h a l f b a k e r yAssume a hemispherical cow.
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Current materials technology limits the pressures at
which gas can be stored. However, the absolute
pressure is not important, more the difference between
the pressure on the inside of the vessel and the outside.
So, if we take a very large vessel say at 100bar, inside
this
we can put a
smaller (1/2 volume) cylinder OF IDENTICAL
CONSTRUCTION at 200bar. So a 100m3 vessel that
would
normally be able to hold 100m3 at 100 bar could have a
50m3 vessel nested inside it. The original vessel loses
50m3 to the smaller vessel, however the smaller vessel
can
run at double pressure storing 100m3. The total would
be
150m3. A 50% increase. Inside the smaller vessel a still
smaller vessel could run at double the pressure again and
so on. Ideally this would all be controlled by pumps
situated on each nested cylinder, these would take gas
from the larger vessel and compress it into the smaller
ones. Valves would control release. This would simplify
the whole process having only one main fill/release port.
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Just how high a pressure are you trying to store gasses at? Standard scuba tanks, I believe, run upwards of 200 bar, and heavy industrial tanks can go significantly higher. |
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Your major limiting factor is not the tank design, but your pump/fitting strength. Your nested pumps would deal with this, but given the difficulty of servicing the nested pumps would offset the much of the advantage. |
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I was just thinking that the other day: if your next two posts concern hydraulic free piston engine efficiency I'm going to half-sue. |
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The app I had in mind was for a hydraulic system with the reservoir tank built around the accumulator tank. Upside of course is greater safety and smaller footprint. Downside is a greater surface area for the "sides" of the reservoir tank and hose, means pumping losses and, as MechE points out, more fiddlyness. |
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// difficulty of servicing the nested pumps// just turn the nested stopcock to the OFF position and proceed. |
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I'm pretty much in the dark when it comes to the
technicalities of pumping gas about to be fair. My
thinking was that you could peel away a layer so to
speak. So simply allow the gas in the outer most
chamber to fall to atmospheric (with the
corresponding percentage drop in all interior
nested tanks) then you can simply walk in and
service it while all of the inner layers are still in
service. Of course eventually you'll have to close
the whole thing down, or perhaps leave a robot in
there, or perhaps put more pumps in for redundancy. |
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What are you trying to save, though? I ask because you
could just make the outer tank of thicker, stronger
material. This of course would add cost and weight, but so
does having nested vessels. |
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One other thing: pressure vessels get stronger as they get
smaller: a small vessel can take more internal pressure
than a large vessel made of the same type and thickness of
material. So you need to compare the advantage of
nested vessels not just with a single vessel with thicker
walls, but also with a bundle of smaller vessels. |
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I was primarily thinking of space saving. Or possiby a
way of increasing the energy density of compressed
air for use in compressed air hybrid vehicles. Also if
you Google "gas storage" the overwhelming
impression is that of size. That, and I like the idea of
a large gas storage facility being painted like a Russian doll in honor of the technology inside. |
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// bundle of smaller vessels // |
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The MCP or "Multi Cylinder Pallet" uased for Hydrogen and Acetylene, amongst others. |
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This would probably work on the scale of a VLCC - sized gas transporter, but complexity/weight factors would tell against it on a smaller scale. And it's only useful for gas, not for liquid in equilibrium with its vapour. |
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Taking this to its logical conclusion, the innermost vessel should be as large as possible. So instead of being "nested" like Russian dolls, it's a multiwalled tank with each layer supporting the one inside. The amount of "dead" volume between each tank skin actually needs to be minimised for maximal efficiency; just enough room for the compressors and valve gear. |
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I'd thought of this, but thought the 50% thing would
come across better in the description. However I
kind of un-thought it, as with very small volume
layers, there's not a lot of buffering in the system on
fill up. But that's a minor criticism. |
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How much buffering does it need ? |
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You just need to control the pressure between the layers so they don't implode or explode. |
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In a reductio-ad-absurdum design, you could make the tank from layers of PVC membranes, each one capable of withstanding only fractions of a Bar, and yet the inner vessel would still be capable of crushing normal gas into degenerate matter ... |
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Is it relative pressure difference or absolute pressure difference which is important?
