subject about " DEW POINT "
writer aceaircomp
dateof_write 2014-09-15
view_count 1113
    " DEW POINT "
The dew point is the temperature at which the water vapor in air at constant
barometric pressure condenses into liquid water at the same rate which it
evaporates. At temperatures below the dew point, water will leave the air.  
The condensed water is called dew when it forms on a solid surface.
The dew point is a water-to-air saturation temperature. The dew point is
associated with relative humidity.
A high relative humidity indicates that the dew point is closer to the current
air temperature. Relative humidity of 100% indicates the dew point is equal 
to the current temperature and that the air is maximally saturated with water.
When the moisture content remains constant and temperature increases,
relative humidity decreases.

The most common measurement of water content in compressed air is dew point.
Pressure dew point is always stated as a temperature at which dew begins to form.
compression  expansion of air affects its dew point. Genarally, compression
increases dew point and expansion lowers dew point. For an example, compressed 
air at 14 kg/cm2 the pressure dew point is -40℃ @14kg/cm2.  If the pressure is
 reduced to 7kg/cm2, the pressure dew point will fall to -45℃ @7kg/cm2.
For this reason, the phrase pressure dew point(PDP) is commonly used.  

This term usually refers to the dew point of compressed air at full line pressure.  

Many industrial users of compreesed air specify a pressure dew point -40℃ at line
pressure. This is especially so in process industries, facilities where air lines will  

be exposed to cold ambient air and systems where compressed air interacts with  

sensitive instruments and processes.