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Granular LOX

Tiny bubbles of oxygeny goodness
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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.

MaxwellBuchanan, Sep 03 2012

Sprengel explosive http://en.wikipedia.../Sprengel_explosive
Prior Art [8th of 7, Sep 03 2012]

[link]






       Ha - thought this was going to a spray on flavour for toasted bagels.
xenzag, Sep 03 2012
  

       Who says it can't be?
MaxwellBuchanan, Sep 03 2012
  

       // mix them with a fuel such as kerosene //   

       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 ...   

       Ummm, this looks strangely familiar ...   

       // Pumping the slurry without rupturing the capsules (which would cause combustion within the pump) might be difficult, though. //   

       Really ?   

       // An alternative would be to set these capsules in wax (or any other suitable fuel), to produce a very high-impulse solid rocket fuel. //   

       ... previously known as a "Sprengel" explosive <link>   

       Intriguing idea, though.   

       [+]
8th of 7, Sep 03 2012
  

       //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.   

       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.   

       And yes, Sprengel explosives, but they are different and entirely too exciting.
MaxwellBuchanan, Sep 03 2012
  

       // entirely too exciting //   

       You're no fun anymore ...
8th of 7, Sep 03 2012
  

       That's what my assistant pyrotechnician says.
MaxwellBuchanan, Sep 03 2012
  

       Oh, you've managed to hire another ? Despite what the Coroner said at the previous inquest but one ?
8th of 7, Sep 03 2012
  

       The coroner and I have an understanding. I put a lot of business his way.
MaxwellBuchanan, Sep 03 2012
  

       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.   

       I do like the way one uses one's lab assistants to shake cocktails.
Ling, Sep 03 2012
  

       //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).//   

       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.   

       Make them small enough and you will have a noticeable amount of O2 sneaking out through all the cumulative square footage of container material.
FlyingToaster, Sep 03 2012
  

       <grabs bowl of popcorn...>   

       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 ?   

       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 ...
8th of 7, Sep 03 2012
  

       Will do. Now as to [FlyingToaster]'s question...   

       <heads back to kitchen for a dash of salt>   

       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.   

       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.
Ling, Sep 04 2012
  

       Could this be added to wallpaper paste?
xenzag, Sep 04 2012
  

       or wasabi paste?
not_morrison_rm, Sep 04 2012
  

       //How does size have anything to do with it //   

       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.   

       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.   

       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.   

       ([Ling] alluded to this in pointing out that the spherical hoop stress is proportional to the radius.)
MaxwellBuchanan, Sep 04 2012
  

       OK, some calculations.   

       At STP, a closed vessel initially full of LOX will attain a pressure of about 1300 bar.   

       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.   

       We want to take 1300bar which, if the sphere were 25cm across, would need a wall thickness of about 40mm.   

       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.   

       Thus, for a 100um sphere, the wall thickness to contain 1300bar need be only 16 microns.   

       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).   

       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.
MaxwellBuchanan, Sep 04 2012
  

       Ah, hang on, I just realized that this is exactly what [Ling] pointed out.
MaxwellBuchanan, Sep 04 2012
  
      
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