Bang But No Splash

BishopBerkeley writes "When a drop of ethanol is dropped on a surface at low pressures (1/5 atmosphere or less), it makes no splash. Science offers a brief synopsis and fascinating pictures of the phenomenon. The results seem to confirm the (perhaps counterintuitive) prediction that more viscous liquids are more likely to splash, not less likely . Links to the researchers' home page at U of Chicago (as of now, the site is timing out) and pdf version of the article on arxiv can be found on the Science page also."

Synopsis:

[martensitic]

I do not have access to this item.

Fascinating. ----- Ut Tensio, Sic Vis

Nice!

[Anonymous Coward]

Your Free Registration does not grant access to this item:
Full Text : Cho,Sucking Away the Splatter, ScienceNOW 2005: 4

Re:Synopsis:

[Neophytus]

The PDF has the pictures [nyud.net]. I wish people wouldn't link redundant urls.

An accessible page, more types of fluids tested

[ylikone]

Click here [uchicago.edu] to see.

ScienceNOW text

[Anonymous Coward]

Sucking Away the Splatter

LOS ANGELES--Nature may abhor a vacuum, but a vacuum abhors a mess. In the absence of air, a droplet of liquid can crash into a smooth surface without splattering, physicists report. The odd phenomenon might be useful for controlling droplet formation in technological processes like inkjet printing.

Splashdown. A drop of ethanol hits a smooth glass at atmospheric pressure (above) and 1/5 atmospheric pressure (below).
CREDIT: Lei Xu et al./The University of Chicago

It seems obvious and inevitable that a fast-moving droplet will splatter when it hits a hard surface. Researchers have studied the distribution of droplet sizes and energies in such splashes, and physicists Lei Xu, Sidney Nagel, and colleagues at the University of Chicago were searching for ways to control those sizes and energies when they discovered something unexpected: By pumping away some of the surrounding air they could eliminate the splatter entirely.
Within a tall vacuum chamber, the researchers released droplets of alcohol onto a dry glass plate from heights ranging from 20 centimeters to 3 meters. They recorded the resulting splashes with a high speed video camera as they varied the pressure in their apparatus, sucking it down as low as one hundredth of atmospheric pressure. The droplets struck the surface with speeds ranging from 2 to 7 meters per second, and for a given speed, the researchers found they could eliminate the splash by lowering the pressure beyond a specific threshold.

The team explains the results with a simple theory. As a drop strikes a surface, liquid begins to spread sideways at supersonic speed, creating a shockwave. The shockwave pushes back on the liquid, and if that force is greater than the internal forces holding the drop together, the shockwave will lift the liquid off the surface and create a splash. Reducing the pressure reduces the force exerted by the shock wave.

Ironically, the theory predicts that a thicker liquid should splash more than a thinner one. The researchers tested this curious prediction by studying the splash made by three types of alcohol with different viscosities. Indeed, the more viscous the alcohol, the lower the pressure needed to prevent splashing, the team reported here this week at a meeting of the American Physical Society.

"It's not uncommon to see a lovely phenomenon, but it is uncommon to get all the factors straight," says Walter Goldburg, an experimenter at the University of Pittsburgh in Pennsylvania. Bulbul Chakraborty, a theoretical physicist at Brandeis University in Waltham, Massachusetts, says the researchers' analysis opens the way to controlling splashing in, for example, spray coating surfaces with various substances.

Re:An accessible page, more types of fluids tested

[andy753421]

For everyone without real player just change the *.splash.rm to *.splash.avi [uchicago.edu] on the video link since even the 'AVI format' link points to a real media file.
The movie seems to me much more effective than the jpg image, I was supprised by them skipping head so far between the 3rd and 4th frame, seems leaves out some of the important parts..

LESS viscous liquids are more likely to splash

[Dikeman]

The posting says:
"The results seem to confirm the (perhaps counterintuitive) prediction that more viscous liquids are more likely to splash, not less likely"

While the article says:
"Xu tested water splash as well. Water exhibits the same behavior, but its higher surface tension narrows the range of splash-forming impact velocity and creates a much larger margin for experimental error.
"It's much harder to splash than ethanol," he said."

Is say, this is a classic RTFA

Re:An accessible page, more types of fluids tested

[shockbeton]

The link to the AVI is erroneous on the parent's linked-to page. It should be:

http://www-news.uchicago.edu/releases/05/050322.sp lash.avi [uchicago.edu]

A marvelous movie!

Re:How would superfluids behave?

