Dry cooling towers operate by heat transfer through a surface that separates the working fluid from ambient air, such as in a tube to air heat exchanger, utilizing convective heat transfer. They do not use evaporation, hence the consumption of makeup water is minimal. Air Cooler or Air Cooled Heat Exchanger (ACHE) are commonly used where a reliable source of water is not available as a cooling media. Even when water is available, ACHEs are sometimes favored for economic or operational reasons. Hot process fluid enters one end of the ACHE and flows through tubes, while ambient air flows over and between the tubes, which typically have externally finned surfaces. While this is a fundamentally simple concept, maintaining optimum ACHE performance takes diligence. Dry type of cooling towers can be Forced or Induced draft.
