Water Heat Exchangers that use steam-driven turbines commonly use heat exchangers to boil water into steam. Water Heat Exchangers or similar units for producing steam from water are often called boilers or steam generators. Two-phase heat exchangers can be used to heat a liquid to boil it into a gas vapor, sometimes called boilers, or cool a vapor to condense it into a liquid called condensers, with the phase change usually occurring on the shell side. Boilers in steam engine locomotives are typically large, usually cylindrically-shaped shell-and-tube heat exchangers. Water Heat Exchangers large power plants with steam-driven turbines, shell-and-tube surface condensers are used to condense the exhaust steam exiting the turbine into condensate water which is recycled back to be turned into steam in the steam generator. Water Heat Exchangers special large heat exchangers pass heat from the primary reactor plant system to the secondary steam plant system, producing steam from water in the process. These are called steam generators. All fossil-fueled and nuclear power plants using steam-driven turbines have surface condensers to convert the exhaust steam from the turbines into condensate water for re-use.