Heat exchangers are used to transfer heat from one medium to another. These media may be a gas, liquid, or a combination of both. The media may be separated by a solid wall to prevent mixing or may be in direct contact. Heat exchangers can improve a system’s energy efficiency by transferring heat from systems where it is not needed to other systems where it can be usefully used.
Another common use of heat exchangers is to pre-heat a cold fluid entering a heated process system using heat from hot fluid exiting the system. This reduces the energy input necessary to heat the incoming fluid to working temperature.