Multiple serpentine tube heat exchanger

An evaporator for a refrigeration system having a face toward which air is directed and a back from which the air exits and comprising at least two serpentine shaped tube passageways with substantially the same cross-sectional outline arranged side-by-side so that one of said passageways is ahead of the other relative to air flow therepast and solely constitutes the face of the evaporator and said other passageway solely constitutes the back of the evaporator, said one passageway having an inlet and outlet located at one side of the evaporator, said other passageway having an inlet and outlet located at said one side of the evaporator, an inlet fitting connected to said inlet of said one passageway, a mixing chamber connected to said outlet said one passageway and to the inlet of said other passageway so that said mixing chamber is connected between said face and back of the heat exchanger, an outlet fitting connected to the outlet of said other passageway, said one passageway having an internal surface area suited to predominately liquid refrigerant flow, and said other passageway having internal area enlarging means providing substantially more internal surface area than said one passageway for effecting enhanced heat transfer with predominately gaseous refrigerant flow in said other passageway.