高温条件下换热单元流动/传热/应力耦合及强化传热机理研究

High-temperature heat transfer refers to a process with working temperature above 650 ℃ for the media, such as gas-gas fluids. It is founded that high temperature difference，high operating pressure and high thermal stress are the typical characteristics, which are quite different compared to the ones in the low-temperature heat exchange process. High-temperature heat exchange technology is the key factor to improve the efficiency of the systems,such as the externally fired combined cycle (EFCC) and the hydrogen production sulfur-iodine (S-I) thermochemical cycle. There have been some researchs in EU, U.S. and China, which mainly focused on the engineering applications of high temperature heat exchange technology, with little attention on fundamental but significant issues, such as the internal transport phenomenon and thermal stress, especially the coupling mechanism among velocity field，temperature distribution and thermal stress. The present project is to investigate the fluid flow，heat transfer，thermal stress,with focus on their coupling characteristics in heat transfer units under high operating temperature by employing experimental, numerical simulation and theoretical analysis methods. The main goal is to identify the thermal boundary features for gas-gas fluid flow at high operating temperature conditions; to develop the numerical analysis approaches which consider the coupling effects of multiphysics transport phenomena; to analyse the interaction effects of flow, heat transfer, stress and creep on the heat exchanger performance and structural reliability; and to establish the enhanced heat transfer principle and to develop enhanced heat transfer evaluation method and the optimization design method under material safety conditions. It is expected that the research methods and findings developed in this project have significant scientific impacts and practical applications,to broaden and deepen the understanding of complex transfer process in the advanced energy systems under high operating temperatures, as well as supply the theoretical support for relevant engineering and industries.

高温换热指介质温度在650℃以上条件下的换热，一般发生在气-气双流体环境下，并伴随着大温差、高压和高应力等特征，与常温及低温换热工作条件有着本质区别，是制约外部燃烧联合循环和碘-硫热化学制氢循环等提高效率的关键因素。当前欧美和国内学者对高温换热技术开展了初步应用研究，但对其内部的流动传热和应力特性缺乏深入的认识，尤其是流场温度场与应力场之间的相互耦合作用。本项目拟采用实验测量、数值模拟和理论分析方法，研究高温条件下换热单元内流动传热和应力耦合特性，旨在明确气-气双流体流动下高温换热单元内的热边界特性，建立高温条件下多物理场耦合数值分析模型，阐明流动传热、应力和蠕变等因素对换热效能和结构可靠性的影响机制，提出满足结构安全性条件下强化传热原则、强化传热评价方法和综合性能优化设计方法。本项目可以拓宽和深化对高温条件下能量传递现象的认识，并为有关应用提供理论支持，具有重要的学术意义和工程实用价值。

高温换热器是在650℃以上高温条件下实现冷热流体热量交换的设备，两侧换热介质通常均为气体。近年来，伴随着能源的日益紧张和环境破坏，新能源开发、余热回收利用和高温热污染控制越来越受到重视，迫切需要更为高效的动力系统，而高效的动力系统往往需要更高的操作温度，因此高温换热器在外燃式燃气轮机循环系统、超高温气冷堆系统和碘-硫热化学高温制氢循环系统等高效动力系统中得到了广泛的应用，作为影响整个循环系统效率的关键设备，高温换热器已成为制约这些循环系统能否得以实际应用的关键因素之一。本项目采用实验测量、数值模拟和理论分析方法，分析了气-气双流体流动下的高温换热单元内的热边界特性， 研究了高温条件下流场、温度场和力场等多物理场耦合模型的建模技术，尤其是流动和热边界层动网格实现方法，总结得到可以完成双向影响和耦合分析的高温换热单元内多物理场耦合数值分析模型，深入分析了流场、温度场和力场的相互作用机理。开展了高温条件下换热单元流动和传热的实验，确定了高温气-气流动条件下的表面对流换热系数分离方法，获得相应的流动传热和应力规律，为理论分析和数值研究提供实验验证。通过对内翅片管换热芯体流-热-力多物理场综合性能分析和优化，提出了插管式内翅片管的内管和内翅片不焊接以及保持0.5mm最优间距的设计方案，该新型结构在高温条件下具有换热性能好、热应力低的优点，且阻力损失在容许范围内，达到了强化换热与可靠性的较优组合。本项目研究结果可以拓宽和深化对高温条件下能量传递现象的认识，并为有关应用提供理论支持，具有重要的学术意义和工程实用价值。