Re: Why wet clothes hung up can dry on a cold day

Stephanie,

The reason why wet clothes will dry even on cold days has to do with the
amount of water that air can hold at a certain temperature (VAPOR CONTENT). 
HUMIDITY is the measurement of the vapor content of air.

The capacity of air to hold vapor (water) varies with the temperature of 
the air.  As the temperature goes up, the capacity increases sharply.  For
example, at 0 degrees Centigrade (C) (32 F), air can hold 3.8 grams of 
water per kilogram of air. At 10 C (50F), it can hold twice as much and
 at 30 C (86F) it can hold nearly 8 times as much water vapor.  
Therefore, even though the air temp is cold,your laundry will still dry 
because the air around it still has the ability to hold water vapor.

One measurement of water vapor in air is called RELATIVE HUMIDITY.  It is 
expressed as a percentage, the higher the number, the nearer the air is
to being SATURATED (unable to take on more water vapor).  It is a ratio of 
the amount of ACTUAL water vapor in the air to what the air COULD hold
at a given temperature.  This is seen a lot in weather forcasts.  The 
relative humidity also relates to how "comfortable" you feel.  For example,
let us say in Florida it is 32 C (90F) with a relative humidity of 88%.
And it is the same air temperature in Minnesota with a relative humidity
of 50%.  Which do you think would be more comfortable?  Minnesota would
be a good guess.  This is because you feel comfortable as sweat you
perspire evaporates and cools your body in hot weather.  If the relative 
humidity is 88% in Florida, that is closer to the saturation capacity 
(100%) then 50% is in Minnesota.  So the air in Minnesota is capable of
still holding more water, allowing your sweat to evaporate and cool you, 
while in Florida you just get wet, the air cannot hold much more water
and therefore your body sends out more and more sweat, but it does not 
evaporate as fast, leaving you feeling miserable.

So, as you can see, laundry drying in cold weather is still possible
because it has to do with the ability of the air to hold water at any
temperature.  You could reverse your question and ask why a wet shirt
does not dry in a hot and humid climate as fast as you would think it
should.  The answer would still incorporate the fact of how much water is
present in the air already.

Hope this helps.
Ted