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RASCaL
Water + electricity = fast! | |
(Another one that's been evolving in my head...)
Ever since seeing the Mythbusters explode a domestic water
heater, I've wanted to use that "steam explosion" in a useful
way.
There have been steam cannon concepts in the past (way back
to Archimedes), but they are all quite pitiful (IMHO...).
They all
simply heat up an empty vessel behind the breech (with the
projectile in place), then spray in a little water, which flashes
to a little steam & bang! Projectile goes pfft.
Rather, have the projectile held in place in the breech. Behind
it, the heated vessel is completely full of water, which gets
heated (electrically) to 400°C or so. Because it is contained, the
water can't turn into steam & goes super-critical, raising the
pressure. A lot.
Once everything ready, the clamps holding the projectile let go.
Suddenly the supercritical water finds that it is no longer under
pressure, & it flashes to steam, increasing it's volume by ~800x.
This makes the projectile leave in a hurry. If my calculations are
correct (questionable...) 2 litres of water heated 400°C & a 1kg
projectile gives (theoretically) 2,592m/s, about Mach 7.6; there
will obviously be losses.
Then I discovered ram accelerated projectiles.
Like a ramjet, RAP cannons require the projectile to already be
going fast; then it goes faster. So it becomes "Stage 2" to the
steam cannon.
In keeping with the "electricity + water" theme, I figured
hydrogen & oxygen (split water) would be a convenient fuel for
the RAP stage (whether it's the BEST option, TBC). A
modification I haven't seen in digging around RAP research is to
have a non-constant radius to the barrel; as the projectile
accelerates, the barrel (radial gap) decreases to provide more
compression. Multiple stages allow changing initial pressure of
the H/O2 mix; a simple stretched plastic film between will
probably be enough, except right at the muzzle, where a fast-
acting mechanical door will have to be used.
Since it will be big & very slow, the primary use I see would be
micro-satellite launching. Maybe hang it from a balloon, or
mount it along the whole length of an aircraft.
So, a Ram Accelerated Steam Cannon Launcher. RASCaL.
(I'll link models & drawings when I sort out my Photobucket.)
[link]
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I think the principle is fine, its the niggling details of making the breech walls and the containment clamps and the seal between breech and projectile strong enough that might cause some* issues. |
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*i.e. complete failure to do anything |
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That's not fair, [poc]. If the water is heated to supercritical you're GUARANTEED to have a boom. It may or may not be a disassemblish boom, but boom it shall. |
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//If//. A leaky seal will stop it going supercritical. |
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At what pressure does Hydrogen and oxygen ignite on it's own? I imagine the springy heat energy of all the supercritical water molecules will be more than the energy released of a lesser amount of hydrogens and oxygens moleculing up. |
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How many goes you would get from the precision sealing would be an cost issue. |
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[wjt]; good point. A (very) quick search said nothing about
pressure, but auto-ignition occurs at 570°C at 1 Bar (which
would actually help; it wouldn't need an independent ignition
source). I would assume higher pressure = lower temperature. |
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