Interesting, water wont spash in a vaccum

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Interesting, water wont spash in a vacuum

HERE'S a Zen-like question. If a drop of liquid falls on a flat surface and there is no air around it, does it make a splash?

The answer, which may or may not help you reach nirvana, is no. "This was to us an incredibly surprising result," says Sidney Nagel of the University of Chicago in Illinois. "If you didn't have the air, you couldn't splash. This means you would never get splashing on the moon."

Nagel and fellow physicists Lei Xu and Wendy Zhang were trying to measure the energy of liquid droplets flying away from splashing drops of alcohol. To eliminate any effects of air, they carried out the experiment in a vacuum chamber, where they could reduce the pressure within the chamber from the standard atmospheric pressure of about 1 bar down to 10 millibars. The team found that the lower the air pressure, the less the liquid splattered. And the splash disappeared when the air pressure reached about 0.2 bar.
http://www.newscientist.com/channel/fundamentals/mg18624935.200

What could be some usefull implication with this?
 
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arildno

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I have no idea, but what a delightfully cool result!
Thank you very much.
 
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Perhaps the splash wasnt visible, but there was definitely some deformation like russ_watters is saying. It is an inelastic collision, in some form.
 

Integral

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I am not sure what they mean by "the splash disappeared"?

What happened to the drop? Did the drop adhere to the surface? Did it bounce off while maintaining the integrity of the droplet? Unfortunately the referenced article is pretty weak.

Isn't droplet formation the result of surface interaction between 2 fluids? So I am not surprised that removing air (one of the fluids) changes thing.

Come on Russ, think for a second, do you really believe that meteor impact on the surface of a planet is analogous to droplet formation in a fluid? I don't.
 

DaveC426913

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Integral said:
Come on Russ, think for a second, do you really believe that meteor impact on the surface of a planet is analogous to droplet formation in a fluid?
Of course it is.



I am curious as to what did happen in the experiment. The article seems to regard that as inconsequential.
 

Integral

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DaveC426913 said:
Of course it is.



I am curious as to what did happen in the experiment. The article seems to regard that as inconsequential.
Really? what is the surface tension of a planet?
 

Q_Goest

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At 70 F and 0.36 psia (0.025 bar absolute) water boils. So the 0.2 bar quoted is just above the saturation point of water.

Just guessing here, but I suspect the reason the splash "disappears" has something to do with it being so close to the boiling point. The article doesn't mention the temperature the drop was at. If it were as warm as 140 F, the water would have boiled.

Also I checked the surface tension, and stays roughly constant over that range.
 
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I should imagine a good use for this would be spot cooling or coating.

For example on small SMT devices, or precision engineering components where things need to be coated without contaminating other surrounding areas.

Again the question I'd ask is, so what did happen??? Bounced as a perfect globular shape, formed a perfect smeisphere on the point of impact?
 

Q_Goest

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Apparantly it has nothing to do with the boiling point of the fluid with respect to pressure. Here's a summary of another article referencing the same experiment.

University of Chicago physicists have learned how to eliminate what scientists formerly regarded as the inevitable splashing that occurs after a liquid crashes onto a flat surface. It turns out that the removal of air eliminates the splash process. ...

Xu’s path to discovery began with an experiment designed to study energy distribution in the many pieces that fly away from a breaking droplet. The experiment showed that after a droplet hits a flat, dry surface, it forms a thin layer that breaks into thousands of pieces. Xu then repeated the experiment in a vacuum chamber and lowered the air pressure. He and Nagel figured that the drag of the surrounding air might play some role in the break-up process.
“Once we lowered the pressure and did the experiment, it didn’t have any splash,” Xu said. ...

Researchers in the field previously had seen no reason for low atmospheric pressure to affect the results of their splash experiments. “There are many people working on this because it’s a very important technological area,” Zhang said. “Up until Lei’s experiment, the idea in the field of splashing is that of course the air doesn’t do anything, because it’s less dense and less viscous than water,” she said.

Instead, splash researchers generally focused on the interaction between the spreading droplet and the surface against which it collided. Their carefully controlled experiments produced reams of data but little understanding of the fundamental mechanism for splash formation.

