超临界CO2回热器耦合换热特性及优化设计方法研究

Supercritical CO2 (S-CO2) Brayton cycle has the properties of high efficiency, compactness and safety, and has great potential in energy fields. The recuperator plays a crucial role on the cycle efficiency, safety and stabilization of the system. However, the studies on the coupled heat transfer characteristics and optimization design method of supercritical CO2 recuperator, in which the physical properties of working fluids vary violently, are very few. Therefore, the present project is to study the heat transfer and flow characteristics of S-CO2 and the optimization design method of recuperator with the theoretical and experimental methods based on the current research progress and the applicant’s research foundation. The transformation mechanism and distribution regularity of heat transfer enhancement and deterioration of S-CO2 under heating and cooling conditions in recuperator will be investigated, the influence mechanism of parameters distribution and flow type on the coupled heat transfer between S-CO2 and S-CO2 will be explained, the synergy mechanism and matching principle of coupled heat transfer of both fluids which interact with each other will be discussed, and the new method of coupled heat transfer enhancement with high efficiency and low resistance will be proposed. The integrated performance evaluation criterion of S-CO2 recuperator will be proposed, the complete optimization design method of S-CO2 recuperator will be established based on the segmental design of heat exchanger, and the novel compact recuperator with high efficiency and low resistance will be explored. The present project is to transform the disadvantages of violent variations of properties in the heat exchanger design to the advantages of coupled heat transfer synergy enhancement, which will establish the solid theoretical foundation and provide the key technical support for the relevant researches and applications.

超临界CO2（S-CO2）布雷顿循环以其高效紧凑安全的特性在能源领域具有广阔应用前景，回热器性能对循环效率及系统安全稳定运行至关重要，而针对物性剧烈变化的S-CO2的耦合换热特性及回热器优化设计方法的研究并不充分。因此，本项目基于现有研究进展及申请人前期研究基础，采用理论与实验相结合的方法，对回热器工况内S-CO2换热流动特性及回热器优化设计方法进行深入系统研究，揭示回热器大跨度工况内加热和冷却条件下S-CO2传热强化和恶化的转换机制与分布规律，探讨两流体相互作用与影响的耦合换热协同匹配原则与强化换热新方法。研究适用于S-CO2回热器的综合性能评价标准，结合换热器分段设计思想，建立完善的S-CO2回热器优化设计方法并开发新型高效低阻紧凑式回热器。本项目旨在将物性剧烈变化的设计不利因素转化为耦合换热协同强化的有利理论依据，为相关研究及应用奠定坚实的理论基础并提供关键技术支撑。

超临界CO2（SCO2）布雷顿循环以其高效紧凑安全的特性在能源领域具有广阔应用前景，回热器性能对循环效率及系统安全稳定运行至关重要，而针对物性剧烈变化的SCO2的传热流动特性、耦合换热特性、回热器优化设计方法等研究并不充分，存在系列亟待解决的关键问题。本项目针对存在的关键科学问题，采用理论分析、数值模拟和实验验证相结合的方法，对SCO2换热流动特性及回热器优化设计方法进行深入系统研究。首先，开展了SCO2在水平管、竖直管、直通道及多种结构通道在加热和冷却等条件下传热流动特性，以及浮力、加速度等因素对传热性能影响的研究。发现了双壁温峰值现象，并通过流动分区揭示了传热强化和恶化产生的机制及分布规律，总结出新的表征浮力效应更为精确的判定依据。其次，开展超临界CO2热冷流体两侧耦合传热强化与恶化分布规律及转换机制的研究，基于向量和矩阵分析理论提出分布匹配、协同强化的换热优化原理，在不增加或极少增加压降条件下通过改善换热区域参数分布的协同性实现传热强化，将物性变化的设计不利因素转化为强化换热的有效途径，并提出了表征变物性流体性能的广义平均温差法，具有重要的理论意义和工程价值。最后，基于传热强化新原理提出了新翼型换热结构并制作测试样机，模拟和实验结果显示相对于现有翼形结构传热性能提高而流阻有所下降，相对于最常用之字形结构传热性能相当而流阻大幅下降，综合性能达到最优，根据模拟和实验测试数据拟合出传热和压降关联式，用于该结构换热器的设计和优化，具有重要的工程应用价值。本项目发表期刊论文16篇(SCI收录14篇，EI收录2篇)，国际会议论文5篇，培养研究生3人，申请/授权国家发明专利4项，相关研究成果在国家大科学装置、上海电气等超临界CO2发电系统中进行推广和应用，获得良好的社会和经济价值。