On Nov 28, 9:22 am, "Bill Habr" wrote:
wrote in message


Dewpoint:
The temperature to which a given air parcel** must be cooled at constant pressure in order
for equalization* to occur.

Humidity:
The ratio of the vapor pressure to the equalization* vapor pressure at a given
temperature with respect to water, usually expressed as a percentage.


Ok,
but I have some new questions:

1 - Would the above definition be for ABSOLUTE humidity, or RELATIVE
humidity? And how can we express the other in the above terms?

2- The current vapor pressure can be measured with a manometer. Are
the equalization pressures known and established for various
temperatures, say in a NIST table, and well known?

* "equalization" is usually referred to as "saturation" but "saturation" is a hold over
from an18th century understanding of science when it was thought that air was like a
liquid solution.


Have I got this right?
The equalization pressure is the pressure in a system when the
pressures from air and from water vapor are equal, and when the system
pressure decreases any beyond this point (say due to cooling) the
water vapor pressure exceeds the system pressure and water condenses?

Is this behavior different between a closed system (say a duct) and an
open system (atmosphere/weather)?

** Technically - the temperature and pressure are that of the water vapor.