基于频域法的超临界二氧化碳流动不稳定性研究

As a new concept advanced power generation system, Supercritical Carbon Dioxide Brayton Cycle owns the great development prospects, because the cycle efficiency is enough high and the relevant equipments present a smaller volume. To design and utilize the Supercritical Carbon Dioxide Brayton Cycle power generation system in a safe and efficient way, the fundamental research on the flow instabilities of supercritical carbon dioxide is necessary. However, the studies on the flow instabilities of supercritical carbon dioxide are limited, whether domestic or abroad, especially in the application of frequency domain method. It is detrimental to reveal the characteristics of the flow instabilities of supercritical carbon dioxide in depth. Hence, in the present project, based on a lot of past research experiences, a brand new regional partition method of the supercritical carbon dioxide physical properties, which is suitable for the frequency domain method, will be proposed, according to the detailed analyzation of the supercritical carbon dioxide physical properties. Then, a univariate frequency domain method calculation model and a multivariable frequency domain method calculation model will be established for the flow instabilities of supercritical carbon dioxide, and the characteristics of the flow instabilities of supercritical carbon dioxide will be studied in depth. Finally, based on lots of calculation results and somewhat data from verification experiments, the calculation correlations of boundary heat flux of the supercritical carbon dioxide flow instabilities will be obtained and the relevant stability boundary diagram will be also determined. The present research can provide theoretical basis and technical support for the design and development of the advanced power generation systems using supercritical carbon dioxide, such as Supercritical Carbon Dioxide Brayton Cycle.

超临界二氧化碳布雷顿循环发电系统是一种先进动力系统，循环效率高，设备体积小，应用前景很好。对超临界二氧化碳流动不稳定性的研究是进行该发电系统设计和应用必不可少的基础性研究工作之一。目前国内外对超临界二氧化碳流动不稳定性的认识尚有不足，研究方法的发展也相对滞后。因此，本项目拟基于前期的研究积累，从频域法入手，通过深入分析超临界二氧化碳物性变化规律，创新性地提出能够将超临界二氧化碳物性变化特点准确地反映在频域法模型中的超临界二氧化碳物性分区方法；在此基础上建立超临界二氧化碳流动不稳定性的频域法模型，进而深入分析超临界二氧化碳流动不稳定性的机理和规律；通过计算，辅以实验数据，获得拟过冷度、热流密度、压力等关键参数对超临界二氧化碳流动不稳定性的单参数影响规律和耦合作用规律，建立界限热负荷的计算关联式，绘制稳定性边界图。本项目成果可为超临界二氧化碳先进发电系统的设计提供理论依据和技术支持。

超临界CO2（SCO2）流动不稳定性的研究是SCO2锅炉和紧凑式换热器热工水力设计的重要基础，也是SCO2布雷顿循环发电系统合理设计和安全运行的重要保障。本项目深入了分析SCO2物性变化规律，创新性地提出了能够准确反映SCO2物性变化特点的物性分区方法，并在此基础上开发出了SCO2流动不稳定性的计算模型。搭建了最大热功率1.2MW、流量5t/h、压力22MPa、温度650℃的实验台，并通过实验获得大量拟临界温度点附近CO2流动不稳定性的实验数据（质量流速300-800kg/m2s，压力8-12MPa，拟过冷数0.6-1.1, 热流密度30-190kW/m2）。通过本项目的实验数据和文献中的实验数据，验证并优化了本项目所开发出的SCO2流动不稳定性计算模型，获得了良好的效果。通过上述模型，获得拟过冷数、热流密度、压力、进出口节流等关键工况参数和管径、管长、壁厚，倾斜角等关键几何参数对SCO2流动不稳定性的影响规律，掌握了界限热负荷、脉动周期等随上述参数的变化趋势。以300MW 28MPa /600°C /620°C 的SCO2锅炉为例，进行了气冷壁内的SCO2流动不稳定性计算研究，并绘制了稳定性边界图。稳定性边界图为SCO2锅炉的热工水力设计提供了参考，可以有效地避免SCO2锅炉在启停过程或者极低负荷运行过程中出现SCO2流动不稳定性现象。本项目获得的计算模型和研究成果被成功应用在了SCO2锅炉气动力设计、SCO2布雷顿循环发电系统的工艺设计中，为系统/锅炉的在启停工况和极低负荷工况的合理设计和可靠运行提供了技术支持。