Rankine cycles describe the operation of steam heat engines commonly found in power generation plants. In such vapour power plants, power is generated by alternatively vaporizing ng fluid (in many cases water, although refrigerants such as ammonia in a Rankine cycle follows a closed loop and is re-used constantly.

Water vapour seen billowing from power plants is evaporating cooling water, not working fluid. (NB: steam is invisible until it comes in contact with cool, saturated air, at which point it condenses and forms the white billowy clouds seen leaving cooling towers).