Motor Made From Liquid Film 241
KentuckyFC writes "Last year, a group of Iranian physicists made a puzzling discovery. They placed a thin film of water in a small cell and bathed it in two perpendicular electric fields. To their surprise this caused the water to rotate. They called their device a liquid film motor and posted on the web a cool set of movies showing the phenomenon. The puzzle is this: the electric fields are static, so what's driving the motor? Now another group of physicists has the answer: a complex interaction between the electric field, the cell container and the liquid causes water to move along the cell wall. Crucially, it moves in opposite directions on opposite sides of the cell and so sets up a circular flow. The phenomenon works only when friction and surface tension are significant forces so the effect is entirely scale dependent. That's probably why we haven't seen it before and also why it could have important implications for microfluidic devices such as lab-on-a-chip."
Re:Where does the energy come from ? (Score:5, Informative)
OK, having read the "real" article [arxiv.org], the best response is that this may explain the observed effects. The major differences
- the depth of the film is an important parameter, but that isn't known for the original experiments, so they can't compare results to theory in a detailed fashion.
- the theoretical work leads to at most one steady vortex in a container, but the experimental results show both one and two. The two vortex results may, of course, be transient.
- the theoretical results have flow speeds largest at the outer boundary. The experimental results have it increasing towards the center. This may be explainable by other effects, such as surface tension, but it is a discrepancy.
And the article says nothing directly about where the energy is coming from, but, reading it, it must be the electric field.
nope (Score:3, Informative)
"droog" is the Russian word for friend. Also, how come I can't enter UTF-8 chars in a slashdot post without them getting mangled?
Re:Where does the energy come from ? (Score:3, Informative)
Well, I don't see it in the pictures, but the original article [arxiv.org] does make this clear - one of the two electric fields is done by putting copper electrodes in the water, so a current is flowing and you are correct.
Video mirror here (Score:3, Informative)
http://www.youtube.com/watch?v=wxydLVodoxE [youtube.com]