Progress of auto-cascade refrigeration systems performance improvement: Composition separation, shift and regulation

The current demand for wide temperature range promotes the development of mixed refrigerant throttling refrigeration technology. As a refrigeration technology using mixed refrigerants, auto-cascade refrigeration technology has a broad application prospect in the field of refrigeration and cryogenic because of its wide operating temperature range, simplicity and reliability. Although the cycle structure construction of the auto-cascade refrigeration cycle (ARC) and diversification of mixtures have received considerable progress, there are fewer reviews covering the influence factors that restrict the performance of ARC systems and providing guidelines for future development from the perspective of mixed refrigerant compositions. To bridge the gap, this paper comprehensively reviews and guidelines on the performance improvement methods of auto-cascade systems from perspective of mixed refrigerant compositions, including influence factors, research progress, research methods and technical challenges. The cycle structure construction and the factors that constrain performance improvement were summarized. It inferred that the improvement of composition separation and the modification of composition shift can improve the system performance. Then, the research on the composition separation was discussed in terms of the cycle structure modification, the separation performance of the gas-liquid separator and the separation mechanism of mixtures. The influence factors of composition shift, the composition shift characteristics and its theoretical prediction modeling are reviewed. Meanwhile, active regulation of composition concentration is a feasible measure to ensure operation safety and improve the performance of the ARC system. Finally, the technical challenges and prospects are proposed for outlining potential research directions in ARC technology.