Closed cycle cryogenic refrigeration system with automatic variable flow area throttling device

A closed cycle cryogenic refrigeration system using a mixed refrigerant, comprising:

• an evaporator operating in a range from 70 K to 150 K for absorbing heat from a load;
• a refrigerant compressor receiving low pressure refrigerant and compressing said refrigerant to a high pressure;
• first heat exchanger means for rejecting heat including compressor heat from said system;
• second heat exchanger means for exchanging heat between a flow of low pressure refrigerant leaving said evaporator and entering said compressor, and a flow of high pressure refrigerant leaving said first exchanger means;
• an automatic restrictor valve for receiving said high pressure refrigerant from said second heat exchanger means, and for throttling said refrigerant to reduce the pressure and temperature of said refrigerant, and for delivering said reduced temperature refrigerant to an inlet of said evaporator, said valve including:
• a first orifice for refrigerant flow therethrough to throttle said refrigerant and reduce said pressure and temperature;
• first needle means for obstructing a flow area of said first orifice;
• an actuator connected to said first needle means, said actuator being responsive to changes in temperature and moving said first needle means to reduce said first orifice flow area when said actuator temperature drops, said actuator being cooled by refrigerant flow, said first orifice flow area in operation diminishing from a start of cool-down toward a steady-state operating temperature, said first orifice flow area no longer decreasing and remaining substantially constant in a predetermined range of temperature above said steady-state operating temperature.

A restrictor valve for operation in a closed cycle cryogenic refrigeration system using a mixed refrigerant, said system operating in a range from 70 K to 150 K for absorbing heat from a load, said restrictor valve comprising:

• an inlet for receiving high pressure refrigerant;
• a first orifice for flow of high pressure refrigerant therethrough to throttle said refrigerant and reduce said pressure, said refrigerant becoming cooler as its pressure decreases;
• first needle means for obstructing a flow area of said first orifice;
• an actuator connected to first needle means, said actuator being responsive to changes in temperature and moving said first needle means to reduce said first orifice flow area when actuator temperature drops, said actuator being cooled by refrigerant flow, said first orifice flow area in operation diminishing from a start of cool-down toward a steady state operating temperature, said first orifice flow area no longer decreasing and remaining substantially constant in a predetermined range of temperature above a temperature selected as a steady-state operating temperature in said range of 70 K to 150 K.

A restrictor valve for operation in a closed cycle cryogenic refrigeration system using a mixed refrigerant, said system operating in a range from 70 K to 150 K for absorbing heat from a load, said restrictor valve comprising:

• an inlet for receiving high pressure refrigerant;
• a first orifice for flow of high pressure refrigerant therethrough to throttle said refrigerant and reduce said pressure, said refrigerant becoming cool as its pressure decreases;
• first needle means for obstructing a flow area of said first orifice;
• an actuator connected to said first needle means, said actuator being responsive to changes in temperature and moving said first needle means to reduce said first orifice flow area when actuator temperature drops, said actuator being cooled, said first orifice flow area in operation diminishing from a start of cool-down toward a steady state operating temperature, said first orifice flow area no longer decreasing and remaining substantially constant at a preselected steady-state operating temperature in said range of 70 K to 150 K.