Water Vampires in the Sky

I am in the midst of a 12,000 mile airplane journey. As ever, I am impressed by the arid conditions aloft. Most passengers can suck down a liter of water on a cross-country flight without needing to micturate. After a journey like this, I myself end up with sandpaper skin, hangover eyes, and a blood-spewing nose.

I would think there might be some competitive advantage for an airline that could offer customers something better than the Gobi in the sky. I would also think flight crews would be willing to bargain through their unions to have working conditions that don’t leave them looking like Imhotep.

Why hasn’t this problem been solved, for example through strategically-placed atomizers? I suspect the answer is weight. Water is 8 pounds per gallon, and the fuel to carry that extra weight is costly. I suppose somewhere in the airline industry there is a green eyeshade type who has figured out that sucking the water out of all the passengers actually lightens the plane and thereby saves fuel.

But still…aaacck, water, water, please, water…

Comments

  1. Susan Paxton says

    Airliners are dry inside to prevent corrosion. Supposedly the new 787 can handle more interior humidity because the fuselage is composite, not aluminum.

    • larry birnbaum says

      To elaborate just a little, from what I understand, water in the cabin air has a tendency to condense on the interior of the fuselage because it’s so cold.

  2. Altoid says

    Also, cabin altitude is much higher than we might think; I don’t recall exactly but believe it’s something on the order of 8000 feet. That’s positively Andean for most of us– higher than places like Mexico City where travelers get altitude sickness– but it’s what metal fuselages can handle. It seems likely that air that thin just can’t hold the amount of moisture for a given volume that lowlanders are used to. Not that cabin air isn’t dry for most of us; I just don’t know how much humidity is possible at those low pressures.

  3. thomas says

    @Altoid. The air doesn’t have to ‘hold’ the water: the partial pressures of different gases are pretty much independent and you can have water vapour present even in the complete absence of other gases. There’s no difficulty in principle in having high humidity at low pressure, and the amount of water needed in the air to get, say, 70% relative humidity is almost identical at sea level of 8000ft pressure.

    The problem is that the outside air is very dry and cold, so either pumping outside air in, or allowing inside air to come into contact with the plane’s skin will cause humidity to fall. In the latter case, the water will come out as condensation, which as Susan Paxton says, is not a good thing.

  4. John Casey says

    Cabin air comes from the outside atmosphere, via the compressor sections of the engines and the air conditioning packs. The result is a very dry (under 5% relative humidity) cabin air, which is replaced every 3 to 5 minutes. I’ve not the energy or inclination to work out how much water would be required to humidify the cabin to, say, 50%, but it would have to be repeated 12 to 20 times an hour.

    • says

      If you were going to do something like this, running condensers and evaporators in line with the heat exchange (to recover moisture from outgoing air and return it to incoming air) wouldn’t be a big deal. And if you want a source of water, remember that every gallon of jet fuel burned leads to roughly 3 quarts of water vapor in the exhaust, hence contrails. Obviously you can’t capture all of that, but even a little would be way more than a plane needs.

      But all that would be expensive, and no one trusts airlines enough to be willing to trade higher cost for better conditions.

  5. Jean says

    Keith, I think your fellow passengers would be delighted if you were to bring on board an empty spray bottle, fill it with water during the flight, and periodically spritz yourself and your neighbors. Make sure to get it into their eyes and nostrils.

    • Bostonian in Brooklyn says

      Kind suggestion but the water would evaporate so quickly. Better to cover yourself with a preventative coat of oil. Do it before going through security since I’m not sure you can take enough with you.

  6. Jean says

    Interesting, Bostonian. If this became de rigueur, large numbers of slick passengers could presumably squeeze into smaller seats. This might produce a fourth tier of travel, safflower class, toward the back.

  7. A Dry Passenger says

    This ten-year old article from The Economist describes a system that might help: http://www.economist.com/node/655691

    Of course, it’s a ten-year old article, and it’s not like airlines have *more* money to spend on passenger comfort then they did before 9/11. The company mentioned in the article is still around: http://ctt.se/thezonaldryingsystem___215.aspx, but I do notice that the customer list doesn’t have a lot of U.S.-based airlines on it: http://ctt.se/customers___290.aspx