超临界CO2在非均匀热流边界高温气冷壁内的流动传热机理研究

The application of superciritical carbon dioxide Brayton cylce in thermal power will increase the power generation efficiency, which has a far-reaching significance for China on the energy conservation and emission reduction. Compared with conventional steam boilers, the fluid temperature in the heating surfaces of supercritical CO2 boiler is higher, almost approaching the upper temperature limit of the tube material. As a result, even a modest heat transfer deterioration or unevenness can lead to the overheating of tube materials, directly jeopardizing the unit safety. However, the studies on heat transfer mechanisms of supercritical CO2 in heating surfaces of supercritical CO2 boiler are limited. The heating surfaces of the supercritical CO2 boiler has the characteristics of high temperature, large mass flux, un-uniformly distributed heat flux and high requirement for uniform heat transfer. Aimed at these characteristics, this project will be devoted to following studies by theoretical analysis, experiments and numerical simulations. Firstly, the action mechanisms of buoyancy effect, acceleration effect and secondary flow on heat transfer will be studied and revealed. And then the complete and accurate heat transfer correlation will be constructed considering the action mechanisms mentioned above. Finally, the coupled heat transfer model will be constructed based on experimental results and the understanding of the heat transfer mechanisms, revealing the whole heat transfer characteristics of the supercritical CO2 boiler. The achievement of this project will provide theoretical basis and technical support for the design and operation of supercritical CO2 boiler.

超临界CO2布雷顿循环在火力发电中的应用能够提高火力发电的效率，对我国节能减排具有深远的意义。与蒸汽锅炉相比，超临界CO2锅炉气冷壁内工质温度更高，接近材料的使用温度上限，气冷壁内微小的传热恶化或传热不均都可能导致壁面超温，危及机组的安全。但是目前国内外对超临界CO2工质在锅炉气冷壁的复杂边界条件和高温高压状态下的流动传热机理认识尚有不足。本项目将针对超临界CO2锅炉气冷壁所具有的高参数、大流量、非均匀热流边界以及高传热均匀性要求等特点，通过理论分析、实验和数值模拟的方法，重点研究浮力效应、加速效应和二次流动对管内超临界CO2流动传热的作用机理和影响规律，建立准确可靠的传热关联式模型，进而构建考虑了燃料化学能释放过程的气冷壁耦合传热模型，揭示超临界CO2锅炉的整体传热特性，为我国超临界CO2锅炉的设计和安全运行提供坚实的理论基础和技术支撑。

超临界CO2布雷顿循环具有高效、紧凑、灵活性好等优势，在火电、核电、光热、余热利用等领域具有广阔的应用前景。超临界CO2布雷顿循环高效的主要原因是其相对较高的平均吸热温度，因而超临界CO2锅炉气冷壁内工质温度更高，接近材料的使用温度上限，气冷壁内微小的传热恶化或传热不均都可能导致壁面超温，危及机组的安全。目前国内外对超临界CO2工质在锅炉气冷壁的复杂边界条件和高温高压状态下的流动传热机理认识尚有不足。本项目通过实验和数值模拟方法，分析主要运行参数对流动传热的影响，以及壁面温度相应变化规律，揭示管内浮力效应、加速效应和二次流动对传热的作用机理。对非均匀热流密度条件下光管内的微观流动传热特点进行理论分析，提出表征圆管内壁面热流密度不均匀性的无量纲参数—不均匀性指数，基于提出的无量纲参数修正传热关联式模型。在平台20MWth的超临界CO2锅炉上开展管屏内外侧的耦合传热实验，研究炉内的火焰辐射、壁面温度分布和管屏内的工质参数的变化规律。然后在实验数据的基础上构建从火焰辐射到管屏内工质吸热的耦合传热模型，然后用这个耦合传热模型系统研究各种可变参数对超临界CO2锅炉传热性能的影响规律。本项目的研究成果为我国超临界CO2锅炉的设计和安全运行提供坚实的理论基础和技术支撑。