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I have a new fluid, called Unobtaniol, which is a room temperature frictionless superfluid. It has the same physical properties as liquid helium, but with less freezing everything.

A friend of mine reckons that it would be great for lubricating gears, pistons, various forms of reciprocating arm, worm assemblies, you name it. I'm not so sure.

Would this fluid be a good lubricant, and if not, why not?

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    $\begingroup$ It might make a better hydraulic fluid; those systems are contained and tightly sealed. $\endgroup$
    – Amadeus
    Aug 9 '17 at 15:06
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    $\begingroup$ If it's frictionless it will flow out of bearings and you'll be left with no lube at all. $\endgroup$
    – Hot Licks
    Aug 9 '17 at 23:34
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    $\begingroup$ @HotLicks Er, i must disagree: you describe, moreso, something with no surface tension. $\endgroup$ Aug 10 '17 at 2:10
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We don't aim for lowest friction in lubricants. We aim for appropriate friction.

Viscosity or thickness of the lubricant is significant in all uses. We don't always aim for the lightest possible oil, often what's used is a much heavier grease. The choice of grease is appropriate to the load and coarseness of the materials involved.

A delicate mechanism would require a very light oil with a very low viscosity. A heavy duty piston or axle bearing often requires a heavy grease, this is to ensure that gaps are filled and the grease adheres to rougher surfaces to act as a lubricant. A very light oil would not adhere in a thick enough layer to allow for the roughness of the surfaces involved.

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    $\begingroup$ Also superfluids climb on all the surfaces. You don't want the oil of your engine to crawl into the combustion chamber and from there to the exaust. $\endgroup$
    – L.Dutch
    Aug 9 '17 at 16:38
  • $\begingroup$ Can we smooth out the surfaces of the heavy duty piston or axle bearing to the point a lighter oil can be used without being too thin? $\endgroup$ Aug 10 '17 at 6:58
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    $\begingroup$ @JohnDvorak, often you can but the cost goes up, and for what you gain it's not cost effective. $\endgroup$
    – Separatrix
    Aug 10 '17 at 7:04
  • $\begingroup$ @L.Dutch Notice that oil gets sprayed onto the cylinder walls and sometimes pistons from below. It's not (just) gravity which keeps the oil in the engine, hence the ability to climb does not preclude a liquid from being used in an engine. $\endgroup$
    – JimmyB
    Aug 10 '17 at 11:44
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    $\begingroup$ @JimmyB It does make it extremely hard to contain. I'm not even sure if you could design an enclosure that it couldn't escape from, especially considering you need some method to replace the oil. $\endgroup$
    – JMac
    Aug 10 '17 at 12:07
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Just to clarify: a "frictionless" fluid would have no tendency to coat surfaces - it would "slip" right off. That means a sandwich with it between two surfaces would not protect the two surfaces from one another.

Making the frictionless substance bondable may make it work:

So consider this the cross-sectional situation between two surfaces A & B with a lubricant,L: -A-A-L-L-L-B-B-. If L is both frictionless AND bonds well to both A and B AND the A-L and L-B also don't interact with L, then you might have a damn good thin film lubricant. (Of course, lubricants have a lot of properties in addition to their modifying the coefficient of friction which determines if they'd be useful or not.)

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  • $\begingroup$ This does not provide an answer to the question. Once you have sufficient reputation you will be able to comment on any post; instead, provide answers that don't require clarification from the asker. - From Review $\endgroup$
    – L.Dutch
    Aug 9 '17 at 18:22
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    $\begingroup$ @L.Dutch, I disagree. His first two sentences directly answer the question. The remains of his answer suggest a modification that would make it useful. I'll edit the formatting to make it more clear. $\endgroup$
    – ShadoCat
    Aug 9 '17 at 18:36
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    $\begingroup$ This is actually an exceptional answer, and solves the problem I was having with this concept. Thank you!! $\endgroup$
    – Joe Bloggs
    Aug 10 '17 at 8:41
  • $\begingroup$ Not entirely true, especially when specifying "same properties as liquid helium". Helium flows in a thin film that coats ALL surfaces, and will in fact escape from any open container by creeping over the sides via this film. Unfortunately I cannot find any studies that have actually been done to see how much a helium film reduces friction between two surfaces. $\endgroup$
    – Skyler
    Aug 10 '17 at 14:16
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I'd say no, unless you suspend the machinery in it. Frictionless sounds like it would be great until the moment you put it on something and it slips off. I don't know that much about the physical properties of liquid helium, but I'm guessing it's not very viscous, so it would not tend to stay put.

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    $\begingroup$ What makes a superfluid a superfluid is 0 viscosity. $\endgroup$
    – JMac
    Aug 10 '17 at 12:10
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It could be used in pressurized fluid bearings essentially creating an absolutely frictionless bearing. It could NOT be used in non-pressurized non-sealed scenarios because, as stated before it would not stay on.

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I don't think it could BE a liquid without friction. The fact that it has friction allows it to fill a volume. No friction would mean it floats. Maybe minimum friction? But even then it isn't likely to be very useful unless you're trying to keep apart two objects that have very little mass or force and don't want them to be overwhelmed because they're super delicate. Motor oil is super viscous because it's used to keep very dense, heavy objects apart. It definitely has friction though because it sticks to everything.

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  • $\begingroup$ Helium becomes a superfluid when you drop the temperature extremely low (within degrees of absolute zero). Superfluid helium has no friction and zero viscosity, and friction and volume are not actually related. I don't quite understand the physics of how superfluids form and act, but you can read a bit about them here $\endgroup$ Aug 11 '17 at 6:41

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