I am wondering whether and how superfluids (possibly at room-temperature, if that is possible at some point) can be of any practical use in mechanical or electrical engineering or other fields.

I would be delighted if you could provide me with some thoughts about hypothetical or even practical (at low temperatures) realizations of machines that use superfluids and might have a huge impact.

  • $\begingroup$ I am note sure if i got your question...are you interested in applications like: Cooling of superconducting magnets? Those are used in fusion reactors or magnetic resonance imaging. $\endgroup$ – rul30 Sep 6 '15 at 8:44
  • $\begingroup$ Well not quite, my interest is more whether we can make machines waste less energy due to a lower friction and how such things can get realized. $\endgroup$ – tobias Sep 6 '15 at 10:30
  • $\begingroup$ But it is the low friction of the supercooled helium which enables the cooling of the coils. So the low friction character is exploited. Or are you looking for more turbomachine-esque application? $\endgroup$ – rul30 Sep 6 '15 at 11:36
  • $\begingroup$ I am interested in any form of utilization of superfluids that has nothing to do with cool conditions or the quantum nature of superfuilds, but just with reducing friction. Also the motion that the superfluid is exposed to should be low, for instance as shear rate in a rheometer it should be around 0.04 s^-1 and ideally it should a more or less constant motion that is not getting altered much. $\endgroup$ – tobias Sep 6 '15 at 13:50
  • $\begingroup$ I think that this question is way too broad. Possible future uses for things that aren't really practical will just lead to speculation without any possible way to "answer" the question. $\endgroup$ – hazzey Sep 10 '15 at 23:04

Your comment, "my interest is more whether we can make machines waste less energy due to a lower friction and how such things can get realized" provoked me to respond:

On an initial thought, a fluid with no viscosity should be great because it means that there's no friction, right? I'm assuming this is your train of thought.

The flaw here is that there's no viscous friction - lubricants "want" a low viscosity because viscous friction causes the lubricant to heat and thus draws power from the system, but at the same time a lubricant needs viscosity because lubrication relies on thin films between the load-bearing surfaces to lubricate.

The viscosity of the lubricant is what keeps the lubricant from spraying/rushing out from between the load-bearing surfaces. In light load applications the lubricant is typically a very light, low viscosity oil, like WD-40.

As the design loads increase, the required viscosity of the lubricant increases. I don't know how much automotive experience you have, but there's a noticeable difference between engine oil and the gear oil in a manual transmission. As loading continues to increase thickeners begin to be added to the oil, producing grease.

So, back to your question, if you tried using a zero-viscosity fluid as a lubricant you would find that it would shoot out from between the parts to be lubricated as soon as you applied any load because there is no viscosity present to slow the fluid from leaving the joint.

  • $\begingroup$ Hi chuck, many thanks for your answer. However, I am insecure whether I understood everything correctly. Assume we can bring all components of a machine where there is friction, for instance some hinges, into a closed space where there is bath of that superfuid and these components, for instance hinges, are placed into that bath. Would that change something regarding your conclusions? $\endgroup$ – tobias Sep 10 '15 at 10:50
  • $\begingroup$ Probably not because anywhere the hinge was under an actual load the fluid would flow out of the joint. It's similar to the reasoning behind grease on the Wikipedia page, "Greases are applied to mechanisms that can only be lubricated infrequently and where a lubricating oil would not stay in position." It stays in place with a high viscosity. The lower the viscosity the less force it takes to push the lubricant out of the joint. $\endgroup$ – Chuck Sep 10 '15 at 11:41
  • $\begingroup$ I'm making an educated guess that, at zero viscosity, it would take effectively no force to push the fluid out from between the load bearing surfaces, regardless of how much fluid the joint is in. You might be able to make an argument that adhesion could form a boundary layer one molecule thick, but in all practical applications a joint is not polished to that fine of a surface finish for one molecule to help. $\endgroup$ – Chuck Sep 10 '15 at 11:44
  • $\begingroup$ Many thanks for your comments. Regarding the second assumption, you are definitely right, but if we manage to make that "containter" completely closed my guess would be that the fluid has to stay inside. Or am I wrong? But in any event, do you see any application for a superfluid at rather low velocities that does not make use of the quantum nature, but just the vanishing or extremely low viscosity? $\endgroup$ – tobias Sep 10 '15 at 12:15
  • $\begingroup$ I don't personally, except maybe in research - the study of turbulence would probably benefit from a zero-viscosity fluid, but all it takes is one person with one good idea to spawn an entire industry. Edison invented the light bulb, but you need a way to electrically connect them (light socket), and a way to turn them on and off (light switch), and maybe a way to connect a portable lamp (electric receptacle), etc. - most of Edison's inventions and patents were all around a few pieces of equipment - phonograph, light bulb, etc., but they spawned the music industry, electric utilities, etc. $\endgroup$ – Chuck Sep 10 '15 at 13:43

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