WORKING PRINCIPLE OF COOLING TOWER.
The function of a cooling tower is to dissipate heat from water-cooled refrigeration, air- conditioning and industrial process systems. Water is typically the heat transfer medium used to dissipate the heat. A cooling tower uses a combination of heat and mass transfer evaporation) to cool the water flowing through the tower. Conductive heat transfer accounts for 20 to 30% of the total heat dissipated. The remaining 70 to 80% of total cooling is the result of evaporative cooling of about 1 to 2% of the recirculating water, depending on the decrease in temperature across the tower. It takes approximately 2,326,000 joules to evaporate 1 kilogram of water (1000 BTU per 1 pound of water).
If this amount of heat is extracted from 454 kilograms (1000 pounds) of water, approximately 0.45 kilogram (1 pound) of water will be evaporated and the temperature will drop 0.55 °C (1 °F). If 4.5 kilograms (10 pounds) of water are evaporated, the water temperature will drop 5.5 °c (10 °F). The water lost by evaporation is replaced with makeup water.
Water is also added to replace water lost through tower drift (loss of water from the tower as a fine mist), leaks in the system (unintentional blow down), and water discharged as intentional blow down. Water that is added to the cooling tower to replace all of these losses is known as cooling tower makeup water