| 摘要 |
A cascade refrigeration system includes an evaporator unit (10, 12) located adjacent a test chamber and remote from the refrigeration system. A conduit (38) carries refrigerant from the cascade refrigeration system to the evaporator unit (10, 12). The liquid refrigerant passed through an expansion valve (28) to meter the refrigerant to delivery to the evaporator unit (10, 12). Spent refrigerant exiting the evaporator unit is returned to the cascade refrigeration system by a return line (40). In order to maintain a constant liquid refrigerant flow to the expansion valve so as to enable the refrigeration system to cool the chamber as needed, liquid refrigerant is bypassed around the evaporator unit (10, 12) and to the return line (40). The bypass circuit includes a control valve (162) which selectively diverts liquid refrigerant to the return line (40) during low-demand conditions at the evaporator unit (10, 12), thus maintaining a constant supply of liquid at the expansion valve.
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