不同工质下带蒸汽腔的?形微通道热沉特性

Characteristic of an ?-shape microchannel heatsink with different working fluid

借鉴轴向槽道热管结构在工作时良好的气、液分离工作特性,本文提出了一种带蒸汽腔的复合微通道热沉,用以解决大面积或高热流能量收集时热沉通道内部由于排气不畅易导致气塞和返流现象,进而出现流动沸腾不稳定性问题和传热恶化的问题。热沉底板包含20个?形平行通道,肋顶端与盖板下表面间形成连通的蒸汽腔作为两相流时的气体流道。实验以无水乙醇、Novec HFE 7100为工质,并结合可视化观测对热沉性能进行了研究,可以观察到随加热热流密度逐步增加,热沉内部工质依次经强制对流到过冷沸腾、核态沸腾,并最终达到过渡沸腾,可视化实验结果与温度测量结果相吻合。当使用乙醇为工质,在入口质量流速qm=280.37kg/(m2·s)、加热热流密度qeff=30.32W/cm2时,最大传热系数为9494W/(m·℃)。此种结构在有效地保证了热沉换热效果的同时,通过分离气、液流道对抑制流动沸腾不稳定性有明显效果。

A hybrid microchannel/grooved heat pipes heatsink was designed based on excellent characteristics of gas and liquid flow separation in axial grooved heat pipes at work. The heatsink contains 20 Ω-shape parallel channels on the substrate, and the zone between top sides of the ribs and the bottom side of the glass cover plate forms a vapor chamber in boiling condition. The structure was designed to remit the instability boiling problems such as gas plunger and vapor return symptoms in large-size or high heat flux dissipation conditions. The experiments were divided into two main parts：visualization experiments and heat transfer performance test with the usage of a digital camera and a data acquisition system. Absolute ethyl alcohol and 3 M Novec HFE 7100 electronic coolant were used as working fluid in all experiments. The two variables of effective input heat flux qeff and mass flux qmwere respectively controlled by voltage and electric current of the direct-current source and indirectly controlled by the control voltage of the micro gear pump. The range of qeff was 0—30.32 W/cm2 and the range of qm was 280.37（534.5）—533.26（807.22）kg/（m2·s） for C2 H5 OH（HFE 7100）. To maintain same coolant properties, the inlet fluid temperature was kept at 20℃ by the cooling machine. Visualization experiments indicated that the boiling regimes from onset boiling state in low heat flux to nuclearboiling match well with the measuring temperature. The experimental results showed that, when q2 m=280.37 kg/（m2·s）、qeff=30.32 W/cm, the max heat transfer coefficient is 9494 W/（m·℃）;the coolant vapor can easily escapes from the top side of channels in fully developed boiling condition so that this design can control the instability boiling problems caused by vapor plunger effectively.