h a l f b a k e r yBirth of a Notion.
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So, LOX is a very nice oxidiser for rockets, but it is a
nuisance because of its very low temperatures. It's also a
nuisance to have to pump the LOX and the fuel (kerosene,
liquid hydrogen etc) seperately.
It is possible to make monopropellants by mixing LOX with
various hydrocarbons. However,
such mixtures are
fantastically sensitive and are, basically, explosives
waiting to happen.
Now, two things.
First, it is possible to produce fantastically uniform
droplets, and droplets-within-droplets, using microfluidics.
Second, a very tiny (say, 100um or less) spherical container
can support a fantastically high pressure, compared to a
larger container made of the same material. (It's all to do
with cube-square laws).
So, I contend that it should be possible to make small
(100um, maybe much smaller) capsules consisting of a thin
polymer shell filled with LOX. These would be made at
atmospheric pressure and low temperature, but would then
remain intact as their LOX contents reached room
temperature. (Strictly speaking, at room temperature the
oxygen would become a dense gas at very high pressure,
since we're above the triple point of oxygen. But the point
is that the amount of oxygen in the capsule remains the
same).
The capsule material needs to be non-reactive with high-
pressure oxygen at ambient temperatures, but should
break down (and, ideally, combust) above some high
temperature (say, a few thousand degrees).
You can now use these little capsules in various ways. One
way would be to mix them with a fuel such as kerosene,
and pump this fine slurry into the combustion chamber,
where the heat of combustion is sufficient to rupture the
capsules. Pumping the slurry without rupturing the
capsules (which would cause combustion within the pump)
might be difficult, though.
An alternative would be to set these capsules in wax (or
any other suitable fuel), to produce a very high-impulse
solid rocket fuel.
Sprengel explosive
http://en.wikipedia.../Sprengel_explosive
Prior Art [8th of 7, Sep 03 2012]
[link]
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Ha - thought this was going to a spray on flavour for toasted bagels. |
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// mix them with a fuel such as kerosene // |
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One capsule fails ... releasing pure oxygen under very high pressure into a flammable liquid hydrocarbon. Oxidation immediately starts, analogous to the Diesel cycle, and a shock wave propagates out, causing another nearby capsule to fail, boosting the wavefront ... the temperature rises rapidly, a third capsule fails due to a combination of heat and shock, the reaction is boosted, a couple more capsules break ... |
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Ummm, this looks strangely familiar ... |
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// Pumping the slurry without rupturing the capsules (which would cause combustion within the pump) might be difficult, though. // |
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// An alternative would be to set these capsules in wax (or any other suitable fuel), to produce a very high-impulse solid rocket fuel. // |
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... previously known as a "Sprengel" explosive <link> |
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//One capsule fails ... // Yes, it would be quite
preferable if none of the capsules failed. But
that's not an impossible request. For one thing,
the capsules can be shaken, beaten, and generally
abused before they are mixed with the fuel, to
weed out any dud ones. |
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Also, it's not clear that the rupture of a single
capsule (releasing a few picolitres of highly
compressed oxygen, equivalent to a few picolitres
of LOX) would initiate a catastrophic chain
reaction. |
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And yes, Sprengel explosives, but they are
different and entirely too exciting. |
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// entirely too exciting // |
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You're no fun anymore ... |
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That's what my assistant pyrotechnician says. |
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Oh, you've managed to hire another ? Despite what the Coroner said at the previous inquest but one ? |
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The coroner and I have an understanding. I put a lot
of business his way. |
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Two types of capsules...one with oxygen, and the other with
hydrogen. Fire them at each other, and the heat of collision is
used to ignite the contents. They could be fired at reach other
using maybe an electrostatic charge, or magnetic field. |
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I do like the way one uses one's lab assistants to shake cocktails. |
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//a very tiny (say, 100um or less) spherical container can support a fantastically high pressure, compared to a larger container made of the same material. (It's all to do with cube-square laws).// |
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I think the neurons took a left turn at Albequerque. How does size have anything to do with it except, at the microscopic level, if you were bending the bonds between atoms (buckminsterfullerenes etc) and molecules. |
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Make them small enough and you will have a noticeable amount of O2 sneaking out through all the cumulative square footage of container material. |
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<grabs bowl of popcorn...> |
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You might want to think a moment before biting down on that stuff [2fries] ... do you know where it came from ? There's a lot of starch and cellulose in there, right ? |
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Just go check the trash for any "MaxCo Super Popping Popcorn (1.1D)" cartons ... look for the orange-and-black HazChem diamonds, they're quite distinctive ... |
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Will do. Now as to [FlyingToaster]'s question... |
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<heads back to kitchen for a dash of salt> |
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Red oxygen, O8, is quite interesting, and seems to be formed at
pressures over 1.4 million psi. Spherical hoop stress is internal
pressure x radius / 2 x thickness. |
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If we choose a good steel of 100,000 psi yield then thickness of
the sphere's wall is 7x the radius, for any radius. |
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Could this be added to wallpaper paste? |
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//How does size have anything to do with it // |
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It's to do with physics. Basically, if you make a big
spherical shell and a small spherical shell with the
same wall thickness, the smaller one will take a
higher pressure before rupturing. |
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If you want experimental evidence, search
youtube for the experiment where two soap
bubbles are connected by a tube. The smaller
one shrinks and the larger one grows, because the
smaller bubble has a higher internal pressure even
though the stress in the walls (which, in this case,
is just the surface tension of the soap film) is the
same in both. |
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If you want the maths, think of the internal
pressure as trying to split the shell in two across
its diameter. The force trying to do this is
proportional to the cross sectional area of the
sphere (ie, proportional to the square of the
radius), whereas the amount of material that has
to be split is proportional to the circumference of
the sphere (hence proportional to radius).
Therefore, the pressure that can be contained is
inversely proportional to the radius of the bubble. |
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([Ling] alluded to this in pointing out that the
spherical hoop stress is proportional to the
radius.) |
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At STP, a closed vessel initially full of LOX will
attain a pressure of about 1300 bar. |
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Now, a regular oxygen cylinder has a diameter of
maybe 25cm and a wall thickness of 6mm, and can
sustain a pressure of at least 200bar (with a
margin). So, we can assume that a sphere of 25cm
diameter and 6mm wall thickness is easily capable
of taking 200bar. |
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We want to take 1300bar which, if the sphere were
25cm across, would need a wall thickness of about
40mm. |
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However, as noted in the last annotation, wall
stress is proportional to the diameter of the
sphere. Hence, wall thickness can change in
proportion to the sphere's diameter. |
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Thus, for a 100um sphere, the wall thickness to
contain 1300bar need be only 16 microns. |
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If we make the LOX spheres only 10µm in
diameter, we can use a 1.6µm shell. These
dimensions are easily attainable by microfluidics
(although I have not seen µflu devices designed to
operate at cryogenic temperatures, which would
be needed to create and fill these things). |
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Of course, we would not want to use steel, but
instead a polymer which would decompose at high
temperatures. Some of the good engineering
plastics might work nicely, as long as they do not
react with oxygen at high pressure and standard
temperature. |
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Ah, hang on, I just realized that this is exactly what
[Ling] pointed out. |
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