COOLING TOWERS

1                 Water in contact with air under adiabatic conditions eventually cools to the wet bulb temperature.

2                 In commercial units, 90% of saturation of the air is feasible.

                    3. Relative cooling tower size is sensitive to the difference between the exit and

                    wet bulb temperatures:
∆T (F)  5 15 25
Relative volume 2.4  1.0  0.55 

3                 Tower fill is of a highly open structure so as to minimize pressure drop, which is in standard practice a maximum of 2 in. of water.

4                 Water circulation rate is 1-4 gpm/sqft and air rates are 1300-1800 lb/(hr)(sqft) or 300-400 ft/min.

5                 Chimney-assisted natural draft towers are of hyperboloidal shapes because they have greater strength for a given thickness; a tower 250 ft high has concrete walls 5-6 in. thick. The enlarged cross section at the top aids in dispersion of. exit humid air into the atmosphere.

6                 Countercurrent induced draft towers are the most common in process industries. They are able to cool water within 2 F of the wet bulb.

7                 Evaporation losses are 1 % of the circulation for every 100 F of cooling range. Windage or drift losses of mechanical draft towers are 0.1-0.3%. Blowdown of 2.5-3.0% of the circulation is necessary to prevent excessive salt buildup.