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Dehumidifiers
& Air Dryers
Actual vapor
pressure The partial pressure
exerted by the water vapor present in a parcel. Water in a
gaseous state (i.e. water vapor) exerts a pressure just
like the atmospheric air. Vapor pressure is also measured in millibars.
Dehumidification The
process of removing moisture from the air or other materials.
Desiccant A substance
such as calcium oxide or silica gel that is used as drying agent.
Dew point The
temperature air must be cooled to in order for saturation to occur,
producing water in the form of dew or condensation. The
dew point temperature assumes there is no change in the air pressure
or moisture content of the air.
Dry bulb temperature The
actual air temperature.
Evaporation The
change of liquid water into water vapor. Moisture evaporates due
to differential
vapor pressurethe larger the vapor pressure differential, the
faster the drying.
Humidistat An
instrument that indicates or controls the relative humidity of
the air.
Hygrometer An
instrument that measures atmospheric humidity.
Relative humidity
The ratio of the amount of water vapor in the air at
a specific temperature to the maximum capacity of the air at that
temperature.
Relative humidity is expressed as a percentage and can be computed
in a variety of ways. One way is to divide the actual vapor pressure
by the saturation vapor pressure and then multiply by 100 to convert
to a percent.
Saturation of air
The condition under which the amount of water vapor in
the air is the maximum possible at the existing temperature and
pressure.
Condensation or sublimation will begin if the temperature falls
or water vapor is added to the air.
Saturation vapor
pressure The maximum partial
pressure that water vapor molecules would exert if the air
were saturated with vapor at a
given temperature. Saturation vapor pressure is directly proportional
to the temperature.
Wet bulb temperature
The lowest temperature that can be obtained by evaporating
water into the air at constant pressure. Wet bulb temperatures
can be
used along with the dry bulb temperature to calculate dew point
or relative humidity.
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