高温/高压条件下复杂微细通道内对流传热强化及局部纵向导热效应研究

High temperature/high pressure heat transfer technology is one of the most important technologies in the high-efficiency energy and power systems, such as the very high-temperature gas-cooled reactor and the supercritical carbon dioxide Brayton cycle. However, the application and efficiency improvement of these systems are restricted by the efficiency of heat transfer under ultra conditions. For the popose of enhancing the heat transfer performance, the heat transfer channels at high temperature/high pressure are developing towards to directions of smaller and more complex structures. However, the scholars at home and abroad haven't carried out deeper research on the mechanism of heat transfer caused by the significant variations of physical properties along the main flow direction at high temperature and high pressure, including the effect of local longitudinal heat conduction, the relationship of heat transfer and pressure drop performances between the local and whole channels, and the enhanced heat transfer method in the mini-channels under the ultra conditions. The present study will investigate the convective heat transfer mechanism coupled with longitudinal heat conduction in the complex mini-channels under the ultra conditions (high temperature condition≥900℃; supercritical pressure). The goals are to analyze the effect of large-scale and small-scale longitudinal heat conductions, to recognize the mechanism of local heat transfer along the main flow direction, to achieve the analytical solution of longitudial heat conduction and the heat transfer expressions of the whole channel derivated from the cell, and to propose the enhanced heat transfer method for the ultra conditions. The results will give a theoretical support for the high-efficiency heat transfer technology under ultra conditions and a supplement of heat transfer method for the room condition, which has important academic values and engineering applications.

高温/高压换热技术是超高温气冷堆、超临界二氧化碳布雷顿循环等高效能源动力系统的关键技术之一，发展高效的高温/高压传热技术是推广这些系统走向实际应用和提升效率的关键所在。为了强化传热，当前高温/高压传热通道朝着微细尺寸和复杂结构发展，但是国内外学者尚未对复杂微细通道在高温和高压条件下由于沿程强变物性特征所产生的传热规律开展深入研究,主要包括局部纵向导热效应、沿程与整体能量传递特性的相互关系和传热强化方法。本项目旨在对极端条件下（高温≥900℃；超临界压力）复杂微细通道内对流传热机理进行研究，揭示整个复杂微细通道的小尺度和大尺度纵向导热效应，以及沿程能量传递机理，获得纵向导热的分析解和局部单元能量传递特性外推整体能量传递特性的计算方法，提出适用于极端条件的强化传热方法。研究结果可为极端条件下的高效强化传热技术提供理论支持，也是常温条件下强化传热技术的有益补充，具有重要的学术意义和工程应用价值。

本项目以微型燃气轮机、超高温气冷堆、超临界二氧化碳布雷顿循环等高效能源动力系统中所急需的高温高压换热设备为研究对象，从极端高温高压条件下复杂微细通道的纵向导热机理、局部能量传递特性及计算方法、高效低阻的强化传热方法、制备工艺以及传热性能实验测试等方面开展了较为全面的研究。提出了基于双流体传热通道分离式流动传热模型的各向异性纵向导热数值方法以及纵向导热计算公式。发现小尺度纵向导热效应是由波纹板中温度的不均匀分布造成的，小尺度纵向导热可以促进波纹板温度均匀分布以及提高传热性能。发现在高温传热通道内的流动传热不能达到充分发展阶段，但是其无量纲速度场和温度场与常物性没有本质区别。对于高温双流体通道的整场数值计算，发现在较高雷诺数下可采用恒壁温边界的周期单元来简化计算，在较低雷诺数下可采用线性壁温边界的周期单元来简化计算。发现两侧流量的变化对热阻分布情况有重要影响，提出了拟临界点附近基于热阻分布的局部强化传热方法。探讨了复杂微细高温高压通道的化学蚀刻工艺，获得了具有良好形貌的直通道、Z字形通道、翼型通道等复杂通道的印刷电路板换热器换热板，揭示了初始宽度、蚀刻溶液成分、浓度等参数对蚀刻速度、形貌、侧蚀和粗糙度的影响机制。自主设计和搭建了超临界CO2高压传热实验台，获得了套管和印刷电路板换热通道的传热实验关联式。相关研究结果对于深入了解高温高压传热机理以及开发高效的高温高压换热设备具有重要指导意义。