Abstract:

Loop heat pipe(LHP) is a kind of flexible and efficient two-phase flow heat transfer device, which can achieve high heat transfer efficiency through phase change of working fluid and adsorption capability of porous wick. The multi-evaporator loop heat pipe(MeLHP) is based on such structure of LHP with parallel connection of multiple evaporators to achieve efficient heat collection and dissipation of multiple heat sources, which is suitable for the cooling of multi-array infrared detectors in space exploration technology. The test prototype adopted the structure of a multi-evaporator loop heat pipe with three evaporators. The pipelines were connected in parallel by gas coupling and arranged asymmetrically. The working temperature was set to be 170K while ethane was used as working fluid. Taking the experimental data of single evaporator loop heat pipe as reference, the experimental study of MeLHP’s operating characteristics was conducted under different heating power and heating methods. Then the effect of liquid charging ratio on MeLHP‘s performance was experimentally studied based on working characteristics of compensation chambers. Experiments showed that the MeLHP prototype had good heat sharing characteristics during the operating. Heat load was effectively shared among the evaporators, but the magnitude of heat sharing behaved differently in different heat transfer directions which depend on flow characteristics of each pipeline. It was shown that sharing from lower flow resistance loop to higher flow resistance loop was effective. Instead, when heat was shared to lower resistance loop, the performance of MeLHP would be worse. Such heat sharing made MeLHP prone to failure. Therefore, allocating more heat load in lower flow resistance loop was conducive to heat pipe operation. The heat transfer limit of MeLHP was the same as that of single evaporator loop heat pipe. It was also verified that only one compensation chamber worked when MeLHP was on operation. So the fluid charging ratio of MeLHP should be increased appropriately to obtain equivalent performance with single loop heat pipe. The research is helpful to grasp the operating rules of MeLHP and to promote the practical application of MeLHP.

Key words: multi-evaporator loop heat pipe, heat sharing characteristics, two-phase flow, low temperature, vapor liquid equilibria

摘要：

回路热管（LHP）是柔性高效的两相流换热部件，通过工质的相变以及毛细芯的吸附作用实现高效传热。多蒸发器回路热管（MeLHP）是在其基础上通过多个蒸发器并联实现对多个热源的高效热收集与排散，适用于空间探测技术中多阵列红外探测器的制冷。本文试验样机采用包含三个蒸发器的多蒸发器回路热管结构，管路以气耦合方式并联，管线非对称布置，工作温区为170K，采用乙烷为相变换热工质。以单蒸发器回路热管的数据为参考，在不同的加热功率及加热方式下对多蒸发器回路热管进行运行特性的实验研究，并从补偿器工作特性出发研究其充液率对性能的影响。实验证明，该MeLHP样机运行过程中具有良好的热分享特性，负载热量在各蒸发器间互相分享，且该特性有方向性，与两相流的流动特性相关，表现为低流阻回路向高流阻回路分享为有效分享，反之会引起高流阻性能变差而容易失效，因而低流阻回路分配更多热负载，有利于热管运行；MeLHP的传热极限与单蒸发器回路热管相当，并且实验还验证了MeLHP补偿器的工作方式为单一补偿器工作，因而对MeLHP充装时应适当提高充液率，以获得与单回路热管一致的性能。该研究有助于多蒸发器回路热管运行规律的掌握，对实际应用的推动有促进作用。

关键词: 多蒸发器回路热管, 热分享特性, 两相流, 低温, 气液平衡