h a l f b a k e r yA few slices short of a loaf.
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A dimer, or a thermoset would be best. |
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But you've set a tough target, creating "vacuum foam". The overall mass of the sphere needs to be lower than the density of air, and still be able to resist 1Bar without collapsing. It needs to be non-porous, rigid, but not brittle. |
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Wall thickness will be critical; too thin, and the sphere will collapse - too thick, and it will be too heavy. |
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Rather than a polymer, Titanium might be closer to the mechanical properties you want. |
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Hey, titanium melts. If you can melt it, you can blow a
bubble with it. |
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But yea, you've got that catch 22 of needing enough wall
to hold up to that vacuum without being lighter than the
air it's displacing. |
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Sounds like a job for somebody who knows science 'n stuff
with like, math 'n whatever. |
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It should not be possible to blow bubbles in a vacuum. |
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According to an answer given at the physics stack exchange bubbles could be formed in a vacuum. [link] |
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I'm struggling to see the advantage here over making a
sphere and sucking the air out. |
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I vaguely remember a lecturer in 1st year proving that the
weight of a sphere made out of any currently known
material would be too great to allow a vacuum balloon to
work, given the material strength. I can't remember exactly
as it was a while ago - it should be a fairly simple proof I
think. |
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With this you could make several hundred a minute. |
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If there is a material that would work. |
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How about making an oblate spheroid with progressively
thicker, stronger material at the poles then rotating it at high
speed? The centrifugal forces would partially counter-
balance atmospheric pressure on the thinner material at the
equator. |
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Someone else can come up with an solution for the
atmospheric drag issue. |
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The difference of being able to blow a bubble and pull a bubble with suction from all sides, is probably a universal asymmetry. |
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I was also thinking that the advantage of this over just
blowing a balloon, hardening it and sucking the air out is
you've got minimum stress on the sphere during the
process. You've got no turbulence when sucking the air out
therefore no vibration and less stress on the structure of
the envelope. |
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Yes, there is air coming out of the balloon when you open
one end to the vacuum to let it out, but since it was blown
in a vacuum very little air was needed and the only time
you put pressure on the thing is when you let it out of the
chamber into the atmosphere. But then any stress on the
structure is very even without currents and eddies of
airflow buffeting the hole where you're sucking the air
out. |
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Creating a vacuum balloon that is strong enough to hold up
to the vacuum yet lighter than the air it's displacing would
require some pretty precise manufacturing. This would be
one way. |
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That being said not sure if any material short of
diamondium would be able to handle the job so this is
more of a look at a different way of manufacturing
something than an actual practical idea, despite the word
"practical" being in the title. |
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If you could create some kind of lattice inside the ballon
during the process, it might better resist the buckling that
tends to be the downfall of vacuum balloons. |
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Filled with plastic foam where you evacuate the gas after
it
hardens? |
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Or blow multiple bubbles of some sort or another? See
link. |
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I think there's a number that some material would need to
achieve, titanium being X meaning strength per pound and
to have a bubble that could sustain a vacuum you'd
probably need something like 1/10th X. |
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//The difference of being able to blow a bubble and pull a bubble with suction from all sides, is probably a universal asymmetry.// |
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No - they're exactly the same thing. To blow a bubble, or to inflate a balloon, the pressure inside must exceed the pressure outside by a certain amount, X. X is the surface tension (of a bubble) or the resilience (of a rubber balloon). |
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So, you can blow a bubble in a vacuum by supplying just enough internal pressure to overcome surface tension. (It's no different to blowing a bubble in air, except that both the internal and external pressures are reduced by about 15psi in a vacuum.) |
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There is one difficulty with blowing bubbles: the pressure needed to overcome surface tension decreases as the bubble gets bigger. So, if you provide enough pressure to get the bubble started, and then maintain that same pressure, the bubble will inflate faster and faster and then burst. (Much the same is true of balloons, though the physics is a bit different.) So, you need to inflate a bubble by volume, not by pressure. |
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Seems to me that to make a vacuum balloon you need to
make it out of a material that is resistant to buckling.
The skin of a bubble isn't it. I imagine a material like
foam board with two high tensile strength skins
separated by a low density core that resists compression
would be one direction to look. ON second thought, I
doubt any type of foam would work because a randomly
created foam tends to be compressible to some extent. |
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I think what would be needed is a truss. To save weight,
the members of the truss are probably also small trusses:
so a fractal-like truss. A lattice in the balloon sounds
good, but needs to be very sparse. I'd say a fractal truss
around the surface with a relatively small number of high
tensile strength fibers through the center of the sphere
to hold the overall shape. |
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It seems like someone might be able (or has tried and
failed) to design such a structure using simulations tools.
Once designed, it seems like it would be incredibly
difficult to build, but the design itself would be
interesting and might inspire someone to figure out how
to physically create such a thing. |
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What you want is an incredibly stiff material - specifically, a high specific (ie per-weight) Young's modulus. Pure compressive strength isn't an issue - thin shells fail in buckling, as noted. |
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