Cooling Tower

Cooling Tower (CT) Principle ?

CoolingTower

• To decrease the temperature of hot water entering the CT.
• Cooling by evaporation is the principle used.
• Heat transfer from Water to Air.

• High difference between Wet Bulb Temperature ( WBT ) and Dry Bulb Temperature ( DBT ) encourages more Heat Transfer ( HT ) between air and water inside the cooling tower. This is due to the fact that when WBT = DBT , air is fully saturated i.e 100% relative humidity (R.H) and no longer accepts water, thus no more HT.

• Thus more difference between WBT and DBT => low R.H. => greater capacity to hold water => effective lowering of water temperature.

• Final outlet water temperature will always be < WBT of entering air. ( suppose DBT = 30°C, WBT = 25°C find R.H from humidity chart, this implies the capacity of air to hold water i.e. hot water can maximum transfer heat till its drops to WBT of entering air )

Working of CT ?

• Hot water from HE enters cooling tower
• It is sprinkled from top with the help of nozzles
• fills are used for better Heat Transfer between air and water.
• Normally water is brought down to room temperature and is collected in the concrete basin at the bottom.
• This water is re-used again and the same process follows.
• small amount of water gets evaporated during the entire process hence make up water is used .

Types of CT

1. Natural Draft ( Hyperbolic CT ) :

• ADVANTAGES : No fans, motors or gearboxes required, usually used for large quantity of water flow.
• DISADVANTAGE : Large space required
• uses the difference between ambient air temperature and the air inside tower.
• Hot air rises upwards and cooler air is drawn inside through bottom.
• Two types :

A) Cross flow Natural Draft CT: water and air flow are perpendicular. Fill is located outside CT.

B) Counter Flow Natural Draft CT: Air is dawn up through the falling water. Fill is located inside.