Study on improvement of pulsating heat pipe and prediction of heat transport characteristics

以水、乙醇和R141b为工质，研究了由一块铜板和24根铜管组成的脉动热管的传热特性。结果表明，添加R141b的PHP在较低热负荷范围内具有较高的性能，而使用水的PHP在较大的热负荷范围内具有较高的性能。为了提高R141b的性能，在液体中加入了较小的金刚石颗粒。在整个热负荷范围内，由于颗粒引起的流动搅拌强化了换热，R141b在整个热负荷范围内的性能优于R141b。除管式PHP外，还研究了一种带有弯曲槽道的板式PHP。提出了一种新型的航道布置形式，即连接航道两端的航道也是曲折的。结果表明，在以乙醇为工质的情况下，新型通道具有比常规通道更高的换热性能。在此基础上，对一个简单的液塞进行了基本实验，即单个液塞在直流道中的振荡。通道的两端区域被加热，中心区域被冷却。通过高速摄像显示了液塞的振荡过程，并测量了蒸汽区压力的变化。阐明了液体振荡和压力振荡之间的相位滞后引起液体做功，这是PHPS产生的主要机理。对振荡液体的感热输运进行了精确的数值分析，并通过实验结果与数值结果的比较，评价了潜热输运的作用。

Heat transport characteristics of a pulsating heat pipe (PHP), which consists of a copper plate in the heating section and 24 copper tubes in the adiabatic and cooling sections, has been investigated using water, ethanol and R141b as the working fluid. It was found that PHP with R141b has higher performance in lower heat load range, and that with water has higher performance in larger heat load range. In order to enhance the performance of PHP with R141b, small diamond particles were added to the liquid. The PHP performance using R141b with particles was superior in the whole range of heat load due to the heat transfer enhancement by the flow agitation owing to the particles. In addition to the tubular PHP, a plate-type PHP with a meandering groove channel was investigated. A new type channel configuration was proposed, that is, the channel which connects both ends of channels was also meandered. It was revealed that the new type channel has higher heat transport performance than the conventional one when ethanol was used as the working fluid. Further, a fundamental experiment was performed on a simple PHP, that is, an oscillation of a single liquid slug in a straight channel. Both end regions of the channel were heated, and the center region was cooled. The oscillation of liquid slug was visualized by a high-speed video, and the change of pressure in the vapor region was also measured. It was clarified that the phase lag between the liquid oscillation and pressure oscillation causes a work to the liquid, which is the principal mechanism of PHPs. An exact numerical analysis was performed for the sensible heat transport due to the oscillating liquid, and the role of latent heat transport was estimated by the comparison between experimental and numerical results.