Thursday, 12 November 2009

The teapot effect, end of

So apparently, there's something called the teapot effect. Or, rather, there was.

No, it's not what you might first imagine it is. At least, it's not what I first imaged it was. Instead, it's apparently the name used for the phenomenon whereby the spouts of teapots dribble, and even English women who've been pouring tea for posh friends for decades are unable to pour that perfect, immaculate cup of tea.

"Previous studies have shown that dribbling is the result of flow separation where the layer of fluid closest to the boundary becomes detached from it. When that happens, the fluid flows smoothly over the lip. But as the flow rate decreases, the boundary layer re-attaches to the surface causing dribbling."
And here's where fluid dynamicists have stepped up, donned their superhero cloaks, and sorted the problem. Huzzah!

The factors involved?

"Previous studies have shown that a number of factors effect this process such as the radius of curvature of the teapot lip, the speed of the flow and the "wettability" of the teapot material. But a full understanding of what's going on has so far eluded scientists.

"Now Cyril Duez at the University of Lyon in France and a few amis, have identified the single factor at the heart of the problem and shown how to tackle it. They say that the culprit is a "hydro-capillary" effect that keeps the liquid in contact with the material as it leaves the lip. The previously identified factors all determine the strength of this hydro-cappillary effect."

The solution is two-fold: make the lip of the teapot as thin as possible, and and coat it with superhydrophobic materials (materials, in other words, that really, really, really, really don't like water).

Even more fun, apparently there are materials in which the superhydrophobicity can be turned on and off electronically. Meaning that to dribble or not to dribble would no longer be hypothetical...

And, because there's no better way to end things than with wry, physics-based sarcasm, there was this comment, as well:
"(Of course, there are one or two other potential applications in shaping the fluid flow in microfluidic machines but these pale into insignificance compared with the teapot revolution in hand.)"

On another teapot-related note, I had not idea, but apparently teapot-blowing (again, not what you think) is something of an artform!

p.s. Yes, I know the original arXiv post isn't that new - sadly, life has perforce distracted me somewhat of recent.


guy said...

Now - if only they can fix those damned milk jugs, too! They've always been far messier than teh teapot.

Suspect it's not quite as simple, as they are not closed spouts...

aimee said...

dunno. no mentioned was made in particular that the spout had to be closed - it seems simply a matter of curvature, thin and superhydrophobic material...
then again, no idea :)
(ooh, also, not sure if you know, but here's my blog on Sciblogs: