Cooling towers are lean and simple machines aimed to cool down water employed in industrial production processes of any kind. These are simple machines because the only component moving is the electrical fan, and the cooling process is achieved through a direct air/water contact heat exchange, without exchange pipes.
The water to be cooled enters in direct contact with the air in the cooling tower, allowing the water to be cooled at a lower temperature compared to the environmental air temperature.
This is achieved thanks to the latent heat of vaporization that brings a wind chill effect, taking advantage of the amount of water that evaporates in direct contact with air, removing calories. The amount of heat removed by water’s evaporation is a relevant amount, called latent heat of vaporization, and is equal to about 550-600 kilocalories per kg of water evaporated.
And so, a cooling tower is a machine that allows to cool water in a very efficient way with a contained energy consumption. On the opposite, there is a consumption of water, dissipated due to evaporation, that must be reintegrated in the circuit in a greater quantity than the quantity of water dissipated, in order to dilute the concentration of salts obtained as a consequence of the evaporative process.
The reference temperature for the cooling potential that can be achieved in a cooling tower is the wet bulb temperature, that is the environmental temperature measured with a thermometer with a moist bulb. Usually, wet bulb temperature in a city like Milan, for example, is 26° C in the worse conditions, in July, when ambient temperature rises up to 35-36° C. In these conditions, the wet bulb temperature is 10° C lower than environmental temperature, so that it’s possibile to cool down water at a temperature 3-4° C higher than wet bulb temperature, depending on the design and sizing of the cooling tower.