To solve the heat dissipation problem of high heat flux components on spacecraft, experiments were carried out to investigate the flow boiling heat transfer characteristics of ammonia in a microchannel heat sink. Verified by gravity-independent criteria, the experimental results can be used to predict the performance of flow boiling heat transfer in microgravity environment. The heat sink consisted of 37 V-shaped microchannels with hydraulic diameters of 280 μm and channel lengths of 45 mm. Saturated flow boiling experiments were conducted with heat fluxes of 60.2~134.3 W/cm², mass fluxes of 165~883 kg/m²s and saturation temperatures of 25 and 35 °C, as well as subcooled flow boiling experiments with inlet subcooling of 5 °C as a comparison. According to the experimental results, the following conclusions can be drawn. (1) As the mass flow rate increases, higher wall superheat is needed to trigger nucleate boiling. (2) In a lower mass flux range, the heat transfer coefficient changes drastically with mass flux, showing convective boiling characteristics, while the value varies slightly in a higher mass flux range, indicating that the nucleate boiling mechanism is dominant. (3) Under the experimental conditions in this work, the average heat transfer coefficient of ammonia reaches its peak when the outlet vapor quality is between 0.21 and 0.31. (4) A subcooled inlet condition has a suppression effect on the average heat transfer capacity of the working fluid at high mass flux, and increasing the saturation temperature reduces the average heat transfer coefficient. In addition, a comparison between the experimental results and existing correlations demonstrated that the correlation proposed by Fang predicted the experimental results well, and then a modified Fang correlation was proposed based on the experimental data obtained in this study. The results could provide references for the prediction of flow boiling heat transfer performance in aerospace environments and the design of heat dissipation systems.

中文翻译：

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微通道氨流沸腾传热特性的实验研究

为了解决航天器上高热通量的散热问题，进行了实验研究微通道散热器中氨的流沸腾传热特性。通过与重力无关的标准验证，实验结果可用于预测微重力环境下流沸腾传热的性能。散热器由37个V形微通道组成，其水力直径为280μm，通道长度为45 mm。进行60.2〜134.3 W / cm ^2的热通量，165〜883 kg / m ^2的质量通量的饱和流沸腾实验s和饱和温度分别为25和35°C，以及过冷流动沸腾实验（入口过冷为5°C作为比较）。根据实验结果，可以得出以下结论。（1）随着质量流量的增加，需要更高的壁过热来触发核沸腾。（2）在较低的质量通量范围内，传热系数随质量通量而急剧变化，表现出对流沸腾特性，而在较高的质量通量范围内传热系数略有变化，表明成核沸腾机理占主导地位。（3）在这项工作的实验条件下，当出口蒸气质量在0.21和0.31之间时，氨的平均传热系数达到峰值。（4）过冷的入口条件对高质量通量下的工作流体的平均传热能力具有抑制作用，并且增加饱和温度会降低平均传热系数。另外，通过对实验结果与现有相关性的比较，表明方提出的相关性很好地预测了实验结果，然后根据本研究获得的实验数据提出了修正的方相关性。研究结果可为航空航天环境下沸腾传热性能的预测和散热系统的设计提供参考。实验结果与现有相关性的比较表明，Fang提出的相关性很好地预测了实验结果，然后根据本研究获得的实验数据提出了改进的Fang相关性。研究结果可为航空航天环境下沸腾传热性能的预测和散热系统的设计提供参考。实验结果与现有相关性的比较表明，Fang提出的相关性很好地预测了实验结果，然后根据本研究获得的实验数据提出了改进的Fang相关性。研究结果可为航空航天环境下沸腾传热性能的预测和散热系统的设计提供参考。