"Dan Luke" wrote in message
...

"J. Severyn" wrote:
So you may have part of the numbers on your side, you did not correctly
model the problem, and therefore your conclusions are probably incorrect.
Go back and do the problem correctly.

I believe I adequately showed that the amount of water present in 20 gal.
of air under extreme conditions is small, and that the amount that would
actually condense is smaller still. If you believe tank respiration will
substantially increase water condensed out of 20 gallons of air, why don't
you provide calculations showing that?

--
Dan
C172RG at BFM

OK. I'll use your own numbers and assume they are correct.

"There's not enough water in 20 gallons of air to matter.

How much water is there? In *extremely* wet conditions (saturated air
at 20 deg. C) there are only 14.7 g/kg of water in the air. A cubic
foot of air at SLP weighs about 34 grams at 20 C. 10 gallons is ~27 cu.
ft., so that gives about 900 g. of air and about 14 g. of water. Not a
problem.

--
Dan
C172RG at BFM"

You did not provide adequate or even convincing evidence that model the
problem.

If the air in the tank is exchanged 10 times over a few weeks (not
unreasonable due to temperature, barometric pressure changes and local
wind), the amount of water starts adding up. The water droplets on the
inside surface will get caught in the fuel as they drip or slowly flow into
the fuel. They will flow to the bottom of the tank and not evaporate as they
are covered with fuel.

In windy conditions, the air can exchange many more than 10 times. Most
aircraft have several fuel vents and many high-wingers connect the top of
the tanks to assure fuel delivery. The multiple vents allow lots of air
exchange if the plane is tied down outside with differences in pressure at
the different vents due to placement and wind.

So let's use your numbers....times 100 or more. 1.4 Kg of water (or more)
is a significant amount.

John Severyn
@KLVK