Abstract The effects of oscillation amplitudes on heat transfer mechanisms of pulsating heat pipes (PHPs) are experimentally investigated. For this, a five-turn closed-loop micro PHP (MPHP) with overall dimensions of 28 × 67.5 × 1.6 m m 3 is made of glass top and silicon bottom. A meandering micro-channel with hydraulic diameter of 0.835 mm is engraved on the glass. Ethanol is selected as the working fluid and the filling ratio is fixed at 45%. Experiments are performed at various input powers in a vertical orientation with bottom-heating mode. The oscillation amplitude, as a representative parameter of the flow characteristics, is obtained from a high-speed imaging technique. The heat flux distribution at the interface between the fluid and the wall is simultaneously obtained from a high-speed infrared imaging technique. From the synchronization of the images of the flow visualization and heat flux distribution, the transfer of heat occurring at the interface between the fluid and the wall is divided between sensible heat and latent heat. Then, the heat transfer mechanisms of the MPHP are investigated by quantitatively analyzing the proportion of latent heat to overall heat. As the input power increases from 7 W to 16 W, the oscillation amplitude increases from 3.4 mm to 8.3 mm. The proportion of latent heat continues to increase from 54.8% to 81.9%. Due to the increased proportion of latent heat, the thermal resistance of the MPHP decreases by 13.5%. From these experimental results, it is confirmed that the proportion of latent heat increases with the oscillation amplitude, resulting in a decrease of the thermal resistance of the MPHP. These experimental findings can give a clue to improving the thermal performance of PHPs: the thermal performance of PHPs can be increased by increasing the oscillation amplitude or the proportion of latent heat in either the evaporator section or the condenser section.

中文翻译：

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振幅对脉动热管传热机理的影响

摘要 通过实验研究了振幅对脉动热管（PHPs）传热机制的影响。为此，一个整体尺寸为 28 × 67.5 × 1.6 mm 3 的五圈闭环微型 PHP (MPHP) 由玻璃顶部和硅底部制成。玻璃上刻有水力直径为 0.835 毫米的蜿蜒微通道。工作液选用乙醇，填充率固定为45%。实验是在垂直方向的各种输入功率下进行的，底部加热模式。振荡幅度作为流动特性的代表参数，是通过高速成像技术获得的。流体与壁面界面处的热通量分布是通过高速红外成像技术同时获得的。从流动可视化和热通量分布图像的同步来看，发生在流体和壁之间界面处的热量传递分为显热和潜热。然后，通过定量分析潜热占总热量的比例来研究 MPHP 的传热机制。随着输入功率从 7 W 增加到 16 W，振荡幅度从 3.4 mm 增加到 8.3 mm。潜热占比从54.8%继续提高到81.9%。由于潜热比例的增加，MPHP的热阻降低了13.5%。从这些实验结果可以证实，潜热的比例随着振荡幅度的增加而增加，导致MPHP的热阻降低。