From: Sean T. Stevenson
<cast55@telus.net>
To:
personal_submersibles@psubs.org
Sent: Wed, March 16, 2011 8:08:26
PM
Subject: Re:
[PSUBS-MAILIST] Humidity control
I would think that, with the
possible exception of very short dives, in a
small space (PSub size) the
moisture present in the surface air that gets
enclosed in the vessel is
less significant than the moisture introduced by the
occupants breath
over the course of a dive?
-Sean
On Tuesday 15 March 2011
23:00:13 you wrote:
> 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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