The liquid, after being admitted by a buoy-type expansion valve, flows through the serpentine tubes, removing heat from the medium to be cooled. Upon receiving heat from the evaporator, part of the refrigerant evaporates, forming a mixture of liquid and vapor, which, upon leaving the evaporator, is led to a liquid separator. This separator, as its name says, has the function of separating the vapor phase from the liquid phase. The refrigerant in the saturated vapor state is drawn in by the compressor while the liquid returns to the evaporator as needed. As there is liquid in contact with the entire surface of the tubes, this type of evaporator effectively uses its entire heat transfer surface, resulting in high overall heat transfer coefficients.
This type of evaporator is widely used in refrigeration systems that use ammonia as a refrigerant, but its use is limited in systems with halogenated refrigerants due to the difficulty of promoting the return of the oil to the compressor crankcase. It requires large amounts of refrigerant and also has higher initial cost.
