it from heat and
put it on ice and it slows, then runs backwards....I understand that
heat rises and is pushing on the piston, and the cold is alowing the
heat above to be pushing down, but no matter the source it is still
just moving up and down with a central connecting rod....so what
makes it run backwards? well even more what makes it directional, it
seems that either way you get it spinning it should keep going that
way.
Heat runs one way, cold the other....im confused
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stan.hornbaker
- Posts: 532
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Heat Always Flows From Hot TO Cold
No need to be confused. Heat always flows from a region of high temperature, the Source, to a region of low temperature, the Sink.
In normal operation heat is flowing from the hot/warm portion of the engine to the cool/cold end. When you transfer to a block of ice the heat flow in the engine is reversed and the engine runs backwards.
Take note that the piston and displacer are approx. 90 deg out of phase which results in the engine running in the opposite direction.
In normal operation heat is flowing from the hot/warm portion of the engine to the cool/cold end. When you transfer to a block of ice the heat flow in the engine is reversed and the engine runs backwards.
Take note that the piston and displacer are approx. 90 deg out of phase which results in the engine running in the opposite direction.
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scottthomas
- Posts: 4
- Joined: Sat Sep 10, 2005 9:37 pm
- First Name: Scott
- Last Name: Thomas
Response to Heat runs one way, cold the other....im confused
A Stirling engine runs off of air pressure acting on the power piston. Heat merely provides the means of creating pressure. It is easier to visualize if you have access to a low temperature Stirling with a transparent displacer cylinder. When the displacer moves to the cold end of the cylinder the air contacts the hot surface in the cylinder and expands creating pressure. This pressure pushes on the power piston creating work. As the power piston travels out due to the pressure, the displacer begins to move toward the cold end of the cylinder. When the air contacts the cold surface it contracts reducing pressure on the inside and allowing atmospheric pressure on the outside to push the power piston back in.
The displacer is attached to the power piston such that it is 90 degrees out of phase with it. This arrangement provides the optimal timing of air movement between hot and cold to act on the power piston. This also makes the engine directional.
When you set the engine on ice instead of heat you are reversing the hot and cold ends of the motor. The hot end is now at room temperature and the cold end is at ice temperature. Whereas when you started the room temperature end was the cold side. This is why it changed directions.
Does this help?
The displacer is attached to the power piston such that it is 90 degrees out of phase with it. This arrangement provides the optimal timing of air movement between hot and cold to act on the power piston. This also makes the engine directional.
When you set the engine on ice instead of heat you are reversing the hot and cold ends of the motor. The hot end is now at room temperature and the cold end is at ice temperature. Whereas when you started the room temperature end was the cold side. This is why it changed directions.
Does this help?