Heat exchanger is the general name for any device that passes the heat of a hot fluid through a wall to a cold fluid. The evaporator (refrigerant–air) and condenser (refrigerant–air) of the refrigeration cycle belong to this class. For refrigerant–water exchange plate heat exchangers (thin stainless plates) are used, for refrigerant–water or water–water shell-and-tube exchangers, and for refrigerant–refrigerant coaxial (tube-in-tube) exchangers.
Its main uses in refrigeration: chiller evaporator and condenser, milk coolers, heat recovery (producing hot water from compressor discharge gas), the "cascade" exchanger between the two circuits of a cascade system, the liquid–suction line heat exchanger (which raises capacity by subcooling the liquid and superheating the suction) and glycol circuits.
Selection is based on capacity, inlet and outlet temperatures on both sides (logarithmic mean temperature difference), flow rate and pressure drop. Plate heat exchangers give high capacity in a small volume but are sensitive to fouling and freezing; glycol concentration and flow control must not be neglected.