Abstract:

Heat transfer enhancement and effects of graphene oxide (GO) nanofluid on a pulsating heat pipe (PHP) were studied experimentally. Results showed that heat transfer performance of the GO/water PHP was significantly affected by the filling ratio, concentration and heating power. At a lower filling ratio, e.g. 30%, the PHP worked under the combination of two-phase thermosyphon and pulsation role, showing the advantage of lower thermal resistance but the shortage of easier dry-out. Adding GO nanoparticles could improve the heat transfer performance, such as reducing the thermal resistance and alleviating dry-out effectively. Especially in the mass fraction of 0.05%—0.08% and Q=10—50W, the thermal resistance of the GO/water PHP was lower about 38.1%—74.1% than that of the water PHP. In the mass fraction of 0.08%—0.1%, the dry-out limitation Q_max was higher about 33% than that of pure water. At a higher filling ratio, e.g. 80%, the PHP had smaller vapor phase space for the fluid to move or pulsate. Thus, its overall operation was not quite satisfactory compared with the lower and medium filling ratios. At a higher filling ratio (FR=80%), adding GO nanoparticles could not improve the heat transfer performance of the PHP apparently, and the heat transfer performance was even deteriorated at higher concentrations (the mass fraction of 0.1%). In terms of the thermal resistance and dry-out limitation, the PHP achieved the best overall performance at a medium liquid filling ratio (FR=50%), and especially in the mass fraction of 0.03%—0.08% and Q=20—105 W, thermal resistance reduced about 18.9%—54.4% compared with the water PHP, showing the obvious enhancement effect. Finally, an empirical correlation was fitted based on Kutateladze number (Ku), Bond number (Bo), Morton number (Mo), Prandtl number of liquid (Pr), and Jacob number, to predict the thermal performance of the GO/water PHP with the nanofluid mass fraction in the range of 0—0.1% and the filling ratio in the range of 30%—80%.

Key words: pulsating heat pipe, graphene oxide, heat transfer enhancement, filling ratio, concentration, experimental correlation

摘要：

实验研究了氧化石墨烯（GO）纳米流体对脉动热管（PHP）传热性能的影响。结果表明：充液率、浓度及加热功率显著影响脉动热管的传热性能。在小充液率（FR=30%）时，PHP更多是在重力辅助热虹吸管以及脉动热管的共同作用下工作，热阻较低，但容易烧干；添加GO纳米颗粒可改善流体传热性能，降低PHP热阻，延缓烧干；尤其在质量分数0.05%~0.08%、加热功率10~50W时热阻可比纯水降低38.1%~74.1%；在质量分数0.08%~0.1%时，烧干极限Q_max可比纯水提高33%。在大充液率（FR=80%）时，气相空间受限，流体运动阻力较大，PHP整体运行性能较差。添加GO纳米不能明显改善PHP传热性能，在高浓度（质量分数0.1%）时还会恶化传热性能。综合考虑热阻及烧干极限，PHP在中等充液率（FR=50%）时整体运行性能最佳；且存在一个合适的工作范围（质量分数0.03%~0.08%，加热功率20~105W），使PHP热阻比纯水下降18.9%~54.4%之间，强化作用明显。最后，在实验基础上，综合应用Ku、Pr、Ja、Bo、Mo等量纲为1数组合，拟合得到实验关联式预测GO/水PHP传热性能，适用于30%~80%充液率下，质量分数0~0.1%的GO/水纳米流体脉动热管。

关键词: 脉动热管, 氧化石墨烯, 传热强化, 充液率, 浓度, 关联式