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.

Centrifugal Pump

Centrifugal Pump

Fluid flows in axially and leaves radially outward i.e. in centrifugal direction , hence the name Centrifugal pump

At the eye of impeller partial vacuum is created and due to atmospheric pressure at the suction side, pressure difference is created due to which fluid flows.

• Fluid enters pump (suction side) ---> rotating impeller pushes the liquid increasing velocity ---> liquid is discharged (discharging side) .

• Mechanical Energy (motor) ---> Kinetic Energy (fluid) --> Potential Energy

( The impeller provides more Kinetic energy to the fluid. This Kinetic energy decreases as it moves up giving rise to Potential energy (head). KE decreases due to pump casing which slows down the

fluid due to resistance. )

HEAD : The maximum height straight up, the fluid can travel. It is a function of outer dia. of Impeller & motor speed.

Pump Head + Suction Head = Discharge Head .

Typical properties of centrifugal pump : ( reason why it is widely used )

• constant head


• varying flow


• can handle huge amount of fluid at a time


• suitable for LOW viscous fluids.


• high speed flow.