h a l f b a k e r yIt's as much a hovercraft as a pancake is a waffle.
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[Edited: See link to identical Steam Balloon, to actual
balloons of this sort since the mid 1850's and to a patent
about the shape of the balloon]
H2O is lighter than O2 and N2 - reason even clouds
(liquid water particles!) float.
So all we need to do is fill a balloon with water vapor
(not steam) and keep it hot. any water condensing on
the inside shell should drip (by tiny points meant for
this) back down to the heater. Perhaps the heating
should be all along the balloon shell and not only at one
point on the bottom. Also reconsider the shape because
of this requirement, so that water is quickly dropped
from the walls back to the heater(s).
Steam flight in history
http://www.flyingkettle.com/priorart.htm
[xaviergisz, May 14 2009]
More prior art (2006)
Balloon_20Notions
A hot-steam balloon is proposed, including some calculations, among other things. I didn't know about [supercat]'s 2002 posting of this Idea, at that time. [Vernon, Jun 24 2011]
The other Jean Paul
Aerofeather
[pashute, Aug 14 2011]
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//water vapor (not steam)// - in what way is it not? |
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Can't see why this wouldn't work... In fact it seems like a pretty good idea. You'd need insulation on the baloon skin, as the temperature inside would need to stay above 100 degrees at sea level. Obviously the higher up you are, the lower the temp needs to be, in terms of keeping the water gaseous. |
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lurch, pashute was probably trying to distinguish between water vapor and the fine mist condensation that often accompanies water vapor. From the wikipedia article on steam: |
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In common speech, steam most often refers to the white mist that condenses above boiling water as the hot vapor ("steam" in the first sense) mixes with the cooler air. This mist is made of tiny droplets of liquid water, not gaseous water, so it is no longer technically steam. Pure steam is present at the base of the spout of a steaming kettle where there is no visible vapor. |
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I like it. Water is cheap and safe. This would be contained
like a helium balloon but full of water. You could model it
with a big mylar balloon and an heating element (auto
cigarette lighter?) powered by a 9v battery. |
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I like it.
density of hot air (99°C): 0.95 g/l
density of water vapor: 0.8 g/l |
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What is the efficiency of heating a litre of air compared to heating a litre of water vapor? |
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This is an interesting idea, I think. But first, the opening
statement about clouds is a red goose chase. Clouds are
only visible because they are a group of liquid water
droplets hanging around together. The droplets
themselves are as dense as any other water (ie, about a
thousand times denser than air); the only reason they stay
up is that they are tiny, and hence have a huge relative
surface area and enormous drag. Therefore, in still air
they will fall very slowly (just as iron filings would sink very
slowly in honey), and any small updraft is enough to keep
them aloft. |
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But that's not the point. Water vapour (ie a gas) is, as you
point out, less dense than air, so this should work. I think
your main problem will be keeping the air hot. |
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If you have a balloon full of air at 100°C, the air near the
walls will be at about 20°C (or whatever the outside air is),
but this is fine: that first layer of air insulates the rest of
the air in the balloon (apart from convection, which
disturbs it a little). The skin of the balloon stays quite
cool because of the boundary layer of cool air. |
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However, suppose you had a balloon full of water vapour at
100°C. The vapour near the walls will quickly cool to
ambient temperature but, as it does so, it will condense
onto the walls, heating them up to almost 100°C. As it
condenses, of course, more hot vapour must move in to
take its place, and so on. For that reason, a hot-water-
vapour balloon will lose heat at a ferocious rate: there will
be no insulating boundary layer, and the walls will always
be at 100°C. |
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How much energy would it take? A lot. Your household
radiators have a surface area of maybe one or two square
metres, and are kept at (say) 70°C (50°C above ambient);
each one uses maybe a kilowatt of power. Now imagine a
balloon with a surface area of several hundred square
metres at 100°C (80°C above ambient)- it's going to need
something on the order of a megawatt to keep it hot. |
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Most materials used in balloon making - selected for strength/weight ratio, imperviousness (or coatability to obtain such), and resistance to elevated temperature - won't tolerate the higher temperature you'd need for water vapor. |
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Plus, heated water vapor is extremely active chemically - in ways that cloth generally doesn't like. |
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I think you'd have to use a material - say, aluminized mylar, for example - that would not typically be employed for a man-rated balloon for safety reasons. If you get a good material that'll handle it, you'll probably negate a good amount of the lift advantage with the added weight. |
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If you have to do a dual-layer envelope, then there goes even more of the advantage. |
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This idea has been halfbaked, baked, patented, but never really seen actual service. The impression that I get is that it's not impossible, but sufficiently difficult that it loses its appeal. |
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I was tempted to [m-f-d] this because of the prior art "Steam Balloon" (I'll get around to linking it later, if someone doesn't beat me to it), but decided against it because I think that there's points here not covered before. |
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I was thinking about a conventional hot air ballon. Suppose it were full of hot water vapor. A collection cuff on the interior could route condensed vapor into a pipe that took it back to th heat element. |
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For the heat element you would use the standard gas jet, which I think burns propane. Adding the water would cause this jet to emit a hot CO2 / H20 mix: greater lifting power, and so more economical with the propane. |
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But probably not practical. Max, that was a trenchant and excellent analysis of the problems of water as a lift gas. I likes. |
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I kind of like it for a couple of reasons.
