Optimization in the geometry structure of the pulsating heat pipe (PHP) may provide an effective method to improve the heat dissipation capacity. In this study, tandem tapered nozzles are proposed to promote the unidirectional flow in a three-dimensional (3D) closed-loop PHP (CLPHP). For comparison, two six-turns CLPHPs comprised of 12 glass tubes with a 2 mm inner diameter (ID) and 13 silicone hoses with a 2.5 mm ID were examined to study the effect of tapered nozzles. Specifically, one (ordinary) had an equal glass tube ID, while the other one (asymmetrical) adopted glass tubes that had one tapered nozzle end formed by burning and melting the end from 2 mm into 0.95 mm ID. A series of experiments were performed to investigate the effects of filling ratios (ethanol) and heating powers on the thermal resistance, start-up time, and flow patterns. Results showed that the thermal resistance was reduced by 29.5% after the optimization, and the unidirectional flow was significantly promoted. Moreover, the dry-out phenomenon that happened in the ordinary CLPHP at the 40% filling ratio was also prevented in the asymmetrical one. Finally, we explain the variation trend of start-up time from the driving force theory. The present application of the tandem tapered nozzles in the 3D CLPHP provides an effective, reliable, and easy-to-implement method for improving the heat transfer performance, which leads to the direction for the future design of the PHP. © 2020 Elsevier Inc.

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串联锥形喷嘴三维脉动热管的实验研究

脉动热管（PHP）几何结构的优化可以提供一种有效的方法来提高散热能力。在这项研究中，提出串联锥形喷嘴以促进三维 (3D) 闭环 PHP (CLPHP) 中的单向流动。为了进行比较，检查了由 12 根内径 (ID) 为 2 毫米的玻璃管和 13 根内径为 2.5 毫米的硅胶软管组成的两个六圈 CLPHP，以研究锥形喷嘴的效果。具体来说，一个（普通）具有相等的玻璃管内径，而另一个（不对称）采用具有一个锥形喷嘴端的玻璃管，该喷嘴端是通过将端部从 2 毫米燃烧熔化成 0.95 毫米 ID 形成的。进行了一系列实验以研究填充率（乙醇）和加热功率对热阻、启动时间和流动模式的影响。结果表明，优化后热阻降低29.5%，单向流动得到显着促进。此外，在不对称的情况下，也防止了普通 CLPHP 在 40% 填充率下发生的干燥现象。最后，我们从驱动力理论解释了启动时间的变化趋势。目前串联锥形喷嘴在3D CLPHP中的应用为提高传热性能提供了一种有效、可靠且易于实施的方法，为PHP的未来设计指明了方向。© 2020 爱思唯尔公司 在不对称的情况下也防止了在40％填充率下普通CLPHP中发生的干燥现象。最后，我们从驱动力理论解释了启动时间的变化趋势。目前串联锥形喷嘴在3D CLPHP中的应用为提高传热性能提供了一种有效、可靠且易于实施的方法，为PHP的未来设计指明了方向。© 2020 爱思唯尔公司 在不对称的情况下也防止了在40％填充率下普通CLPHP中发生的干燥现象。最后，我们从驱动力理论解释了启动时间的变化趋势。目前串联锥形喷嘴在3D CLPHP中的应用为提高传热性能提供了一种有效、可靠且易于实施的方法，为PHP的未来设计指明了方向。© 2020 爱思唯尔公司