cal65 From Hong Kong, joined May 2013, 2 posts, RR: 0 Posted (6 months 3 weeks 4 days 3 hours ago) and read 3160 times:
I have a question that people I've asked in the aviation industry haven't been able to answer. I know that vacuum toilets on commercial airlines will suck the waste into a storage tank, either centrally located in the plane or one serving that section of toilets. I'm interested in knowing how well insulated these tanks are, and what kind of temperatures we can expect the liquid inside to reach, both in high altitude and upon landing. I've read up on a patent for airplane lavatory waste storage and it spends a lot of time discussing thermal heating, so I'm positive this is an issue engineers have looked into. Obviously the design will want to prevent waste from freezing, so I know that the temperature is somewhere between 0 and cabin temperature (unless this sewage has a lower freezing temperature than water).
I'm interested in this "cold turd" situation because I'm wondering if somewhere in the discharge process at the airport, maybe we could capture some of the cold energy from the tank and use it.
On a related note, I've learned that a 747 typically carries 4 tanks totalling 1000 L for waste storage. They overdesign for the storage because if the tank fills up, no one would be able to flush again and everybody loses. Does anyone know how much waste is typically produced on a 747 flight?
I realize these are super random and literally crappy questions, but I'd really appreciate it if anyone had any insight here.
P.S. UNRELATED question: What type of water is required to wash airplane engines? De-ionized water? Can lower quality water (reclaimed water perhaps) be used for other aircraft washing needs?
LH707330 From United States of America, joined Jun 2012, 448 posts, RR: 0 Reply 1, posted (6 months 3 weeks 3 days 3 hours ago) and read 2972 times:
I'd assume the tanks are just under half full on a typical 10-hour flight. Figuring 400 passengers*300ml*3 trips to the head gets you 360 liters, and with that number of passengers you will see pretty reliable (small) fluctuations over time.
Tristarsteve From Sweden, joined Nov 2005, 3860 posts, RR: 34 Reply 6, posted (6 months 3 weeks 1 day 15 hours ago) and read 2568 times:
Quoting Tod (Reply 3): The tanks are not thermally protected.
They don't need to be.
The toilet waste tanks, and the potable water tanks are behind the sidewall and backwall of the bulk cargo hold. Air from the passenger cabin passes them on its way to the aft outflow valve. This keeps these tanks around 20 degC.
Quoting Tristarsteve (Reply 6): The toilet waste tanks, and the potable water tanks are behind the sidewall and backwall of the bulk cargo hold. Air from the passenger cabin passes them on its way to the aft outflow valve. This keeps these tanks around 20 degC.
Potable tank locations can vary.
747 have them aft of the forward cargo hold, up against the wing box.
A330 have either one or two outboard of the aft cargo hold, on the right side, forward of the cargo door in addition to one that is installed aft of the bulk cargo compartment on some versions.
Although neither has heated tanks, both models have heated distribution lines directly attached to them.
Last I heard, Monogram was installing a heated potable water tank on the new MRJ-90.
AA737-823 From United States of America, joined Mar 2000, 5547 posts, RR: 11 Reply 9, posted (6 months 2 weeks 1 day 14 hours ago) and read 1860 times:
Quoting Tod (Reply 5): In a vacuum waste system water from the potable water system is used for the toilet flush function.
But the tank is pre-charged with blue juice, just like in the old days. Otherwise, you'd have an epic bacteria issue.
On the 737, the pre-charge is six gallons.
Quoting cal65 (Thread starter): I'm interested in knowing how well insulated these tanks are, and what kind of temperatures we can expect the liquid inside to reach, both in high altitude and upon landing.
Well, residing in the aft cargo pit, the waste stays at the same temperature as the baggage. While this does get a bit chilly, it doesn't typically freeze. Even when the plane sits on the ground during turns in northern Alaska winters... no issues.
So I don't think that we'd find the use of such material as a thermal sink (recapturing the cold energy from turds, as you suggest) very useful.