Comments on: Self Propelled Liquid Droplets

Self Propelled Liquid Droplets

dhruva — Thu, 06 Apr 2006 00:57:25 -0800

Self Propelled Liquid Droplets : When a liquid drop is placed (.mov files) on a surface held at a temperature much higher than the liquid's boiling point it hovers on its own vapor cushion, without wetting the surface.

By: matteo

matteo — Thu, 06 Apr 2006 01:57:44 -0800

that's how you walk on hot coals right?

By: cadastral

cadastral — Thu, 06 Apr 2006 02:01:23 -0800

very cool... thanks for this.

By: dhruva

dhruva — Thu, 06 Apr 2006 02:05:55 -0800

that's how you walk on hot coals right? Related Mefi post.

By: 2sheets

2sheets — Thu, 06 Apr 2006 02:25:00 -0800

The effect can be achieved with a wok or iron skillet. it's especially fun with a wok.

By: insomnus

insomnus — Thu, 06 Apr 2006 02:25:14 -0800

Easy to do in your own home by just heating up a stove plate and dropping some water on it.

By: vacapinta

vacapinta — Thu, 06 Apr 2006 02:41:46 -0800

I think people are missing the point of the post. Yes, you can do this on a skillet. But, if you see that last link you'll see that the real discovery here is that these droplets can be made to move uphill!

By: furtive

furtive — Thu, 06 Apr 2006 04:03:59 -0800

I was under the impression the hovercrafts slid down hills and that's why you only see them on relatively horizontal surfaces such as water. N'est pas?

By: quonsar

quonsar — Thu, 06 Apr 2006 04:26:14 -0800

i have eels in my hovercraft.

By: bouncebounce

bouncebounce — Thu, 06 Apr 2006 04:40:55 -0800

I don't care about your hovercraft, quonsar, I'm too busy trying to get these scratches off my tobbaconist's.

By: loquacious

loquacious — Thu, 06 Apr 2006 04:46:14 -0800

I never realized quonsar's pants were in effect a ground effect vehicle. These droplets roll uphill - when said inclined plane is sawtoothed or ratcheted and is significantly warmer then the droplet of liquid placed upon it. So, plain water on a sawtoothed, sufficiently hot metal plate will "defy gravity" by rolling uphill against the grain of the sawtooth due to the way the steam vapors escape differently from the droplet, depending on where on the sawtooth the droplet is. Same goes for very cold liquid nitrogen on a much warmer yet room-temperature sawtoothed plate. This isn't just a droplet skittering around a hot griddle. It's a counterintuitive discovery that could actually lead to some useful things. Say, a pumpless water cooled engine, or methods of cooling chips in computers without resorting to moving parts or exotic materials, or utilizing waste heat to pump or manipulate liquids. Note that in the videos they also use a channel with sawtoothed walls, and large water droplets zip through it like they were shot out of a gun. A channel is practically a tube - just one wall short, so it'd be logical to assume that tubes might also work as well.

By: hypersloth

hypersloth — Thu, 06 Apr 2006 05:03:10 -0800

wonderful link, thanks.

By: The Boy

The Boy — Thu, 06 Apr 2006 05:48:41 -0800

that's cool in the first slowmotion video the water looks like a slinky

By: solotoro

solotoro — Thu, 06 Apr 2006 06:24:06 -0800

It's not REALLY self-propelled, as you're applying energy from the plate, but it is still very nifty. Perhaps, PERHAPS, even niftier than putting liquid nitrogen in your mouth (which is safe due to the same effect - but don't swallow it!).

By: NewBornHippy

NewBornHippy — Thu, 06 Apr 2006 06:42:25 -0800

I'm so hot -- that why shower never work for me.

By: Farengast

Farengast — Thu, 06 Apr 2006 07:27:52 -0800

Perhaps, PERHAPS, even niftier than putting liquid nitrogen in your mouth (which is safe due to the same effect - but don't swallow it!). Yeah, it's safe as long as your mouth is dry. If your mouth is too wet then the water will flash freeze and crack a tooth.

By: horsewithnoname

horsewithnoname — Thu, 06 Apr 2006 07:52:54 -0800

Very cool mechanism. But I don't see how using this phenomenon adds anything to a micropump. Aren't we still relying on steam to get to the condenser?

By: rosemere

rosemere — Thu, 06 Apr 2006 07:59:57 -0800

The Leidenfrost effect is neat, but I doubt that it contributes much to successful fire-walking. You don't see any sane people walking on very hot cast iron, where the LE should work as well as anywhere else. Firewalking occurs on coals of various sorts. The explanation I've heard is that the coals are at a high temperature, but actually retain relatively little heat because they're so porous. (Think: sticking your hand into the hot air of a 400 degree oven; touching a potato baking at 400 degrees; touching an oven rack at 400 degrees.) It's also a good idea to walk briskly and forget about dawdling on the coals. The experience is supposed to be like walking on hot beach sand, although it can subjectively feel cooler if you do those New Age chants and crap before and you really psych yourself into thinking they'll have an effect. The link? Water roling uphill is awesome.

By: weapons-grade pandemonium

weapons-grade pandemonium — Thu, 06 Apr 2006 08:15:02 -0800

The droplets aren't really rolling uphill. They are making small random movements in a rachet-like topology that prevents reversion, much like the Bush administration going up the creek.

By: OverlappingElvis

OverlappingElvis — Thu, 06 Apr 2006 09:27:47 -0800

Oooh... the glitter is really pretty. I always kinda wondered how water skated along hot surfaces (as in cooking).

By: wumpus

wumpus — Thu, 06 Apr 2006 10:50:29 -0800

If liquid gets out of laptops as easily it can accidentally get in, i'm not sure i want mine filled with near-vaporizing temperature liquids.

By: Alex404

Alex404 — Thu, 06 Apr 2006 10:51:24 -0800

i have eels in my hovercraft. Eels on a hovercraft, man. Eels on a motherfuckin' hovercraft.

By: jamjam

jamjam — Thu, 06 Apr 2006 15:17:18 -0800

I hesitate to substitute my own judgement for a professor's of physics and all his students', but if you look at the slow motion movie they provide, I think you can see that their explanation for the uphill motion of the drop is wrong. Instead of being pulled along by viscous forces acting at the base as they suggest, it's clear to me that, as the droplet passes over the deepest part of the ratchet, a sudden large jet of vapor escapes behind the droplet, which generates a quite large wave in the body of the droplet. This wave, in turn, moves up over the top of the droplet to the right, shifting the center of gravity of the droplet in that direction, and, by virtue of the wave's momentum as well, carrying the rest of the droplet along with it.

By: JHarris

JHarris — Thu, 06 Apr 2006 15:44:45 -0800

That's a strange definition of "safe" you have there, Farengast. I imagine a lot could go wrong, I'd rather not tempt the Physics Gremlins like that.

By: Ynoxas

Ynoxas — Thu, 06 Apr 2006 19:55:42 -0800

Eels on a motherfuckin' hovercraft. posted by Alex404 at 12:51 PM CST on April 6 [!] No, no, no. *ahem* I want these motherfucking eels off this motherfucking hovercraft!