I can confirm that I repeated the calculation and got a number of 28 grams per hour (using your flow rate of dry air). This is comparable to your answer.
However the watts needed per my calc was about 80. Not that it matters, but we can compare our calcs sometime.
Even if you start with zero humidity air, the water that people are losing is going into the air. So as the passengers are getting dehydrated, the air in the plane is getting hydrated. Planes are sealed, so this water in the air isn’t being lost. So there must be an equilibrium point when people stop losing water into the air. Of course that point may be low enough that people die before reaching it.
I am not sure this is true. I think air from the jet engines (after the compression stages) is added to keep the cabin pressurized. (After chilling of course).
I have the distinct ear pain whenever the pilot “idles” the engine before landing, thereby reducing the cabin pressure.
ETA simulpost w @am77494 just above.
And that’s where you’re wrong. Planes are not sealed. You get 100% all new air from the outside every 5 minutes or so. More like 3 minutes if the recirculation systems are off. Airplanes have vastly MORE fresh air than office buildings or stores do or your house has.
The system is designed that way for many reasons, but smoke removal is one of the biggies. We need to keep you alive for 10-15 minutes to find a place to land despite having a smoky fire on board. That implies a need to flush a hurricane of new air into, through, and back out of the cabin.
The flow of air in and out is carefully metered to ensure we can keep the tube several PSI above the outside atmosphere pressure. But that doesn’t mean no air goes out. It just means air comes in at the same rate it goes out.
[quote=“Little_Nemo, post:62, topic:933009”]Of course that point may be low enough that people die before reaching it.
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The very high air exchange rate on a passenger jet has already been addressed, but this point caught my interest.
According to a psychrometric chart, the moisture content of air at 20C and 100% RH is 14.76 grams of water per kilogram of dry air. This air has a density of 1.194 kg/m^3. If your bedroom is 4 meters x 4 meters x 3 meters, that’s 48 m^3 of air. You could fully humidify that air with just 834 grams of water, less than a liter; you’d be thirsty, but not dead. Based on earlier calcs, it would take one person about 24 hours of respiration in the room to achieve this (this disregards any water loss due to perspiration).
I’m not sure how to estimate one passenger’s share of cabin volume in a jet, but I’ll wager it’s much less than 48 m^3; I suspect a sealed, full cabin would be extremely humid (and gross) in a relatively short time. You wouldn’t be dead, but you might wish you were.
Okay, I stand corrected. I had always thought airliners were a relatively sealed environment.