Malcolm,
Let's talk about what causes condensation. When the surface temperature of
the glass in your windshield is equal to or lower than the dew point
temperature of the air in front of the glass, moisture will condense from
the air onto the glass surface. (When the surface temperature is exactly
equal to the dew point temperature of the air, that's 100% relative humidity
and is the point at which condensation will just begin to occur.) The fact
that you had a thick layer of condensation on the windshield surface
indicates that the surface temperature of the glass was well below the dew
point of the air.
Was the condensation on the inside of the glass or the outside? If on the
inside, there may have been some moisture trapped in your heater. When you
turned it on, probably for the first time this year, it condensed out
temporarily on the glass surface. If the condensation was on the outside,
you probably hit a pocket of fog (saturated air), and the glass surface
temperature was below the dew point temperature of the air. Then, you
either drove out of the fog pocket, or the heater by that time warmed up the
glass temperature so that it was above the air dew point temperature.
I used to lecture on this subject, and I thank you for the opportunity to
expound.
Sumner Weisman
The Guru of Dew
62 TR3B
W1VIV
Date: Thu, 5 Aug 1999 22:13:46 -0700 (PDT)
From: Malcolm Walker <walker05@camosun.bc.ca>
Subject: Strange weather phenomenon?
While driving home tonight from a good game of badminton at the Y, had a
strange thing happen- the windshield fogged up. Both sides, right across,
to the point where I couldn't see through it! Luckily it's a small car
and I am a tall guy- stuck my head out sideways (40 MPH sure gets fast)
and drove on (much slower)
I had just turned on the heater blower to warm up my hands a bit. I was
also changing altitude. However, this hasn't happened to me before, in
any of my other cars- although then again, I haven't had a convertible
before!
Then, as quickly as it had fogged up, it cleared. (The heater was still
on). I didn't notice any fog outside the car, although we are
experiencing some odd weather (thunderstorms, fog).
Can anyone explain? No moisure appeared to have vented from the engine-
the overflow tank was dry, no hoses split, engine looked fine (when I got
home) Did I just release a long-incarcerated slice of Coventry from
somewhere within the bowels of the car?
-Malcolm
* There is a FAQ for this list! Its new home is:
http://www.islandnet.com/~walker05/triumph/trfaq.htm
|