Having delivered its energy to the turbine, steam condensates in condenser, and getting back to water state, it flows back, via heaters, to steam generator. In condenser, the mixture is cooled by a third cooling circuit. In this latter circuit, water is cooled by air flowing from the bottom to the upper part of the cooling tower due to so-called chimney effect. The stream of air takes along water steam and small water droplets, and that is why clouds of steam form above the cooling towers.