Argon–oxygen mixtures for Joule–Thomson cryocooling at elevated altitude

•Addition of O2 to Ar makes a gainful coolant for JT cryocooling for the 90 K range.•This coolant does not freeze at high altitude (low pressure) where pure Ar does.•The JT cryocooling parameters of this mixed coolant remain very similar to pure Ar.•A test with 20% O2 coolant with a JT cooler exhibited the viability of this idea.

At high altitude where the ambient pressure is low, argon as a coolant of a Joule–Thomson cryocooler solidifies and is not able to preserve the temperature of a cooled object with the same success as by liquefied and boiling argon. Instead of other strategies of thermal storage techniques, it is proposed to add oxygen to argon so to suppress the triple point of the mixture below that of argon. An experiment with 20% oxygen mixture demonstrated that indeed a cryocooler for argon operates well with the mixture while enabling solid free higher altitude run. An analysis of pure oxygen and its mixtures with argon shows that the performance of the mixed coolant is reasonably close to that of pure argon.