Vapor compression device and method

A method of operating a refrigeration system with vapor compression (10) in which an evaporator (16) removes heat from a medium that is circulated through said evaporator (16) relative heat exchange with a coil evaporator in said evaporator (16), said evaporator coil an inlet which is in fluid communication with an expansion device (18) and an outlet which is in fluid communication with a compressor (12), the method comprising: compressing a refrigerant fluid in said compressor (12); condensing said refrigerant fluid in a condenser (14) to form a condensed refrigerant fluid; expanding said fluid condensed refrigerant in said expansion device (18) to form an expanded refrigerant fluid, characterized by supplying said expanded refrigerant as a mixture of refrigerant liquid and vapor to a supply line of the evaporator (28) connecting said expansion device (18) to said inlet of the evaporator coil; converting a significant amount of the liquid component of said refrigerant mixture to vapor within said supply line of the evaporator (28), wherein the diameter and length of said supply line of the evaporator (28) facilitates the conversion, resulting from this way supplying refrigerant evaporator inlet having a substantial vapor content; convert substantially all the remaining liquid to vapor as said mixture passes through said evaporator coil, whereby an efficient heat transfer between said mixture and said medium along substantially the entire length of said coil is provided, and which frost buildup on said evaporator coil is substantially reduced.