Live data from Hacker News

Water compresses under a high gradient electric field

phys.org

41–49 of 49 posts

Re: Water compresses under a high gradient electric field

#41
post #38

What would happen if you compress water using this method and then seal the container it's in and turn off the electricity? Anything interesting? Does the water stay compressed? Does the container explode? Does it depend on the strength of the container?

Intuition says that the water would then exert more pressure on the container. Like if you emptied and sealed a plastic bottle while at sea level, and then ascended to a high altitude in an airplane (or climb a mountain). The bottle would be bloated. Whether or not it would explode depends entirely on the properties of the container..

Would not the bottle be squished now that it is under more pressure?

Re: Water compresses under a high gradient electric field

#43

Earlier quoted context omitted.

Intuition says that the water would then exert more pressure on the container. Like if you emptied and sealed a plastic bottle while at sea level, and then ascended to a high altitude in an airplane (or climb a mountain). The bottle would be bloated. Whether or not it would explode depends entirely on the properties of the container..

Would not the bottle be squished now that it is under more pressure?

Yea, you're absolutely right, I swizzled the analogy. I fixed my previous comment. Thanks :)

Re: Water compresses under a high gradient electric field

#44

It's always surprised me how many people do not know that water is incompressible! For example, when someone is filling a scuba tank, it's common to put the tank in a large, often metal-sided container of water. When asked why, the shop staff member will typically say: "In the unlikely event of the tank blowing up, the water will absorb the force of the explosion." But in fact, water being incompressible, it will abs…

> It's always surprised me how many people do not know that water is incompressible! Interestingly enough, they're right (though they may not know it) since the article is about its ability to compress under the right circumstances!

But only by 3% - so I still won't set up my chillout lounge right next to the tank fill station! :-)

Re: Water compresses under a high gradient electric field

#45

It's always surprised me how many people do not know that water is incompressible! For example, when someone is filling a scuba tank, it's common to put the tank in a large, often metal-sided container of water. When asked why, the shop staff member will typically say: "In the unlikely event of the tank blowing up, the water will absorb the force of the explosion." But in fact, water being incompressible, it will abs…

It's definitely both the cooling (otherwise the cylinder would get hot, just like a can of duster gets cold), and the safety thing. The walls of the container would generally be more than enough to withstand the acoustic shock and send that energy upward as a burst of water, but your real enemy is shrapnel from the cylinder, which the water will promptly slow to non-lethal speeds. I'll agree that a guy doing it in a plastic tank or a smallish metal one would be asking for trouble.

Re: Water compresses under a high gradient electric field

#46

It's always surprised me how many people do not know that water is incompressible! For example, when someone is filling a scuba tank, it's common to put the tank in a large, often metal-sided container of water. When asked why, the shop staff member will typically say: "In the unlikely event of the tank blowing up, the water will absorb the force of the explosion." But in fact, water being incompressible, it will abs…

On the flipside, water is used for the periodic pressure testing of scuba tanks, precisely because it is essentially incompressible. So if a tank does blow up during testing, you have a very small expansion and thus very small energy release.

If you draw a curve of gauge pressure as a function of volume, the energy release is the area under the curve, and as the curve steepness goes to infinity (i.e. compressibility goes to zero) the energy released starting at a given pressure goes to zero.

Re: Water compresses under a high gradient electric field

#47

It's always surprised me how many people do not know that water is incompressible! For example, when someone is filling a scuba tank, it's common to put the tank in a large, often metal-sided container of water. When asked why, the shop staff member will typically say: "In the unlikely event of the tank blowing up, the water will absorb the force of the explosion." But in fact, water being incompressible, it will abs…

On the flipside, water is used for the periodic pressure testing of scuba tanks, precisely because it is essentially incompressible. So if a tank does blow up during testing, you have a very small expansion and thus very small energy release. If you draw a curve of gauge pressure as a function of volume, the energy release is the area under the curve, and as the curve steepness goes to infinity (i.e. compressibility…

I did know that, but I'm not sure how that applies. In your scenario, the tank ruptures, there's virtually no water expansion, so nothing happens. In my scenario, the tank ruptures, the internal gas content instantly expands by (say) 250 times, creating a massive force which I assume is transmitted virtually undiminished, through the water, to the sides of the container, which promptly explode outwards. I do accept that some of the force will go upwards, but I believe the container will still explode. Not really trying to disagree, just trying to get my head around it :-)

Re: Water compresses under a high gradient electric field

#49

Earlier quoted context omitted.

On the flipside, water is used for the periodic pressure testing of scuba tanks, precisely because it is essentially incompressible. So if a tank does blow up during testing, you have a very small expansion and thus very small energy release. If you draw a curve of gauge pressure as a function of volume, the energy release is the area under the curve, and as the curve steepness goes to infinity (i.e. compressibility…

I did know that, but I'm not sure how that applies. In your scenario, the tank ruptures, there's virtually no water expansion, so nothing happens. In my scenario, the tank ruptures, the internal gas content instantly expands by (say) 250 times, creating a massive force which I assume is transmitted virtually undiminished, through the water, to the sides of the container, which promptly explode outwards. I do accept t…

I'd have to do the math (and know the material properties and thickness of the tank walls) before saying one way or the other, whether that scheme is effective.

What it could also be doing, is keep the tank from going off like a missile through the building (added inertia of the water plus it takes much longer for the tank to tip sideways).

Post reply on HN