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

以水、乙醇和R141b为工质，研究了由加热段1块铜板、绝热段和冷却段24根铜管组成的脉动热管（PHP）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，添加水的PHP在较大热负荷范围内具有较高的性能。为了增强含有R141b的PHP的性能，在液体中加入了小的金刚石颗粒。在整个热负荷范围内，R141b颗粒的流动搅拌强化了热传导，从而提高了PHP的性能。除管式旋流器外，还研究了弯曲槽道板式旋流器。提出了一种新型的通道构型，即连接通道两端的通道也弯曲。结果表明，在以乙醇为工质时，新型通道的传热性能优于传统通道。此外，在一个简单的PHP上进行了基本的实验，即单个液体段塞在直线通道中的振荡。通道两端区域被加热，中心区域被冷却。通过高速视频显示了液体段塞的振荡过程，并测量了蒸汽区的压力变化。阐明了液体振荡与压力振荡之间的相位滞后对液体产生功，这是PHPs的主要机理。对振荡液体引起的显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估计了潜热输运的作用。

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.