MadSci Network: Physics

Re: Why does supercooled helium run uphill?

Date: Wed Feb 25 11:30:27 1998
Posted By: Jay H. Hartley, Post-doctoral physicist, Lawrence Livermore National Lab
Area of science: Physics
ID: 887135944.Ph

Strictly speaking, supercooled helium does not "run uphill," but it can under certain circumstances climb walls in apparent defiance of gravity. When helium, which turns liquid at about 4.2 degrees Kelvin (-269 C), is cooled further to below about 2 Kelvin, it undergoes a remarkable transformation. This phase of helium, referred to as Helium II, becomes superfluid. What this means is that the liquid's viscosity (the measure of its "stickiness") becomes nearly zero. At the same time, its thermal conductivity (it's ability to transfer heat) becomes almost infinite.

Because the viscosity is almost zero, the fluid flows very easily as a result of the smallest pressure or change in temperature. The response is so strong that such small forces will help the light-weight liquid climb against the force of gravity. A thin film of the liquid flows over and coats all the surfaces of its container. This film may only be a few millionths of a centimeter thick. If you have superfluid helium both inside and outside of a container, the fluid will flow through this thin film until the fluid levels and temperatures are the same inside and out, even if the rim of the container is much higher than the fluid level. In this sense it "flows uphill," because it will basically climb the wall of the container.

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