脉动热管可视化实验研究进展

脉动热管是一种结构简单、可用于微小空间、高热流密度条件下的传热元件。其优良的传热特性源于内部工质的蒸发、冷凝相变以及两相流动等热-水动力学特性。可视化实验是研究工质流动特性的常用方法，对于理解脉动热管的传热机理非常重要。本文介绍了5种可视化技术手段，简述了近二十年来脉动热管可视化实验观察到的气液相变和多种流型，分析了流型的影响因素，并总结了流动特性和传热性能之间的对应关系。指出目前可视化实验观察到的结果可以定性地解释一些传热现象，却难以定量地揭示脉动热管的传热规律。未来可以将可视化实验中测得的气液塞运动速度、液膜厚度和相分布等信息利用起来，考虑管壁材质的影响，建立更准确的气液两相流模型，用来设计、评估和预测脉动热管的性能。

Research progress on visualization of pulsating heat pipes

Pulsating heat pipe(PHP)is a heat transfer device with simple structure capable of transferring heat effectively in comparatively small space. Visualization experiment is a common method to study flow characteristics of working fluid, which is very important to understand thermo-hydrodynamics of PHP. Previous studies have shown that bubble flow, slug flow, annular flow or semi-annular flow are common flow patterns. Phenomena such as nucleation boiling, coalescence of bubbles, formation of vapor plug and liquid slug were observed in the closed loop PHP. In this paper, five visualization techniques were introduced. Gas-liquid phase transition and flow patterns observed in the visualization experiments of PHPs in recent two decades were briefly introduced. The influencing factors of flow pattern were analyzed, and the correspondence between flow characteristics and heat transfer performance were summarized. At last, future developments were suggested.