Molal humidity

The humidity term and such derivatives as relative humidity and molal humid volume were developed for the air—water system. Use is generally restricted to that system. These terms have also been used for other vapor—noncondensable gas phases. 

Thus, a measurement of the wet-bulb temperature, and the temperature T, allows the molal humidity, Y, to be calculated because is known. 

The use of molal humidity as the mass-transfer driving force is conventional and convenient because of the development of humidity data for, especially, the air—water system. The mass-transfer coefficient must be expressed in consistent units. 

If equilibrium has not been reached between a mixture of components, the condition is referred to as partial saturation. At partial saturation the gas mixture obeys real gas laws. There are several ways to express the concentration of a vapor in a mixture of gases. Most often, weight or mole fraction is used. Other definitions are relative saturation (relative humidity), molal saturation (molal humidity) and absolute saturation (absolute humidity). 

Humid air at 75°C, 1.1 bar, and 30% relative humidity is fed into a process unit at a rate of 1000 m /h. Determine (1) the molar flow rates of water, dry air, and oxygen entering the process unit, (2) the molal humidity, absolute humidity, and percentage humidity of the air, and (3) the dew point. 

The latest weather report includes the following statement The temperature is 78°F, barometric pressure is 29.9 inches, and the relative humidity is 87%." From this information, estimate the mole fraction of water in the air and the dew point ( F), molal humidity, absolute humidity, and percentage humidity of the air. 

Notice that, unlike the absolute humdidity, the absolute molal humidity is independ-ent of the identity of the gas. ... 

A mixture of nitrogen and acetone vapor at 800 mmHg total pressure, 25 C, has a percentage saturation of 80%. Calculate (u) the absolute molal humidity, (h) the absolute humidity, kg acetone/kg nitrogen, (c) the partial pressure of acetone, (d) the relative humidity, (e) the volume percent acetone, and (/) the dew point. 

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