ANS:D - all (a), (b) and (c)

Make up water is required in a cooling tower to replace the water lost by all (a), (b) and (c): evaporation, drift, blowdown, and leakage. Explanation:

1. Evaporation:
   • Water in a cooling tower is continuously evaporating as it comes into contact with the air stream and exchanges heat with it.
   • Evaporation is a natural phenomenon in cooling towers and is the primary mechanism by which heat is dissipated from the system.
   • The water lost due to evaporation needs to be replenished with make-up water to maintain the desired water level in the cooling tower basin.
2. Drift:
   • Drift refers to the small droplets of water entrained in the air stream leaving the cooling tower.
   • Despite efforts to minimize drift through the use of drift eliminators or mist eliminators, some water is inevitably lost in this manner.
   • This loss of water needs to be compensated for by adding make-up water to the cooling tower.
3. Blowdown and Leakage:
   • Blowdown refers to the intentional removal of a portion of the circulating water to control the concentration of dissolved solids and prevent scaling and fouling in the cooling system.
   • Leakage refers to unintentional losses of water from the cooling system due to leaks in pipes, fittings, or other components.
   • Both blowdown and leakage contribute to the loss of water from the cooling tower and necessitate the addition of make-up water to maintain the water balance.
4. Make-Up Water:
   • Make-up water is fresh water added to the cooling tower system to compensate for the water lost through evaporation, drift, blowdown, and leakage.
   • By adding make-up water, the water level in the cooling tower basin is maintained, ensuring proper cooling tower operation and heat dissipation.