两级蓄冷跨临界压缩 CO₂ 混合工质储能系统特性分析

In order to solve the problem of difficult condensation of high-pressure CO₂ in higher ambient temperature, a transcritical compressed CO₂-based mixture energy storage system with two-stage cold energy storage was proposed. The CO₂-based mixture via blending CO₂ and organic working medium with low boiling point was selected to improve the condensation temperature. Meanwhile, a two-stage cold energy storage system via methanol was employed to store and recycle the cold energy. Firstly, the feasible CO₂-based mixtures and the related mass fraction ranges of organic working mediums were determined by considering the environment, critical temperature, temperature glide and miscibility. Then, the system thermodynamic models were established, and the effect of several key parameters on system performance was explored, such as throttling pressure, high-pressure storage tank pressure and mass fraction of organic working medium. At the same time, the system internal energy flow was analyzed, and the exergy destruction distribution of main components was obtained. The results show that the cold energy storage medium temperature increases and the system safety is enhanced with the increase of mass fraction of the organic working mediums. Compared with pure CO₂, the round-trip efficiency and energy density of CO₂-based mixture decrease slightly. The round-trip efficiency of CO₂/R32 mixture has the maximum value of 62.29%. The energy density with CO₂/pentane mixture reaches the maximum value of 21.37