超临界机组深度调峰工质流动不稳定试验与理论计算

Experiment and theoretical calculation of flow instability in deep peak-shaving of supercritical units

为研究超临界机组深度调峰低负荷状态管内流动不稳定性,对20°倾角的倾斜光管内流动不稳定性进行研究,总结了典型沸腾起始点脉动、压力降型脉动和密度波型脉动的脉动特性,重点分析了低压力参数下质量流速、入口过冷度和上游可压缩容积等参数对沸腾起始点脉动和密度波型脉动的影响规律。结果表明,质量流速的增大能削弱管内流动脉动,提高受热管内工质的流动稳定性;入口过冷度和可压缩容积对脉动的影响具有双重作用,规律较复杂。此外,建立了典型的一维单通道垂直上升管不稳定性计算回路,并计算其热流密度和质量流量变化。根据计算结果,垂直上升管进、出口流量随时间呈反相脉动,同时得到回路不稳定性的临界热流密度和临界质量流速。在机组低负荷运行工况下,受热管的热流密度远低于临界热流密度,质量流速远高于临界质量流速,才可保证受热管内工质流动的稳定性。倾斜管和垂直上升受热管管内工质的流动不稳定均可通过无量纲参数计算进行判定。

In order to study the flow instability in the tube during the deep peak shaving and low load state of supercritical units,the flow instability in the inclined smooth tube with 20°inclination angle was experimentally studied and analyzed.The typical oscillation characteristics of nucleate boiling starting point oscillation,pressure drop oscillation and density wave oscillation were summarized,and the effects of mass flow rate,inlet subcooling and upstream compressible volume on nucleate boiling strarting point oscillation and density wave oscillation under low pressure parameters were emphatically analyzed.The results show that the flow pulsation in the tube can be weaken and the flow stability of the working fluid in the heating tube can be improved due to the increase of mass flow rate.The influence of inlet subcooling and compressible volume on the oscillation is dual and the law is relatively complex.In addition,a typical one-dimensional single channel vertical tube instability calculation loop was established,and the variation of heat flux and mass flow were calculated and analyzed.According to the results,the inlet and outlet flows oscillate inversely with time,and the critical heat flux and critical mass flow rate of loop instability are obtained.In the low load operation condition of the unit,the heat flux of the heating tube is much lower than the critical heat flux,and the mass flow rate is much higher than the critical mass flow rate,so as to ensure the stability of the working fluid flow in the heating tube.The flow instability of the working fluid in the inclined tube and the vertical upward heating tube can be determined by dimensionless parameters.