What is Humidity?
Humidity is water vapor present in the atmosphere is known as Humidity.
When water vapor mixes with other gases of atmosphere, it exerts a pressure in all direction as do the other gases.
This partial Pressure exerted by vapor is known as the vapor pressure.
Saturated vapor pressure
When air contains all the moisture that it can hold to its maximum limit, it is called saturated air and the vapor pressure exerted by this air is called saturated vapor pressure.
Relative Humidity (RH)
Relative humidity represents the amount of water vapor actually present in air compared with the maximum amount of vapor can be held same air at a given temperature.
Actual quality of water vapor present in a given volume of air
RH= —————————————————————————————————- X 100
Maximum amount of water vapor the same volume of air can hold
Specific humidity is defined as the ratio of mass of water vapor to the given mass of air contacting the moisture
Thus it will be measure in grams of water vapor per kg of air.
Maximum ration = MV/Ma
MV : Mass of water vapor
Ma : Mass of dry air
Mixing ration : It is the ration of the mass of water vapor to the mass of dry air
Absolute Humidity (AH)
Absolute humidity is defined as the ratio of actual mass of water vapor present to the total volume of moist air in which it is contained.
It is measured in grams per cubic meter of air or in terms of partial pressure of water vapor in air in mbor mm mercury.
AH = Weight of water vapor / Volume of air
Measurement of humidity with different instruments is called psychometric