近（超）临界区新型热力循环工质热流迁移特性的研究

近(超)临界区工质热导率、比热容、黏度等热流迁移特性奇异变化规律和机理是实现先进超(跨)临界循环系统高效安全运行的重要保障。本项目针对新型环保工质在近(超)临界区热流迁移性质突变规律及其与循环耦合机理开展研究，基于激光法和流动法热物性测试平台，发展近临界区和超临界高参数区新型工质的热导率、黏度、比热容的精确获取方法，并对烷烃、卤代烯烃、CO2及其混合物的相关物性进行测量，完善新型工质的热物性实验数据库；基于分子动力学、第一性原理等直接模拟方法，探究近临界区热物性奇异变化的分子机理，重点考虑临界跨接项的构造，建立从亚临界到超临界区域相关物性的计算模型；根据新工质精确的热物性数据，分析不同热物性对循环性能的影响规律，建立新型循环和工质性质耦合作用的热力学模型，探究超(跨)临界循环节能原理，并提出工质设计理论。本项目的研究成果对于新型动力和制冷循环以及与其适配的新型工质开发和应用具有重要的意义。

The thermophysical properties of fluids in the supercritical region as well as near the critical point are very different from those in other thermodynamic regions, which include thermal conductivity, heat capacity, and viscosity. The knowledge of the singular behavior of these properties is key issues for modern cycle systems operating efficiently and safely at extreme conditions. This project will address two main problems about alternative working fluids: 1) The fluctuations of their transport properties near the critical point; 2) The coupling mechanism of transport properties on the performances of cycle systems. First, based on the laser method and the flow method, the accurate determinations of thermal conductivity, heat capacity, and viscosity will be studied for alternative working fluids in the supercritical region and near the critical point. The thermophysical properties of alkane, halogenated olefin, CO2, and their mixtures will be measured to develop better experimental databases for the corresponding working fluids; Then, molecular dynamics simulations as well as ab initio methods will be employed to investigate the singular behavior of the considered properties and their mechanism near the critical point, which will be used to construct crossover terms near the critical point and to develop prediction models covering a wide thermodynamic range; Finally, based on the accurate thermophysical property data obtained in this project, thermodynamic models coupling modern cycles with their working fluid properties will be established, which will be utilized to analyze the effect of different thermophysical properties on cycle performances, to find the principle of energy saving for the cycle systems working in extreme conditions, and to further develop the theory of working fluid designs. In conclusion, the research outcome of this project will be significantly important to modern power cycles and refrigeration cycles as well as the R&D of alternative working fluids.