On 8 Oct 2008 06:48:04 -0400,
wrote:

Kenneth wrote:

I might try aiming some sort of space heater at the glass
for a while before doing the repair.

Even heating it slightly would lower the level of humidity
between the panes, and that would, in turn, lower the
temperature at which you would see condensation.

Heating air lowers the RH but doesn't change the absolute moisture content,
so the air would have the same dew point after it cooled.

We might dry the air by running a tube from a dessicant box to the hole
and cycling the space heater every half hour for a few hours to pump air
out and back into the window cavity.

Nick

Hi Nick,

No Physicist I, but at first, I thought, "Of course... He's
absolutely right."

Then, on further reflection, (though I certainly may be
wrong) I came to see it differently:

The window used to be a closed vessel (and were that to
continue, your comment would, I believe, be correct.)

But now, it is an open vessel (the bb hole.)

Consider the analogy (though far more extreme) to a clothes
drier:

It heats the air in the drum, the RH goes down, the water in
the clothes is drawn to the air, and that moist air (with
the water it carries) is expelled by a fan via the duct.

It would appear to me that much the same thing would happen
in the case of the window:

A space heater (or some such) heats the glass of the window,
and after a few minutes, heats the air enclosed. As that air
warms, at least two things happen. First, as you say, its RH
drops. But in addition to that, it expands, expelling some
of that air via the bb hole, and with it, the moisture it
carries.

It seems to me that over time (and let's remember that the
volume of air in the window is extremely low) both the RH,
and the absolute humidity of the air in the window would
drop.

Then, when the epoxy seals the hole (while the window is
still warm) the AH within would be lower than the
surrounding environment thus lowering the temperature at
which condensation would be visible.

Might I have that right?

All the best,
--
Kenneth

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