定位格架影响条件下堆芯通道超临界流体流动与传热机理研究

Up to now, the grid spacer has been wildly used to enhance the forced convection heat transfer of fluid within reactor core. However the knowledge and utilization of this traditional heat transfer augmentation technique is confined to the single phase water and/or water-vapor two-phase mixture under sub-critical pressure. The application of this technology to the supercritical water largely depends on the adequate understanding of the heat and mass transfer mechanisms of supercritical water under the influence of grid spacer within supercritical water-cooled reactor core, which is meager to us due to the lack of correlative fundamental research. In this project, the basic physical features, as well as the key scientific issues involved in this very field will be studied, including the grid spacer effect on the dissimilation of flow form and heat transfer of supercritical fluid, the formation and changing rule of secondary flow field inside and downstream of the grid spacer, the mechanism of action of swirling flow, along with the drastic change of thermal physical properties, the buoyancy and thermal acceleration, on the heat and mass transfer, the impact of upstream flow on the head of grid spacer and the sudden expansion of downstream flow behind the end of grid spacer, etc. By combining the experimental examination, numerical simulation and theoretical analysis, the heat and mass transfer mechanisms of supercritical fluid under the influence of grid spacer within reactor core will be accurately revealed. The effect laws of sub-channel structure, thermal physical property and the thermodynamic parameter on the heat and mass transfer characteristics , as well as the empirical formula to predict the enhanced heat transfer by grid spacer, will be acquired. It is expected to provide part of theory foundation for the development of heat transfer augmentation technique of supercritical fluid.

采用定位格架增强堆芯工质强制对流传热能力是目前反应堆中的传统强化传热技术。迄今为止人们对该技术的认识和利用仅限于亚临界压力下的单相水或汽水两相混合物，而对定位格架影响条件下的堆芯内超临界工质的流动和传热机理认识不够，基础研究不足。本项目拟对定位格架作用下堆芯通道内超临界流体流动形态异化和传热效果变化、定位格架内部及下游二次流场形成及变化规律、漩涡流对流动与传热的作用机制、超临界工质剧烈物性变化、浮升力及热加速度对流动传热的影响、上游流动对定位格架端部冲击和格架尾流突然膨胀现象等相关基本物理过程和关键科学问题进行研究，采用实验测试、数值计算与理论分析相结合的手段，准确揭示定位格架对堆芯通道内超临界流体流动与传热影响机理，获得通道形状、流体热物性及热工参数对超临界工质流动与传热的影响规律，提出经验关联式,为超临界传热强化技术的发展提供一定的理论基础。

采用定位格架增强堆芯工质强制对流传热能力是目前反应堆中的传统强化传热技术。迄今为止人们对该技术的认识和利用仅限于亚临界压力下的单相水或汽水两相混合物，而对定位格架影响条件下的堆芯内超临界工质的流动和传热机理认识不够，基础研究不足。本项目拟对定位格架作用下堆芯通道内超临界流体流动形态异化和传热效果变化、定位格架内部及下游二次流场形成及变化规律、漩涡流对流动与传热的作用机制、超临界工质剧烈物性变化、浮升力及热加速度对流动传热的影响、上游流动对定位格架端部冲击和格架尾流突然膨胀现象等相关基本物理过程和关键科学问题进行研究，采用实验测试、数值计算与理论分析相结合的手段，准确揭示定位格架对堆芯通道内超临界流体流动与传热影响机理，获得通道形状、流体热物性及热工参数对超临界工质流动与传热的影响规律，提出经验关联式,为超临界传热强化技术的发展提供一定的理论基础。.本项目首先利用SSG雷诺应力模型对超临界反应堆六边形内部子通道中超临界水的流动与传热进行了数值模拟，从方法上实现了对复杂非圆通道内超临界流体强制/混合对流过程的准确捕捉。数值模拟所得阻力、壁温以及传热系数等参数与实验结果的吻合较好。结果表明，SSG雷诺应力模型可以有效表征超临界流体在非圆通道中流动与传热的细微特征，可用于研究定位格架下游超临界流体流动与传热的数值模拟。.其次，进一步细化了数值模拟结果，得到了压力，质量流速以及壁面热负荷等系统参数对超临界流体流动和传热的影响规律，获得了超临界反应堆设计工况下超临界水在内部子通道中的阻力及流动传热关联式，并将关联式与现有传热公式进行了对比。.同时，搭建了超临界反应堆四边形及三角形子通道内超临界流体流动与传热实验台。实验测量了管壁温度，进出口压差以及定位格架下游传热系数，定位格架局部阻力等参数。实验结果表明，子通道内超临界流体的流动与传热存在较强的周向不均匀性，窄缝区换热较弱而中心区换热能力较强。压力，热流密度及质量流速等系统参数对流动与传热影响较大，子通道传热周向的不均匀性也会受到一定影响。.在前期数值模拟及实验研究的基础上，进一步展开了超临界反应堆子通道内超临界流体熵产行为的数值研究，采用热力学第二定律分析子通道内超临界水在流动与传热过程中的能量耗散及转换现象，系统研究了超临界水传热强化现象与近壁面边界层结构及状态参数的关系，并基于已有计算结果进一步对定位格架结构的优化方向进