I'd have thought the latter : a vessel rated to 100 bar could stand 200 bar in a 100bar atmosphere, 300 bar in a 200 bar atmosphere and so on. |
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If that's the case, you can't double the pressure each time. |
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Otherwise you could presumably make even very high-rated vessels explode by tiny absolute pressure differences at near vaccuum. |
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So given that - is there any reason not to just make the external wall multiple times thicker? |
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//Taking this to its logical conclusion, the innermost
vessel should be as large as possible. So instead of being
"nested" like Russian dolls, it's a multiwalled tank with
each layer supporting the one inside. The amount of
"dead" volume between each tank skin actually needs to
be minimised // |
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And taking it to an even more logical conclusion, the
"dead" volume would be an interatomic gap, giving you a
single vessel with a thick wall. |
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Hahaha, beat you too it Maxey old boy. |
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hmm, but a vacuum is only around 1 bar below
atmospheric, so a 100bar vessel would be able to take
99bar in a vacuum surely? |
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That's quite amazingly profound, and yet somehow strangely not ... |
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I nearly put "vacuum atmosphere"... nearly. |
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This is essentially a bomb that goes off if the pressure of the outer vessel is somehow lost. |
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I'd thought of that, kind of a pressure domino effect,
but the same applies to normal pressure vessels, just
to a slightly lesser effect. |
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//hmm, but a vacuum is only around 1 bar below atmospheric, so a 100bar vessel would be able to take 99bar in a vacuum surely?// |
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Exactly.
In the idea you've assumed you can double the pressure in each vessel. That's fine for the first internal vessel, at 2x pressure in a 1x pressure environment. But for the next one, you propose 4x pressure, when it could only really take 3x pressure in the 2x -pressure environment. |
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Given that, you don't get any gain over just having a single container with a stronger wall. |
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And stop calling me surely. |
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[ldischler] -//essentially a bomb// - true, but the cool thing is that it goes off in steps as the shells blow. |
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Imagine how much Hollywood will love pyro FX of a bomb that just keeps going off! |
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That would be the perfect weapon for an assassin clown: nested helium balloons with a 1000 PSI core. |
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Horrible, terrifying, and yet strangely compelling ... |
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As the helium balloon can expand the pressure would
tend to equalize. |
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LORIS, you're right, dammit. The principle holds kind of true for the first one but none after that, bugger. |
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Really, stop voting this idea up, it's not so great, I'm
leaving it up as a thought experiment, one I went through
in reality and came out wiser... |
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//Really, stop voting this idea up//
Or what?! Hah |
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It's not a bad idea, just an irrelevant one. Making gas
bottles more compact is a lofty goal, but in the vast
majority of current applications for pressurized gas
(industrial and medical use), capacity vs. weight is more
important than capacity vs. volume. |
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You may be reasoning backwards. The current range
of applications for pressurized gas is probably
influenced by the current state of the art in
pressurized gas storage. Invent a system that
optimizes capacity per volume, and new applications
will* arise. |
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*So I assert. Seems to work that way, a lot, in
technology. |
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Possibly, but most situations that call for space-saving
measures also call for weight-saving as well. This idea
could feasibly pack 50-60 lbs of oxygen into something the
size of a 30 lb bottle, but would have a greater dry weight
than said, meaning my portable oxyfuel setup would be a
whole lot less portable, even when nearly empty. |
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+ has to be better than burning it off. Which they do. |
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The pump also works on pressure DIFFERENCE. So
pumping up from outer to inner should be possible
with the same equipment. |
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A better approach would be to mimic biology and
have a counter-current multiplier system. |
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You would constantly be pumping with minute low
energy pumps along pipes in pipes with the middle
section having extremely high pressure, actively
created from all directions. |
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Valves of these minute pumps should be remotely
controlled, for controlled hold of gas (closed valves)
and release (open). |
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//Valves of these minute pumps should be remotely controlled//
Perhaps offering gainful employment for some of Maxwell's demons. |
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I think this idea needs to be turned into its Bizarro twin. It is the perfect scheme for that philsopher's stone of LTA, the Vacuum Balloon. Each layer has less pressure until the center is 99.44% pure vacuum without the need for megastruts or the like. |
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// It is the perfect scheme for that philsopher's stone// |
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No. The perfect scheme for that philosopher's stone is gallbladder surgery. |
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Perhaps, but "Harry Potter and the impromptu gall-bladder operation to remove calculi" probably wouldn't have made Ms. Rowling the millionairess she is today... |
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