[MustardMan]

To follow up on your follow-up, water is hard to splash because it's a polar molecule. There's a slight positive charge off to one side and a slight negative charge off to the other. Hence, the molecules of water tend to attract each other. They also attract lots of other stuff, which is why water is so great as a solvent, why you get a meniscus at the top of a test tube, why rain droplets form nice round bubbles on the surface of your car, etcetera.

Sometimes in science I tend to get caught up with the complex math and theory, and forget the basic stuff. Water is a truly fascinating material, and can give us a lot of insight into the workings of the world.

Re:LESS viscous liquids are more likely to splash

[Herbster]

uh. surface tension and viscosity are NOT the same thing.

Air pressure is critical

[jbeaupre]

This was discussed in Science News (or maybe elsewhere) some time back so I'm working from memory. One of the things reseachers noted was that air was crucial for splashing. It's rather intuitive in a way. All of the momentum is downward, then converted to radially outward. What makes it go up? The leading edge of the droplet is rushing outward. With the right speed and gas pressure, it splashes up like popping the hood of your car while going down the highway. Get rid of the speed or the gas and it will stay low.

More beer research ...

[mikael]

You might also want to read the following papers:

A Comparison Analysis of the Greater Carbohydrate and Increased Photosynthetic Element Count of Budweiser Versus the Similar Enzyme Content of Bud Light [msu.edu]

Next to medicine and biowarfare, brewing and fermentation technology [byo.com] is a major funding source for microbiology.

Some research suggests that drinking beer may stop your hair from turning grey [japancorp.net]

And possibly the most expensive PDF's in the world [just-drinks.com]

Re:How would superfluids behave?

[Anonymous Coward]

Ethanol is a polar molecule aswell, not as polar as water though.

Keyword: multiphase flows, fluid-fluid interaction

[xlurker]

What would be great is to check this phenomenon out with computer simulation.

That's exactly the first thing I thought of. And this begs to be simulated.

It might be tough to set up though, since you'd have to deal with a compressible gas phase and incompressible fluid phase, and keep track of the fluid surface to account for surface tension.

You pretty much described what is done. The Navier-Stokes equations for compresible and incompressible fluids are used. But in this case air-compression is so low, that incompressiblity could be assumed. All of the difficulty here is tracking the surface and maintaining surface tension. From the equations you can read that the surface tension will depend on two things: pressure jump and the jump of the normal derivative of the fluid velocity. Possibly an artificial surface tension could be added that depended on the change of curvature of the interface surface.

I'm sure it could be done though. Axisymmetric simulation would probably be fine to start off.

Only recently, the preferred approach to date uses a method called the level set method. Here the interface is explcitly tracked. Problems arise here because originally the numerical methods and underlying mathematics that are used weren't set up for changing domains i.e. changing differential equations in the middle of a discrete spacial cell in (a finite element).

further research

[emilng]

I was curious enough about what you said to do some further research. I found the following:

Protein denatures as you beat it up with the whisk Fat globules are dispersed into smaller and smaller droplets as well,,,hey, how would you like to be whipped with sharp slicing pieces of metal?????? All the while, water is swirling and moving creating eddies of air like a sunami in your bowl Sugar is looking for a safe place to land in all the confusion.... End Result: Uncoiled protein (denaturation) surrounds the air bubbles Sugar lands on the denatured protein and holds on for dear life Fat surrounds the sugar, protein and air bubble, trapping the water Now multiply this scene by about 2 zillion K-billion times You have created an interlaced 3-dimesnional net we call a foam (remember our dispersion chart???? Foam is a gas dispersed in a liquid.....air trapped in milk)

So you wouldn't be able to get the milk to turn into whipped cream which turns into butter without the air for the fat, protein, and sugar to cling to. So this is why the milk is shipped in a vacuum.

Full text: http://www2.muw.edu/~jfitzger/page81.html [muw.edu]

Axisymmetric simulation NOT correct

[elgatozorbas]

Axisymmetric simulation would probably be fine to start off.

Wrong

Strange enough, axisymmetric simulation would probably of little use. Falling drops are one of those phenomena where a completely (or almost completely) symmetrical initial condition leads to a very asymmetrical result. In practice you do not get a circular 'wall' of fluid, but rather a kind of 'crown'. (Google came up with this example [casburt.com]). The number of peaks of the crown has been investigated by someone, but I have forgotten who. More about symmetrical conditions leading to asymmetrical results can be found in the book Fearful symmetry [amazon.com].

From TFA...

[Otto]

"In an engine you break the gasoline into millions of pieces and then ignite them in a chamber, making a controlled explosion. You do that continuously in your car," Xu said. "A higher gas pressure might do a better job of breaking the fuel into smaller, more uniform pieces. But determining that would require further experiments more accurately simulating the splash process as it occurs under fuel-combustion conditions," he said.

