Determination of Air Humidity

The humidity of air can be measured by either the dewpoint of the air or its wet bulb temperature. 

Dewpoint means the temperature of saturated water vapor that has the same vapor pressure as the humid air in question. When the total pressure is constant, the constant vapor pressure means the same as the humidity x. In other words, dewpoint is the temperature of saturated air that has the same humidity as the air being considered. 

By cooling a certain surface so cold that water starts condensing on it and measuring that temperature, the dewpoint can be measured. Combining this with the measurement of the dry bulb temperature, the state of air can be defined. 

The air pressure ui a room is 9.S0 mbar, the temperature is 20 C, and the relative humidity (p = 40%. Define the dewpoint of the room. 

The total pressure thus has no importance. If this result is. sought from a Mollier diagram by finding the intersection of the humidity line (jr = humidity of air = constant) and the saturation curve, which gives the dewpoint temperature, a diagram constructed for a pressure of 9.S0 mbar should be used. A decent ap-proximation can be found from a diagram constructed for pressure p 1 bar. 

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