Analysis of Brayton Cycle in Air-cooled Refrigeration

The air-cooled refrigeration system can provide a cold source less than 20K. It is used to control the temperature of the raft, so as to adsorb the residual gas in the chamber of the simulation chamber and increase the ultimate vacuum of the simulation chamber. The built-in cryogenic pump has the advantages of high pumping speed, no pollution, and no pollution to infrared remote sensing instruments, infrared cameras, infrared horizon instruments and other optical instruments, ensuring the cleanliness of the spacecraft.

The development of a pneumatic crucible refrigeration system is a highly complex integrated technology involving pneumatic crucible refrigeration technology, liquid nitrogen refrigeration technology, vacuum technology, heat transfer technology, and helium gas purification technology, as well as the processing of precision turbines. High-speed gas bearing processing, dynamic sealing and static sealing process, etc., should also consider the reliability and maintainability of the equipment. If there is any poor design, it will affect the overall performance of the system, so that the pressure, temperature, cooling capacity and leakage rate do not meet the design criteria, resulting in the failure of the system operation.

The design principle of air-cooled refrigeration system generally adopts Brayton cycle. The Brayton cycle has two modes, one is a cycle of a first-stage expander with liquid nitrogen precooling; the other is a cycle of a two-stage expander without liquid nitrogen precooling.

Since the space environment simulation test always needs to consume a large amount of liquid nitrogen, the supply of liquid nitrogen is relatively convenient. Therefore, when designing a 20K pneumatic crucible refrigeration system, the first method is adopted, that is, the circulation of the first-stage expander using liquid nitrogen precooling is used. . Since only one stage expander is used, the reliability of operation is improved over the second mode.

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