横向非均匀加热大宽高比矩形窄缝通道内流动换热特性研究

Narrow rectangular channels in nuclear reactors with plate type fuel elements can enhance heat transfer significantly. However, such channels generally have high aspect ratio, and with non-uniform transverse power as well, which leads to complex lateral migration and mixture of the coolant or bubbles influencing the macroscopic characteristics of flow and heat transfer. Little research on this topic was investigated in the open literatures. Therefore, this proposed project will concentrate on such key problem to perform the flow and heat transfer characteristics of single-phase flow and two-phase flow in the narrow rectangular channel with high aspect ratio under non-uniform transverse power through experimental and theoretical approaches. The uniform/non-uniform heating experiments will be firstly performed to reveal the mechanism and effects of the power distribution on the flow and heat transfer in narrow rectangular channels with high aspect ratio. The visualization experiments will be carried out as well to investigate the bubbles lateral behaviors and the flow pattern conversion. In the theoretical study, the mechanical models of the flow and heat transfer in the narrow rectangular channels with high aspect ratio under non-uniform transverse power will be established based on the advanced numerical computational methods, such as the MPS method, to simulate the microscopic behaviors of bubbles and obtain the macroscopic physical fields. The verification and validation (V&V) will be performed between the experimental study and the theoretical study. This research can provide experimental technology accumulation and basic theoretical supports for the design and safety analysis of advanced nuclear reactors.

核反应堆广泛采用板型燃料元件构成矩形窄缝通道进行强化传热，但此类矩形窄缝通道宽高比大，且存在横向加热不均匀，通道横截面上存在复杂的流体/气泡横向迁移和交混，影响通道内流动换热的宏观特性。目前公开发表的文献未见针对此类通道内流动换热特性研究的报道。因此，本项目着力从实验和理论两方面开展此类矩形窄缝通道内单相、两相流动换热特性研究。实验方面，首先通过均匀/非均匀加热对比实验，揭示功率分布对大宽高比矩形窄缝通道内流动换热的影响规律，获得相应准则关系式；同时开展单面加热可视化实验，从微观上观察大宽高比矩形窄缝内气泡行为、流型发展及其对流动换热的宏观影响。理论方面，基于先进数值计算方法（如MPS方法），建立横向非均匀加热大宽高比矩形窄缝通道内流动换热的机理模型，模拟横截面上气泡的微观行为，同时获得宏观物理场，与实验相互验证和校核。本项目可为先进核反应堆的设计和安全分析提供实验技术积累和基础理论支持。

板型燃料元件具有比功率高、结构紧凑、燃耗高、安全性好的特点，可作为核潜艇等国防装备的动力来源，但其中热工安全特性的研究是发展先进核动力系统亟待解决的基础和关键科学问题。相邻燃料板之间矩形流道存在宽高比大且横向加热不均匀的特点，造成冷却剂沿横向上不可忽略的迁移和交混，影响通道内流动换热的宏观特性。本课题采用实验研究与理论分析相结合的方法，深入研究了横向均匀/非均匀加热功率分布模式下矩形窄缝通道内单相和两相流动换热特性。设计了横向加热功率可调的矩形窄缝通道实验段，搭建了矩形通道流动换热闭式实验回路，在此基础上开展了横向均匀/非均匀加热条件下矩形窄缝通道内流动和换热特性实验研究，对比分析了横向功率分布模式对单相流动阻力和换热特性的影响，以及系统压力、质量流速、含气率和横向功率分布模式等参数对两相流动压降、沸腾起始点和饱和沸腾换热特性的影响，对现有关系式进行了适用性评价，并利用本文实验数据和文献数据，充分考虑窄小通道结构特征和横向功率分布形式的影响，建立了单相和两相换热系数、两相流动压降以及ONB点壁面过热度实验关联式。此外，基于先进数值方法，将单个矩形通道视作并联多通道并沿轴向和横向划分控制体，利用Fortran语言编制了热工水力计算分析程序，获得了流场和温度场的局部参数分布，揭示了横向功率分布方式对矩形通道内流动换热特性的影响机理。本项目丰富和完善了矩形窄缝通道流动和传热特性实验数据库，为板型燃料元件在新型战略核潜艇等国防装备的应用方面提供了珍贵的热工水力基础实验数据和必要的热工水力特性分析。针对新型核动力装置所提出的空间和重量限制以及提高综合性能的要求，本项目研究成果具有提高热工水力设计精度的重要科学意义和工程价值。