小温差多热源热虹吸回路的耦合特性及稳定性研究

This project investigates the coupling and stability characteristics of loop thermosyphon with small temperature difference and multi-heat source, which often varies with space and time. A visual heat transfer experiment platform will be set up and investigations will be conducted experimentally and theoretically. For the startup under multi-heat source with varied space and time distributions, response of each evaporator and the coupling characteristics will be investigated and the conditions when unstable phenomenon and corresponding startup failure occur will be analyzed. Working conditions and structures which are suitable for the stable startup will be proposed; For the operation under multi-heat source with varied space distributions, the flow and heat transfer distributions of each branch and the coupling characteristics will be investigated and the amplitude and frequency of oscillation will be analyzed. The circulation failure under some unfavorable space distributions will be summarized. For the operation under multi-heat source with varied time distributions, response of each evaporator and the coupling characteristics will be investigated and the flow regime transition and corresponding instability due to the heat source varied with time will be concerned. Critical working conditions of stability and structures which are suitable for the stable operation will be proposed. Through the investigation on the above basic problems of thermodynamics and heat transfer, the development and application of multi-heat source heat transfer technology will be promoted. Also, the study and knowledge of loop thermosyphon with multi-heat source and small temperature difference and other natural circulations will be explored deeper.

本项目针对小温差多热源热虹吸回路在多热源变空间与时间分布条件下，各蒸发器支路间的耦合特性和回路稳定性问题，搭建可视化多蒸发器热虹吸实验台进行实验和理论研究。研究在多热源变空间与时间分布条件下的启动中, 各蒸发器的启动响应与其中的耦合作用机理,分析不稳定现象及相应启动失败现象的发生条件,提出有利于平稳可靠启动的工况范围和结构；研究在多热源变空间分布运行中,各支路的流动与传热的分布特性及各支路的耦合影响,分析工质参数振荡的幅度和频率，总结在某些不利空间分布条件下的循环流动失败现象；研究在多热源变时间分布运行中,各蒸发器的动态响应和其中的耦合作用，关注热源随时间变化带来的流型转变以及产生的不稳定现象,提出稳定运行临界条件和循环稳定性更高的回路结构形式。通过上述热力学和传热学基础问题研究，促进多热源传热技术的发展和应用，深入对小温差多热源热虹吸回路等自然循环现象的研究和认识。

小温差多热源热虹吸回路在数据中心与大科学装置节能冷却领域具有良好的应用前景。在回路稳定性方面，发现了启动过程中由于蒸发器之间状态差异造成的温度突变现象，总结指出其发生机理为蒸发器间温度差异造成的工质流动方向突变；发现了各蒸发器的温度峰谷相对振荡现象，采用可视化实验分析，指出其发生机理为蒸发器相互竞争引起的周期性改变方向的旁通流；除以上两种特有现象外，总结了通常情况下的温度波动现象发生工况以及幅值与频率，获得了利于循环稳定的工况范围和结构形式；在回路耦合特性方面，研究了不同加热量分配下，各蒸发器的启动时间与温度超调现象，分析了其与蒸发器间耦合影响的关系；针对现有多热源热虹吸回路耦合影响研究主要是定性研究的问题，创新性地引入耦合影响因子，为量化评估不同结构下蒸发器间的耦合影响大小提供了有效方法；进一步地，通过变工况下的可视化实验，获得了在不同充液率和加热量分配下多蒸发器之间量化和可视化的耦合影响特性。本项目的研究成果有助于小温差多热源热虹吸回路在数据中心和大科学装置冷却等领域的推广应用。