Direct Evaporative CoolerIn a direc

Direct Evaporative CoolerIn a direct evaporative cooler, the air stream to be cooled directly contacts the water spray or wettedmedium as shown in Figure 9.8.3(a). Evaporative pads made of wooden fibers with necessary treatmentat a thickness of 2 in., rigid and corrugated plastics, impregnated cellulose, or fiber glass all drippingwith water are wetted mediums.The direct evaporation process 12 takes place along the thermodynamic wet bulb line on the psychrometric chart. Saturation effectiveness εsat is an index that assesses the performance of a direct evaporativecooler:(9.8.6)where T, T* = temperature and thermodynamic wet bulb temperature of air stream, °F. Subscript aeindicates the entering air and al the leaving air. εsat usually varies between 0.75 and 0.95 at a water–airratio of 0.1 to 0.4.