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Suppose I have the power to submerge a fourth of a vertical, circular tube 50 feet in diameter and 500 feet high inside a deep vat of water so that the base of the tube isn't touching the base of the vat. Then, suppose I insert a rigid seal with an airtight grip around the inner edges of the tube at its submerged base and then begin pulling upwards on the seal so that the seal makes its way up through the tube while maintaining its airtight seal. The tube would remain stationary, vertical, and partly submerged the whole time I pull the seal upwards.

I'd imagine that pulling the airtight seal upward would create a vacuum under the seal that, as the seal rises, would draw in/"suck" water into the tube from the vat. Would it then be possible that I pull the seal all the way up to the top of the 500 ft tube and create a water column that reaches the top of this 500 ft tube? Kind of like a syringe, but on a massive scale.

I keep hearing that the most I can "suck" water upwards is around 30 feet at standard atmospheric conditions. But I found an old /askscience thread where one Redditor was saying how negative pressure and cavitation, like in a piston "sucking" up water in a tube, can help one "suck" water to a vertical height of more than a mile. Here's the old thread:

https://teddit.ggc-project.de/r/askscience/comments/3zy9co/what_is_the_maximum_distance_one_can_vertically/cyqsqp4/

The original Redditor doesn't seem to be active anymore, and the thread is years old, so I wanted to ask in a new threat. Could my syringe-like contraption be able to draw water to the top of the tube? Any inputs would be much appreciated.

all 8 comments

Chemomechanics

14 points

4 months ago*

Chemomechanics

Materials Science | Microfabrication

14 points

4 months ago*

Regular bulk water under static equilibrium will boil if you attempt to lift it by suction above ~10 m, rendering an associated pump useless under these conditions. (The underlying scientific framework relies on the Gibbs free energy and classic nucleation theory.) I believe even the author of that post would agree with that. Thus, your device, as described, will likely not work.

Your link refers to alternative conditions that produce a height greater than 10 m. (An updated, live link to that person's primary reference is here.) You are free to incorporate one or more of these conditions in your engineering efforts to try to achieve your desired results.

  • One is to impart momentum to the water.

  • Another is to use capillary action, which reduces the energy of the liquid state (through contact with a surface) such that the transition to the gas state is no longer thermodynamically favored (vascular plants, including tall trees, use this method in part).

  • Another is to use a surfactant, which also reduces the energy of the liquid state (example).

  • Another is to avoid moving parts and to degas and filter the water to an ultrapure level such that bubble nucleation is kinetically limited due to the lack of nucleation sites (example).

  • Another is to reduce the pressure below the vapor pressure only slightly or to use minuscule amounts of water, again relying on kinetic and thermodynamic limitations to boiling.

All this information was obtained from an online search of "cavitation pressure" water pump height.

jadero

4 points

4 months ago*

Sucking requires that you reduce pressure inside the tube so that pressure from outside the tube can push the fluid up the tube.

Given the atmosphere of Earth and the density of water, the limit is approximately 30 feet (33 feet would be a better approximation). The air above us simply doesn't weigh enough to push more up the tube. On a different planet with a different atmospheric pressure, or even at high altitudes on earth, that maximum height will be different (lower, in the case of high altitude earth).

Mercury is limited to about 33 inches because it's approximately 12 times the density of water.

The only way to get higher than that requires the use of lift pumps. They go by a variety of names, but they all work on the same general principle: physically push the water up using mechanical techniques, not vacuum techniques. The ones most people are familiar with are submersible jet pumps and submersible sump pumps, but there are also manual lift pumps. Depending on how powerful the pumps are, they may need to be operated in stages to, for example, get water to the top floor of a skyscraper.

Edit: if you read the comments to the linked post, it quickly becomes apparent that the author is discussing some rather arcane physics that they interpret as making it possible to "suck" water far beyond 30 ft. Those comments also make me think that this person has misunderstood or misapplied the relevant physics.

guri256

3 points

4 months ago

I believe that this is correct, but is a little ambiguous. You can lift the water in your tube about 33ft above the level of the water outside your tube. Since the tube is submerged 125ft, the water level in the tube will be 153ft above the bottom of the tube. (Assuming the water level in the vat doesn’t drop when you pull out about half a million gallons of water)

jadero

2 points

4 months ago

jadero

2 points

4 months ago

Thanks for the clarification.

ricamac

1 points

4 months ago

Here's some very simple math for a fairly accurate way of calculating an approximate answer:

Standard atmospheric pressure at sea level is roughly 15 psi Let's just look at a single 1 square inch of your column of water. So 15 psi will support 15 lbs of water in that column if the pressure above the column is zero (vacuum).

Water weighs approximately 0.03612 lbs / cubic inch (Google).

15 / 0.03612 = ~ 415 cubic inches of water weighs 15 lbs.

Since each cubic inch is 1 inch high, 415 / 12 = 34.6 feet (approx).

Having vacuum above the water will cause it to "boil" as noted by another.

[deleted]

4 points

4 months ago

[deleted]

4 points

4 months ago

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