“Large-scale cryogenic refrigeration equipment from the liquid helium to superfluid helium temperature zone,” a National Major Scientific Research Equipment Development Project, passed expert acceptance inspection and achievement appraisal on April 15, 2021. This shows that China is now capable of developing its own large-scale cryogenic refrigeration equipment at the liquid helium temperature (-269 ℃) kilowatt level and at the superfluid helium temperature (-271 ℃) hundred-watt level. 

Helium is a noble gas and becomes liquid at -269 ℃. When the temperature falls to -271 ℃ or more, it demonstrates a superfluid state, which exhibits many unusual properties such as zero viscosity and zero entropy. Difficulties mount exponentially when trying to realize a 1 ℃ decrease in temperature below -269 ℃ or an increase in power of one order of magnitude, thus requiring the redesign of related systems and upgrading of key components. 

A series of core technological breakthroughs were achieved in this project, including the construction and control of overall large cryogenic refrigeration equipment, and technologies related to serialized gas-bearing helium turbine expanders, large superfluid helium subatmospheric heat exchangers, large oil-injection helium screw compressors with high efficiency, centrifugal cold compressors with high stability, and large complex cryogenic refrigeration equipment integration and debugging. 

Large-scale cryogenic refrigeration equipment for the liquid helium to superfluid helium temperature zone is an indispensable core foundation for various fields, including aerospace, hydrogen storage and transportation, helium resource exploitation, and large scientific facilities. The successful development of this equipment will not only meet the nation’s high-tech development needs related to large scientific projects, aerospace engineering and helium extraction, but will also boost advanced technologies in related fields.