h a l f b a k e r yMay contain nuts.
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Picture if you will, a standard issue rockoon, climbing its way into the sky. Expanding as the atmosphere thins around it. Eventually expanding to the limits of your (initially crumpled and raisinlike) balloon. But yet there is more atmosphere to be traversed. What to do?
One could shrug, ignite
the rockets, fire the cannons and hope for the best. One could burn off hydrogen released from the expanding balloon to generate a puny rocket of sorts - probably not much compared to the bloated balloon it is trying to lift. Plus, all of that heat is wasted as the hot gas shoots from the rocket.
I propose that excess hydrogen be burned inside the balloon. In a controlled fashion, of course. This would be analogous to a low altitude hot air baloon where a jet of hot gas is shot up into a shell to provide lift.
Here, excess hydrogen (excess because of expansion at altitude) would be burned to heat the remainer of the hydrogen within the balloon, making it more buoyant. Burn control would be achieved by limiting the oxygen available. Oxygen could be carried with and released as a function of internal balloon pressure. Or, to save weight, ambient air could be used - producing a less vigorous combustion at high altitude but contaminating the baloon interior with worthless nitrogen.
The hot balloon would be even liftier and could gain more altitude than a cold balloon. Energy from burning lift hydrogen would be put to good use as captured heat. Water produced from the burn would condense on the balloon interior and run the the bottom of the balloon and out a special valve, from which it would trickle gently from the skies onto the gathered families of less talented N-prize competitors.
Big band to outer space
Big_20Bang_20to_20Outer_20Space
My inspiration. This one blows up real good. Real good! [bungston, Jan 23 2009]
[link]
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I think the advantages are small, but I'm bunning for "liftier". You'd have to carry a good bit of O2 to burn the H2 and that's going to eat up the small gains. I was wondering if there was a light smoke that you could blow into the hydrogen to allow solar heating of the gas. |
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AC Clarke's "A meeting wih Medusa" describes a hot hydrogen balloon, albeit in the atmosphere of Jupiter. |
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//was wondering if there was a light smoke// I don't think there'd be any advantage over a simple black envelope. |
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It would be tricky to balance everything. Heating
hydrogen would expand it and increase the
pressure, which would cause more hydrogen to be
burned, which would heat the hydrogen, etc.
After all of that burning you'd still have a lot of
water vapor mixed in that hasn't condensed yet -
once it condenses the balloon will shrink. |
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I say keep the hydrogen pure. Have a tube run
through the center of the balloon, acting as a
propulsion jet, a burning chamber, and a heat
exchanger. Air enters from the top, hydrogen is
introduced and both are ignited firing downward.
The products of combustion transfer their heat to
the balloon as the travel downward, and are
jetted out the bottom for upward lift. No useless
nitrogen, no heavy water vapor, and less balloon
collapsing once you reach your peak. |
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//Big band to outer space //
Tommy Dorsey? |
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Good thoughts World. I am wondering about the water vapor
as a physics problem. What has more lift, a balloon of gas and
water vapor a temperature x or the same balloon now with
only the hydrogen at temperature x - y? |
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Of course, reacting away your lift gas is not a good way to
maintain lift in the long term, which was your point. |
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Instead of creating a fire by sending air/oxygen into the envelope, with combustion happening as the air diffuses into the hydrogen, take the hydrogen out of the envelope, mix it with ambient air, burn it, send it through a heat exchanger, which heats hydrogen being circulated from the envelope, then expell the air/water vapor exhaust out to the atmosphere. |
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I'm considering entering the N-Prize with a team of mentally acute people who will hold hands around the satellite and will it into space. |
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I have been pondering the change suggested by World and
goldbb. Of course, they dispense with the beauty of an open
flame surrounded by hydrogen. They would however be much
more practical. |
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As World suggests, a chamber inside the balloon connects
with the outside via a coiled tube within the balloon. A
rubber valve on the chamber allows H2 to fart in as the
balloon rises and with it its internal pressure. A 9V battery is
rigged so that it sparks every few seconds. When there is
combustion, atmospheric gas that has come up the tube (and
supported combustion in the chamber) is propelled back out.
Water vapor within the tube then condenses on the walls,
delivering its heat, and drips out. |
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//Hydrogen is light. Hot hydrogen is lighter// |
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Yeah, but not much. Hydrogen already has 93% the lifting power of a vacuum. If you heat it 100K from a stratospheric temp of 270K, then that takes you to 95%, a 2% increase. The effect is much less than you'd get with a hot air balloon because hydrogen weighs so little to begin with. And when you add in the weight of your burner and condenser, and you'll probably have a net loss in lift. |
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<to music>
Captain: See Marlene, sun shines through the rain
Marlene: No, that's an airship, why don't you come around again?
Captain: It must be at its ceiling...
Marlene: Is it burning, an internal flame? |
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//Also, to get enough hydrogen to reach the moon you need about 200l of H2 per kg and 100l of oxygen which gives more than enough lift.// |
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Ah! Miasere is really Dr Andrew Grant, travelling companion of Sir John Herschel. |
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