跨臨界循環

跨臨界循環（transcritical cycle）是工作流體在亞臨界及超臨界狀態之間工作的熱力學循環。

針對將熱能轉為機械能的熱機，工作流體在壓縮階段維持液態，在膨脹階段為氣態。超超臨界（ultrasupercritical）蒸氣的朗肯循環是從化石燃料發電的火力發電廠中廣泛使用的跨臨界循環，以水為工作流體^[1]。其他發電應用中常用到的跨臨界循環是有機朗肯循環（英語：organic Rankine cycle）^[2]，適用於低溫的熱源，例如地熱能^[3]、餘熱回收裝置（英語：waste heat recovery unit）^[4]或廢棄物轉製能源的熱源^[5]。和亞臨界循環比較起來，跨臨界循環在定義上就可以利用較高的壓力比（英語：Overall pressure ratio），此一特性下，針對大多數的工作流體，也會有較高的熱效率。超臨界循環也是一種可能可以替代跨臨界循環的方案。但跨臨界循環可以達到較高的比功，因為壓縮功的相對重要性有限^[6]。這證明了跨臨界循環在以以最小支出（以壓縮工作流體需耗費的能量計算）產出最大功率（以每一個循環的比功來計算）此目的上有很大的潛力。

在超臨界循環（supercritical cycle）中，高壓力及低壓力都大於工作流體的臨界壓力。而在跨臨界循環中，只有高壓力大於臨界壓力，低壓力會小於臨界壓力。在冷凍的跨臨界循環應用中，越來越多會用二氧化碳CO₂作為製冷劑^{[7][8][9][10]}

參考資料

1. Tominaga. Advances in Steam Turbines for Modern Power Plants. Elsevier. 2017: 41. ISBN 978-0-08-100314-5.
2. Yu, Chao; Xu, Jinliang; Sun, Yasong. Transcritical pressure Organic Rankine Cycle (ORC) analysis based on the integrated-average temperature difference in evaporators. Applied Thermal Engineering. September 2015, 88: 2–13. doi:10.1016/j.applthermaleng.2014.11.031.
3. Hassani Mokarram, N.; Mosaffa, A. H. Investigation of the thermoeconomic improvement of integrating enhanced geothermal single flash with transcritical organic Rankine cycle. Energy Conversion and Management. June 2020, 213: 112831. S2CID 218783771. doi:10.1016/j.enconman.2020.112831.
4. Lecompte, Steven; Ntavou, Erika; Tchanche, Bertrand; Kosmadakis, George; Pillai, Aditya; Manolakos, Dimitris; De Paepe, Michel. Review of Experimental Research on Supercritical and Transcritical Thermodynamic Cycles Designed for Heat Recovery Application. Applied Sciences. 2019-06-25, 9 (12): 2571. doi:10.3390/app9122571 .
5. Behzadi, Amirmohammad; Gholamian, Ehsan; Houshfar, Ehsan; Habibollahzade, Ali. Multi-objective optimization and exergoeconomic analysis of waste heat recovery from Tehran's waste-to-energy plant integrated with an ORC unit. Energy. October 2018, 160: 1055–1068. S2CID 115970056. doi:10.1016/j.energy.2018.07.074.
6. Oyewunmi, Oyeniyi A.; Ferré-Serres, Simó; Lecompte, Steven; van den Broek, Martijn; De Paepe, Michel; Markides, Christos N. An Assessment of Subcritical and Trans-critical Organic Rankine Cycles for Waste-heat Recovery. Energy Procedia. May 2017, 105: 1870–1876. doi:10.1016/j.egypro.2017.03.548.
7. Dai, Baomin; Liu, Shengchun; Li, Hailong; Sun, Zhili; Song, Mengjie; Yang, Qianru; Ma, Yitai. Energetic performance of transcritical CO2 refrigeration cycles with mechanical subcooling using zeotropic mixture as refrigerant. Energy. May 2018, 150: 205–221. doi:10.1016/j.energy.2018.02.111.
8. Baheta, Aklilu Tesfamichael; Hassan, Suhaimi; Reduan, Allya Radzihan B.; Woldeyohannes, Abraham D. Performance Investigation of Transcritical Carbon Dioxide Refrigeration Cycle. Procedia CIRP. 2015, 26: 482–485. doi:10.1016/j.procir.2015.02.084.
9. Lo Basso, Gianluigi; de Santoli, Livio; Paiolo, Romano; Losi, Claudio. The potential role of trans-critical CO2 heat pumps within a solar cooling system for building services: The hybridised system energy analysis by a dynamic simulation model. Renewable Energy. February 2021, 164: 472–490. PMC 7505099 . PMID 32982085. doi:10.1016/j.renene.2020.09.098.
10. Austin, Brian T.; Sumathy, K. Transcritical carbon dioxide heat pump systems: A review. Renewable and Sustainable Energy Reviews. October 2011, 15 (8): 4013–4029. doi:10.1016/j.rser.2011.07.021.