Development of a Mixed-Refrigerant

We discuss in this paper the development of a mixed-refrigerant Joule-Thomson microcryocooler (MCC) to support on-chip cooling of high temperature superconducting electronics that require less than 5 mW of net refrigeration at about 80 K. Some applications include the cooling of infrared and terahertz imaging sensors that operate at about 77 K. Terahertz sensors can be used for the imaging of concealed nonmetallic weapons as well as the spectroscopic identification of chemical and biological material. The MCC is designed to deliver approximately 9 mW gross refrigeration, which yields about 3 mW of net refrigeration once losses due to the heat exchanger, conduction, radiation, and pressure drop are subtracted. The cryocooler utilizes a multicom-ponent gas mixture that is precooled to 240 K by a thermoelectric cooler. Precooling the gas mixture signifi-cantly increases the minimum isothermal enthalpy difference, which is the gross refrigeration power per unit flow. For a pressure ratio of 16:1 this enthalpy difference is about 1.43 kJ/mol for the mixed refrigerant compared with 0.15 kJ/mol for pure nitrogen. The MCC has been designed to operate at pressure ratios of 16:1 to 25:1 for a flow rate of about 6 mmol/s ( ~ 0.15 std. cm3/s)