Application of Psychrometric Chart

The left-hand scale gives the enthalpy per pound of dry air of a saturated air-water vapor mixture. The enthalpy of the wet air (in Btu/lb dry air) is actually the following  

There are alternate methods available for computing enthalpy values [1,2]. For our specific system we could expand Equation 5.2 to the following  

Develop a simple expression for the humid volume of moist air. 

Humid volume is defined as the volume of 1 lb of dry air plus the volume of water vapor in the air. Hence, 

A cooling tower operation is designed without any recycle stream. Approximately 700,000 lb/hr of hot process water at 140°F is to be cooled and returned to the process operation. Moist air is used as the cooling medium and is fed at a rate of 5.5 X 106 ft3/hr. The dry- and wet-bulb temperatures of the incoming air are 80°F and 60°F, respectively. The air leaves the tower with an estimated wet-bulb temperature of 95°F and a dry-bulb temperature of 100°F. Estimate the temperature of the water returned to the process operation. 

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