Cryogenic refrigerating system

A multi-stage mixed-refrigerant type cryogenic refrigerating system including a compressor 1 for compressing a mixed-refrigerant drawn thereinto, an oil separator 10 for separating oil contained in the refrigerant compressed by the compressor, a condenser 2 for liquefying refrigerant vapor discharged from the oil separator, a heat exchanger 3 for heating evaporated refrigerant vapor introduced after circulating through a low-temperature side refrigeration cycle to be further evaporated and for supercooling the refrigerant condensed by the condenser 2, a first gas/liquid separator 4a for separating the supercooled mixed-refrigerant into a liquid refrigerant and a gaseous refrigerant, and a final evaporator for evaporating the refrigerant to be returned to the compressor 1, the refrigerating system further comprising:

• a plurality of expansion/suction apparatuses connected with one another in series,
• wherein each expansion/suction apparatus is constructed such that a liquid mixed-refrigerant from the first gas/liquid separator 4a passes through an expansion device 8a and is then injected from an injection nozzle 7a installed on a side end of an evaporated refrigerant carrying tube 6a into an outer tube of a double tube so that the injected refrigerant is evaporated while flowing downwardly and then flows into an evaporated refrigerant carrying tube 6 on a high temperature side, and a gaseous mixed-refrigerant discharged from the first gas/liquid separator 4a flows upwardly through an inner tube for the condensed refrigerant of the double tube 5a to be condensed and is then introduced into a second gas/liquid separator 4b;
• and
• wherein the refrigerant condensed by passing through a final expansion/suction apparatus D is introduced into a fifth expansion device 8e through a heat exchanger disposed below the final evaporator, the refrigerant introduced into the evaporator 14 is evaporated, and the completely evaporated refrigerant is returned to the compressor 1 through a tube for the evaporated refrigerant communicating with the evaporated refrigerant carrying tube,
• whereby a refrigerant circuit of the refrigerating system is formed.