Abstract: A shell and tube type evaporator using a refrigerant and shell fluid and including a vertically positioned shell having an upper and lower end and substantially parallel tubes longitudinally disposed within the shell. The shell has inlet means near its lower end and outlet means near its upper end for passing the refrigerant through the tubes. The shell also has inlet and outlet means for passing the shell fluid through the shell. Preferably the refrigerant is ammonia and shell fluid is brine.