Re:Air pressure is critical

[jbeaupre]

Hey, don't shoot the messenger. I'm just telling you what I remember from the article. As for elastic collision, liquids have no elasticity in the way you are suggesting. Bouncing comes from bulk compression. Fluids, well, flow unless constrained. A droplet isn't constrained so it splats. Except for a miniscule shock propagation wave, you won't get KE->PE->KE of a bounce. But your point about it splashing over itself is a good observation. Sort of creating its own pool then splashing it out. I wonder if they considered it. I apologize for the word intuitive. It's a subjective term.

Re:Distorted Shape

[Jozer99]

That was caused by air resistance. A drop falling in pressure such as the atmosphere gets destorted, that is why raindrops have that famous teardrop shape. In the lower pressures, the effect is much less.

Re:As Dave Barry pointed out....

[Flavio]

A nuclear bomb can be detonated by taking two lumps of metal and banging them together real fast. The romans could have done that, easily.

That's ridiculous. Your two lumps of metal are highly enriched uranium or plutonium, neither of which occur naturally. The process to obtain them in sufficient quantities requires huge amounts of energy, raw materials and precision engineering.

So no, the Romans couldn't have done that, and specially not easily.

Re:An accessible page, more types of fluids tested

[FatBear]

That's what it looks like as it leaves the spigot, but it quickly assumes a spherical shape as it falls. Surface tension pulls the same on all surfaces of the drop, so it would pull it into a sphere. In a vacuum it should attain a perfect sphere, though it may take some time because of sloshing around inside the drop. Atmospheric drag would tend to flatten the bottom of the drop as it falls. If you look at the film clip (see previous posting) you will see that the drop falling through the denser atmosphere is noticeably flattened, while the drop falling through the thinner atmosphere is more spherical.

putty is a very bad example

[bodrell]

Because it's a non-Newtonian fluid [wikipedia.org]. More specifically, it's a Bingham plastic. [wikipedia.org] I wouldn't expect any non-Newtonian fluid to behave in a "normal" way. They don't flow like water (plug flow, rather than laminar) and have very funky properties, in general. It's complicated to discuss viscosity of a Bingham plastic, but I think ketchup is another example.

A Natural Fission Reactor

[duffahtolla]

I doubt that story too, but I remembered reading about nature achieving a self sustaining reaction on its own.

From here [teachnet.ie]

A Natural Fission Reactor For thirty years it was assumed that the first nuclear chain reaction to occur on Earth was that set up by Fermi in Chicago in 1942. However, it has now been established that a natural reactor operated in a natural uranium deposit in west Africa 1.8 billion years ago. Evidence for this came in an interesting way. Natural uranium from Gabon was exported to France; an examination of the isotopic content showed that the proportion of uranium-235 was slightly lower than normally found This small difference was investigated and traces of the fission products of uranium were found in higher proportions than in normal uranium ore. This suggested that at some time in the geological history of the uranium, some of it had undergone a fission reaction. But how could a chain reaction have been established in natural uranium? The seam of ore, which was being extracted, was unusually rich in uranium-235 (up to 10 per cent). Geological conditions were responsible for accumulating large quantities in a small area. The water of crystallisation of the minerals in the ore might have acted as a moderator. It is now believed that a natural fission chain reaction must have taken place in the ore approximately 1800 million years ago. It may have run for just over 100 years, emitting a thermal power of tens of kilowatts (any greater power would have led to the evaporation of the water required as a moderator). In the course of its lifetime, it would have consumed a similar amount of uranium as a present-day power reactor consumes in a year.

Re:Does this apply to other situations?

[Anonymous Coward]

I had this same question a while back, and so I posed it to google answers. Consensus seems to be that it would be spherical. Check out http://answers.google.com/answers/threadview?id=16 9920 [google.com] for more info.

- jw

Re:Distorted Shape

[synaptik]

That was caused by air resistance. A drop falling in pressure such as the atmosphere gets destorted, that is why raindrops have that famous teardrop shape. In the lower pressures, the effect is much less.

Except that raindrops are not teardrop shaped. [fluidmech.net] Thanks for playing.

Re:Isopropyl Syringe Crack Mystery...

[Anonymous Coward]

My guess is the bubbles were from an existing thin crack leak, and you exacerbated it by playing with vaccuum.

If you heat glassware with no liquid, it gets hair-fine cracks in it, and will shatter if you touch the (apparently solid) body. Glass is an amorphous solid similar to plastics.