A reverse turbo-Brayton cycle cryocooler for ZBO storage of liquid hydrogen in space

Liquid hydrogen is a high-specific-impulse propellant which is widely used in aerospace. Hydrogen storage is a key problem in the long-distance space exploration. In recent years, zero boil-off (ZBO) storage of cryogenic propellants (LH2, LO2, LCH4) is a significant storage technology for space exploration where the cryocooler is used to achieve ZBO. However, it is difficult to achieve the large cooling capacity at 20 K in space. The reverse turbo-Brayton cycle cryocooler has the obvious advantages of large cooling capacity, low vibration, high reliability and long life which is used as the cryocooler in ZBO system. In this study, a reverse turbo-Brayton cycle cryocooler combining nitrogen and helium cycles is designed to provide the cooling capacity at 20 K and 90 K for liquid hydrogen and liquid oxygen. The nitrogen cycle in the system can provide the cooling capacity of 20 W at 90 K for liquid oxygen storage while the helium cycle in the system can provide the cooling capacity of 5 W at 20 K for liquid hydrogen storage. There are three centrifugal compressors and one expander in the nitrogen cycle. The expander is coaxial with the one of compressors which can recover the expansion work. There are four centrifugal compressors and one expander in the helium cycle. A heat exchanger is used to connect the nitrogen cycle and helium cycle. The nitrogen cycle can provide the cooling capacity for the pre-cooling of the helium cycle. In addition, the cryocooler can also provide the cooling capacity of 200 W at 90 K for liquid oxygen and 200 W at 120 K for liquid methane by the nitrogen cycle. The reverse turbo-Brayton cycle cryocooler in this study can achieve the ZBO storage of liquid hydrogen, oxygen and methane in space. This work can provide the theoretical guidance for the design of ZBO storage in the long-distance space exploration.