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

Makeup water is supplied during cooling tower operation to compensate for water losses due to all of the following:

1. Evaporation: Cooling towers operate by using evaporation to remove heat from water. As water is evaporated into the atmosphere to cool the process fluid, there is a loss of water from the system. Makeup water is supplied to replenish the water lost through evaporation.
2. Blowdown: Blowdown is the process of removing a portion of the circulating water from the cooling tower system to control the concentration of dissolved solids and impurities. This discharged water is replaced with makeup water to maintain the desired level of water in the system.
3. Entrainment: Entrainment refers to the unintentional capture of water droplets by the exiting air stream from the cooling tower. These water droplets, carrying some of the circulating water, are lost from the system. Makeup water is needed to compensate for this loss.