I think that it should be possible for at least a large portion of the lifting gas to be water vapor using nothing more than solar energy and black plastic, and it would be an efficient meathod for transporting water this way in arid climates even if the balloons had to be tethered to another means of transport. |
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Sorry, I somehow missed the "steam-balloon" I REALLY DON"T KNOW HOW!. I'm always excited when I find that (the 4 or 5) ideas (a day) I have, have already been written in the Halfbakery, discussed, patented and actually created. Anyway, because its such an interesting discussion, lets leave it please and not delete it. |
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And yes, I meant "not steam" - not mist, in other words gaseous water which is not seen. |
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I edited the entry to point to the Steam Balloon. |
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Or you could paste the entire discussion of this idea as an anno in steam balloon. It is not so long. |
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er. jutta, what do you say? |
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[jutta] answered in email that its better to leave the discussion because people can then delete or change their annos. I'm linking from there to here. |
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the math supports steam ballons, since the specific heat capacity of water is several times that of air, while it would take a long time to generate enough steam to lift off, once inbound it would take a much longer time for the envelope to cool. It would basically be a "heat battery" the boiler on board would just be enough to replace the reboil the condensation faster than it's formed |
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secondly due to the higher lift capacity of steam, the envelope would be smaller thus having a lower surface area exposed to ambient temperature further increasing efficiency. You could also paint the balloon black to increase the envelope temperature and get some free solar heating. The difference in lift capacity would more than allow you to attach lightweight insulation such as aerogel. |
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my favourite part is that you could attach a small steam engine to the balloon to power a propeller. The envelope would then act as a condenser and economizer, essentially you would have a 99% efficient system, the only waste energy would be heat that didn't make it into the envelope. Also any condensed water could be stored to act as ballast for when you want to come down or converted back into steam if you want to go up essentially letting you lift off with 0 ballast but gain some if needed. |
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In the modern globalized economy in order to capitalize on this invention, you could install a steam cleaning nozzle and operate the worlds first mobile steam cleaning business to impoverished villages around the world, becuase everyone wants crisp steam cleaned clothes. |
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A few people here think that water vapour in the air as to condense out as soon as the temperature drops below the boiling point of water. In fact air can be kept supper saturated with water vapour, down to minus 15 C.
the challenge is the elimination of condensation nuclei. |
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— pashute, Have you considered a thermal fogger as your boiler? |
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j paul, are you j.p.david from the Aerofeather
personal blimp? |
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No I’m J P Fellows from Middlesbrough! |
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If the balloon were surfaced with one way reflective foil as is done on limosine windows, sunlight could get in but not out. This might not be enough to boil it but would help. The balloon could be used in daylight in sunny areas. |
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Sounds better than my hot hydrogen balloon. (May the pilot and crew R.I.P.) |
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Dont remember in which idea, but I was almost eaten
to the bone about "one way mirrors". There's no such
thing. But thanks bungs. |
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