跨临界循环

跨临界循环（transcritical cycle）是工作流体在亚临界及超临界状态之间工作的热力学循环。

针对将热能转为机械能的热机，工作流体在压缩阶段维持液态，在膨胀阶段为气态。超超临界（ultrasupercritical）蒸气的朗肯循环是从化石燃料发电的火力发电厂中广泛使用的跨临界循环，以水为工作流体^[1]。其他发电应用中常用到的跨临界循环是有机朗肯循环（英语：organic Rankine cycle）^[2]，适用于低温的热源，例如地热能^[3]、余热回收装置（英语：waste heat recovery unit）^[4]或废弃物转制能源的热源^[5]。和亚临界循环比较起来，跨临界循环在定义上就可以利用较高的压力比（英语：Overall pressure ratio），此一特性下，针对大多数的工作流体，也会有较高的热效率。超临界循环也是一种可能可以替代跨临界循环的方案。但跨临界循环可以达到较高的比功，因为压缩功的相对重要性有限^[6]。这证明了跨临界循环在以以最小支出（以压缩工作流体需耗费的能量计算）产出最大功率（以每一个循环的比功来计算）此目的上有很大的潜力。

在超临界循环（supercritical cycle）中，高压力及低压力都大于工作流体的临界压力。而在跨临界循环中，只有高压力大于临界压力，低压力会小于临界压力。在冷冻的跨临界循环应用中，越来越多会用二氧化碳CO₂作为制冷剂^{[7][8][9][10]}

参考资料

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