摇摆对自然循环蒸汽发生器二次侧流动与传热特性的影响

Natural circulation and boiling heat transfer are the important characteristics of the secondary circulation and heat transfer of the natural circulation steam generator, which are the key factors for the safe operation of the steam generator. In this subject, the natural circulation steam generator for marine is taken as the research object. The experimental methods are used to determine the boiling incipience, the boundary of flow pattern transition, the heat transfer characteristics of boiling and the basic problems under swing and natural circulation conditions. The position and change rules of the boiling incipience of natural circulation in the hot side and the cold side of tube-bundle channels under swing conditions are determined and the calculation method of the boiling incipience is given. A visualization method is used to determine the transition point of the flow pattern of the local two phase flow in the tube-bundle channels under the swing condition and establish criterion for flow pattern transformation. On this foundation, the influence rules of swing on natural circulation and boiling heat transfer characteristics are analyzed. A mathematical model of natural circulation flow and boiling heat transfer including swing parameters is established, and the calculation formulas of natural circulation flow rate and boiling heat transfer coefficient are given. Through this research, we can make up for the lack of calculation formula of natural circulation and flow boiling in tube-bundle channels under swing condition, and provide a basis for the design and thermal hydraulic analysis of marine natural circulation steam generator.

自然循环和沸腾传热是自然循环蒸汽发生器二次侧流动和传热的重要特征，是蒸汽发生器运行安全的关键因素。本课题以船用自然循环蒸汽发生器为研究对象，采用实验的方法对摇摆和自然循环条件下沸腾起始点的位置的确定、流型转变边界和沸腾传热特性等基础问题进行研究。确定摇摆条件下管束通道内热侧和冷侧自然循环流动沸腾起始点的位置及其变化规律，给出沸腾起始点的计算方法。采用可视化的方法，确定摇摆条件下管束通道内的局部两相流流型转变点，建立流型转变判定准则。在此基础上，分析摇摆对自然循环流动特性和沸腾传热特性的影响规律，建立包含摇摆参数在内的自然循环流动和沸腾传热的数学模型，给出自然循环流量和沸腾传热系数的计算公式。通过本课题的研究，可弥补摇摆条件下管束通道内自然循环和流动沸腾计算关系式的缺失，为船用自然循环蒸汽发生器的设计和热工水力分析提供基础依据。

由于对海洋环境开发需求的日益增长，海洋核动力设备以及海洋核动力浮动平台备受关注。蒸汽发生器内部流动和传热过程的稳定性直接关系到整个核动力系统的安全性和经济性，海洋条件则会使蒸汽发生器内部流动和传热过程更加复杂。本项目以U型管蒸汽发生器直管段径向非均匀加热管束通道为研究对象，从沸腾起始点（ONB）入手，总结了非均匀加热以及摇摆运动对ONB点的影响规律，考虑非均匀加热因素，基于传统ONB理论模型，推导出适用于非均匀加热条件下ONB的计算公式；探究了竖直、摇摆以及非均匀加热等条件对过冷沸腾和饱和沸腾传热特性的影响，给出了适用于计算时均传热系数的无量纲计算关系式，综合考虑摇摆因素，基于Gungor-Winterton关联式，提出了适用于计算摇摆条件的瞬时传热系数计算关联式；采用可视化观察与高速摄影拍摄的方法，绘制了相关流型图，阐明了流型演变过程；最终，对自然循环条件下流动与传热特性进行了研究，发现了自然循环均匀加热条件下的不对称性，总结了摇摆运动对于自然循环流动与传热的影响规律，探究了非均匀加热与摇摆运动的耦合影响机制。通过本项目的研究，对非均匀加热以及摇摆运动条件下流动传热特性有了更深入的认识，为海洋条件下蒸汽发生器的设计与运行奠定了基础。