Research on Small-Scale Oxygen Liquefaction Using a Stirling Cryocooler

Traditional cryogenic air separation units are unsuitable for distributed, small-scale liquid oxygen production. Cryocooler-based liquefaction technology offers an alternative solution, featuring a large cooling capacity, high efficiency, a compact structure, and rapid start–stop capability. In this paper, an oxygen liquefaction system based on a high-capacity Stirling cryocooler was developed. Because the heat transfer performance of cryocoolers varies significantly across different temperature ranges, heat exchanger designs must be tailored to specific operating conditions. However, research on cold-end heat exchangers for large-capacity cryocoolers used in liquefaction systems remains limited. In the liquid oxygen temperature range, factors such as liquid film formation and incomplete condensation severely affect heat transfer performance and must be considered. In this paper, numerical simulations were performed to analyze the condensation behavior of oxygen, with particular attention paid to the matching between the heat exchange structure and the cooling capacity. Subsequently, a small-scale experimental system was constructed and tested. The successful operation of the experimental system validated the feasibility of the proposed heat exchanger design. Under the conditions of 300 K and an oxygen inlet gauge pressure of 0.45 MPa, the system achieved a liquefaction capacity of 7.4 L/h, corresponding to a cooling capacity of 787 W. The specific power consumption was 0.89 kW·h/kg, with a coefficient of performance (COP) of 0.116. This performance is competitive among small-scale cryocooler-based oxygen liquefaction systems. This study provides both theoretical and experimental support for further performance optimization and engineering application of such cryocoolers in liquid oxygen production.