Ferrofluid Piston

A good application for ferrofluid is to seal the cylinder of a Stirling motor. The piston shall seal the cylinder and it shall run with low friction. Achieving both targets requires some precision

It becomes simple when thin magnetic oil, stays attached to a magnetic piston. Forming an elastic sphere around the magnet, the oil closes the gap. The piston is even centered in the cylinder.

For demonstration the working cylinder is extended with a displacement cylinder to a Stirling motor. For the operation some heat is applied to the left side of the displacement cylinder, while the right side remains cold.

When it gets warm inside, the air expands and the working cyliner pushes its piston out. The pingpongballs roll from the cold side to the warm displacing the air to the cold side. This leads o a contraction of the air and the working piston and the balls return for the next cycle.

A high position of the barycenter of the displacement cylinder relative to its suspension provides some hysteresis to the system so that it cycles without a flywheel.




Ferrofluid Kolbendichtung

Eine gute Anwendung für Ferrofluid ist das Abdichten des Zylinders eines Stirlingmotors. Der Kolben soll den Zylinder gut abschließen und sich dabei reibungsarm bewegen. Beide Ziele sind oft nur mit hoher Präzision in der Ausführung zu erreichen.

Mit dem Einsatz von Öl, das magnetisch am Kolben haftet, wird es dagegen sehr einfach. Mit einem kugelförmigen Öltropfen der vom Zylinder in die Form gepresst wird, wird der Spalt geschossen und der Kolben wird dabei sogar noch im Zylinder zentriert.

Zur Demonstration wurde der Arbeits-Zylinder mit einem Verdränger-Zylinder zu einem einfachen Stirlingmotor erweitert.

Zum Betrieb wird die linke Seite des Verdrängerdzylinders erwärmt während die rechte Seite kühl bleibt. Bei der Erwärmung dehnt sich die Luft aus und drückt den Kolben des Arbeitszylinders heraus.

Durch die Veränderung der Lage rollen die Tischtennisbälle von der kalten zur warmen Seite und drängen dabei die Luft zur kalten Seite. Die Luft zieht sich zusammen, der Kolben und die Bälle gehen zurück und es beginnt der nächst Zyklus.

Eine hohe Position des Schwerpunkts Verdrängerzylinders bezüglich seiner Aufhängung führt zu einer Hysterese, die auch ohne Schwungrad eine zyklische Bewegung ermöglicht.

Category:

Science & Technology

Tags:

• Ferrofluid
• Piston
• Stirling
• Motor
• Nano
• Technology
• Physics
• Experiment

[shaytan1313]

could you tell me how much compression a piston ov that size is capable ov producing without breaking the ferro seal? i assume you used a neodymium magnet as that would probably be a main factor (magnetic stregnth) but i was just curious as to the pressures that can be obtained before the ferrofluid weakens.. do they manufacture diffrent fluids with diffrent iron concentrations?

[manf1234]

@shaytan1313 The limit of pressure for the construction shown here was 200 HPa (0.2 atm). You can extend it with smaller clearance (also with multistage and with condensed fluid). With a very small clearance in the end the pressure is not limited by the magnetic effect.

[specallez]

Brilliant! Could you tell me if you used a particular kind of ferrofluid ? You said "light oil", is there a particular one I should buy ? Also, what was the clearance between the magnet and the cylinder ?I'm going to try this in a an engine, thanks for sharing!

[manf1234]

@specallez All normal commercial ferrofluid will fit. The clearence in this case was about 1mm, or a little more. Smaller values are better for more compression. Keep the oil away from hot engine parts.

[pali52]

Thank You the idea, I tried ferrofluid with some machines You see in videos. 100 % seal, no friction. Please advice, how can I use in high pressure.

[manf1234]

Yes, I have seen your engines with pleasure.

A narrow gap and a multiple seal increases the available pressure.

It depends on what pressure you need. It might not be much more than one atmosphere in the end.

[ChuckRoveg]

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[codzomz]

well a real app. would not be possible or would be very hard to get this to work, because you would need to posses a magnet strong enough that the ferro fluid would maintain its shape during the compression cycle, also ferro fluid can ignite with a great enough heat application, so you would have to watch out for pre-ignition or combustion, also ignited air could escape into the crankcase which would cause some serious combustion issues, just too many variables to this theory, great idea tho:)

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[Razorlol69]

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[xolan007]

This is the principe of the stirling engine, right?

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