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Re: [PSUBS-MAILIST] Humidity control
We should probably write a white paper on this sometime since it seems
to come up once or twice every year. I always find condensation easier
to understand in terms of dew point. Simply put, and in all cases, if
the temperature falls at or below the dew point, you're going to have
condensation. You can also get a sense of the relative humidity by
comparing the current temperature against the dew point. If the air
temp is 80F and the dew point is 70F then you've got high humidity and a
sticky humid day on your hands. If the air temp is 80F and the dew
point is 45F then you have low humidity and a nice dry day on your hands.
The problem starts at the surface when the air in your submarine is
filled with the atmospheric conditions of whatever the current day is
like. Now consider that when a sub is in water the cabin air is
eventually going to reach equilibrium with the water temperature. If
the water temperature is at or below the dew point of the atmospheric
air, you can expect to have condensation issues as the air temperature
in the sub begins to drop due to water conducting heat from the cabin
through the hull.
In a high humidity situation (warm humid day, cool water temps), I think
there's a simple and cheap solution that might go a long way to
controlling condensation during the dive. By emptying the air from an
80 cubic foot scuba tank into the submarine cabin just prior to closing
the hatch, the dry air from the tank should displace enough of the humid
air in the cabin to considerably lower the dew point inside the cabin
and reduce the chance of condensation. This should be easy enough to
test without the sub even in the water by simply waiting for a humid day
and monitoring the relative humidity in the sub before and after the air
from the scuba tank fills the submarine.
For warm climates such as Florida, if you have room for the small
"cooler" air conditioner that David Bartsch was working on last year, I
think that could be an ideal solution for not only controlling heat in
the cabin but also the humidity.
Calcium Chloride is cheap and easily available, and is suppose to act as
a desiccant although I've never tried it. The southern boys out there
probably don't know about this stuff, but us northern boys usually have
plenty of it on hand for melting snow and ice in the winter.
Jon
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