“One of the things that is notorious in the splash-study community is that it’s very difficult to reproduce somebody else’s experiment. People have been working on this for more than a hundred years, and it is only recently that we understand enough about the different factors that affect the splash process to be able to reproduce results,” Zhang said.

The Chicago physicists isolated the effects of air pressure on splashing through a painstaking series of experiments involving four different gases and three different liquids. The gases selected—helium, air, krypton and sulfur hexafluoride—ranged from light to heavy. The fluids—methanol, ethanol and 2-propanol—have low surface tension, the force that makes a layer of liquid want to retract and form a droplet.

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.

Xu found that he could precisely control the amount of splash by tuning the pressure. The next step, he said, might be to investigate splash outcomes under experimental scenarios involving very large or very small drops, or drops traveling at higher velocities.
Ref: http://www-news.uchicago.edu/releases/05/050322.splash.shtml

What this is saying is that there are two factors which have a significant influence on the amount of splashing, surface tension and gas density. In general, it seems the lower the surface tension, the easier it is to get the liquid to splash. Second, the more dense the gas, the easier it is for the liquid to splash. So a liquid with a low surface tension impacting a solid surface in a high density gas will be the easiest to splash. In this case, I think "splash" might best be defined as the ability of the fluid to break up into droplets upon impact. If the liquid doesn't splash, it will simply wet the surface as is shown in the high speed still photos on the link above.

This is particularly interesting to me because it may directly relate to a phenomena regarding the transfer of liquid helium - something I have a professional interest in.
 
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This i believe can be related to pure logic.... Imagine this, a drop of water falls on the surface ~ elastic collision ~ the drop which was squished due to impact comes up, meet's surrounding air molecules and the water which is made of molecules of water or other smaller droplets of water itself ~ split up, some move up, some reflect back down to the ground and so on......

This naturally would depend on the density of the air moloecules as more the air molecules more the chances of the water droplet scattering....

And it would aslo depend on the surface tension as the greater the surface tension greater is the ability of the small water droplets to stick together and lower the surface tension lesser the the chance that the droplets of water will stay together....

what do u guyz think?
 

DaveC426913

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Integral said:
Really? what is the surface tension of a planet?
Actually, I'll correct myself. You said it's analagous. It's not merely an analogy, they operate on the same principles.

That's how you get secondary cratering, a central peak and many other features that both phenomena exhibit.
 

Clausius2

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I don't know what do you mean with splashing, but apart of surrounding air there is the gravitational force. I don't believe a drop falling in a liquid is not going to cause none effect no matter there is no air.
 

Integral

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This is not about cratering, that is why I say this is not analogous to meter impact. The analogy would be a model of the behavior of the METEOR, not the material that was in the crater. Note that at the energies observed here one surface can be considered infinite density and infinitely rigid. They are observing the behavior of a droplet. And a relatively low energy droplet at that. So please do not put this phenomena in the same box as high energy cratering collisions. Or even collisions between bodies of similar density.


Clearly if you impact a fluid surface in a vacuum there would still be material pushed aside. I think what this result implies is that the appearance of the splash would be much different form what we normally see. It implies that it would not segment into droplets in the same fashion. Droplets may well be due to viscous drag of the atmosphere. It would be very interesting to see video of such a splash.
 
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Could the no splash effect be due to the energy from the impact?
which causes any sort of "splash" to be instantly boiled off due to the pressure being so low?
 
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I think the reason we are use to seeing splashing is because as a drop falls through air it develops a depression on the underside looking much like an umbrella. This traps air when the drop hits the surface. Pressure increases for the air bubble and it accelerates up and out taking some water with it.

I wonder what dropping a cannon ball into a pool of water with no air would look like. Would we see some splashing then?
 
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Well, I don't see why not. They didn't drop a solid object into a fluid body. They dropped a fluid object onto a solid body.

Then again, maybe not. I can imagine it either way, I guess.
 

DaveC426913

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GOD__AM said:
I wonder what dropping a cannon ball into a pool of water with no air would look like. Would we see some splashing then?
It would look like a room full of vapour. You won't have liquid water in a vacuum for very long...
 

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