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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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//a hot-water- vapour balloon will lose heat at a ferocious rate// |
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Link 2 mentions a double walled ballon. |
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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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This is entirely too similar to [Steam Balloon] to stand as it's own post. I could understand not knowing about Steam Balloon if it was in a different category, but it's in the same category! HUGE FISHBONE for obvious prior art. [-] |
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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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