Effect of charging ratio within ideal range on temperature oscillation for a loop heat pipe

doi:10.16085/j.issn.1000-6613.2018-0586

Abstract

Abstract: A flat loop heat pipe (FLHP), the evaporator with transparent cover, was designed and manufactured to investigate the effect of charging ratio on temperature oscillation. The visual study of the two-phase flow in the evaporating zone, wick and compensation chamber was given. Three charging ratios were tested to investigate the characteristics of start-up and operation of the LHP. It was found that Type Ⅰ cyclical temperature oscillation occurred at low heat loads with low charging ratios. However, as the charging ratio was raised, Type Ⅱ cyclical oscillation was observed under the same heat loads. The distinction of two types of temperature oscillation was whether the dry out happened in compensation chamber. Correspondingly, intermittent backflow from the condenser to the compensation chamber was visually observed. It could be concluded that temperature oscillations at low heat loads was resulted from poor dynamic distributions of working fluid in the whole LHP. As the heat load raised, the dynamic distributions of working fluid became stable, so the temperature oscillation disappeared. It was shown that the charging ratio of 52% had the best performance and there was the least amplitude and the lowest heat load when temperature oscillation disappeared.

Key words: heat transfer, phase change, evaporation, temperature oscillation, charging ratio

摘要： 为研究充液率对平板式环路热管（flat loop heat pipe，FLHP）温度振荡的影响，设计并制造了一类带有透明蒸发器外壳的平板式环路热管，以实现蒸发区域、吸液芯和储液槽内蒸汽与液体流动的可视化研究。实验通过改变充液率对环路热管的启动和运行特性进行分析，发现在低热负荷条件下，当充液率较低时的环路热管运行温度出现第一类周期性振荡，而充液率增高后的环路热管运行温度则出现第二类周期性振荡，两种振荡的区别在于储液腔内是否存在干涸现象。而对应的可视化研究揭示该类环路热管低负荷时储液槽内液体回流出现了不连续现象，这意味着管内工质动态分布不均并最终导致了温度振荡。同时随着热负荷的提高，环路热管内部工质动态分布亦趋于稳定，温度振荡得以改善。研究表明：针对该类环路热管，52%的充液率综合性能最优，其温度振幅较小，且能在更低热负荷下进入稳定状态并同时具有较低的壁面工作温度。

关键词: 传热, 相变, 蒸发, 温度振荡, 充液率

CLC Number:

TK124

HU Zhuohuan, ZHOU Yuren, XU Jiayin. Effect of charging ratio within ideal range on temperature oscillation for a loop heat pipe[J]. Chemical Industry and Engineering Progress, 2018, 37(12): 4551-4557.

胡卓焕, 周宇仁, 许佳寅. 理想范围内充液率对环路热管温度振荡的影响[J]. 化工进展, 2018, 37(12): 4551-4557.

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