superfluid fountain effect
/ SOO-per-FLOO-id FOWN-tun ih-FEKT /
Hold a tiny tube of superfluid helium, shine a faint light on its base to warm it ever so slightly, and the liquid leaps up the tube and squirts out the top like a little fountain. Warming a liquid to make it shoot upward sounds backwards — heat usually just makes things bubble or steam — yet a superfluid does exactly this.
The fountain effect happens because, in a superfluid, heat and flow are strangely linked. Picture the liquid as a normal, heat-carrying part plus a frictionless superfluid part. If you pack a narrow channel with fine powder so only the frictionless part can squeeze through, then gently heat one side, the superfluid rushes toward the warm region to try to even out the temperature — and because that frictionless flow meets no resistance, it can pile up enough to spurt out of a nozzle in a steady jet.
It matters as one of the most vivid, hands-on demonstrations that a superfluid is governed by quantum rules, not by the ordinary push-and-shove of pressure. The common misconception is that the heat is boiling the liquid upward; nothing is boiling at all — the jet is driven by the superfluid component flowing toward heat, a purely mechanical response to a temperature difference.
In the classic demonstration, a glass tube packed with fine emery powder dips into superfluid helium; the faintest heating of the powder sends a thin jet of helium spraying several centimeters into the air, kept going as long as the gentle warmth lasts.
A whisper of heat sends superfluid helium jetting out of a powder-packed tube.
Because only the superfluid part can pass the powder plug and it carries no heat, the liquid arriving on the warm side is even colder than where it came from — the fountain effect can actually be used as a tiny heat pump.