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Visualization experiments on the condensation process in heat pipe wicks

机译:热管芯冷凝过程的可视化实验

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Visualization experiments are conducted to explore the condensation process in sintered copper wicks of operating flat-plate heat pipes. Two working fluids, water and methanol, and two wick types, mesh and powder wicks, are investigated. The effect of non-condensable gas has been carefully controlled at an insignificant level. The steady-state condenser resistances R_c and the evaporator resistances R_e are measured at incremented heat loads Q. For water, cyclic dropwise condensation is observed on exposed wick tops due to the finite water/copper contact angle. For methanol, the condenser is submerged in the liquid as a result of zero contact angle and ineffective liquid delivery out of the condenser. This leads to quiescent methanol condensation with higher R_cs. For all the tests, R_cs(in Kcm~2/W)are several times larger than R_cs. The main reasons are the thicker liquid layer in the condenser wick and the large thermal resistance associated with the condensed liquid layer, with the latter dominating. Considerable under-prediction of R_c may exist in current theoretical models which simply applies the conduction-limit model without considering the thermal resistance from the condensed-liquid layer.
机译:进行了可视化实验,以研究运行的平板热管的烧结铜芯中的冷凝过程。研究了两种工作流体:水和甲醇,以及两种芯吸类型:网状和粉末芯吸。不可冷凝气体的影响已被谨慎地控制在很小的水平上。在增加的热负荷Q下测量稳态冷凝器电阻R_c和蒸发器电阻R_e。对于水,由于有限的水/铜接触角,在裸露的灯芯顶部观察到了周期性的滴状冷凝。对于甲醇,由于零接触角和无效的液体从冷凝器中排出,冷凝器浸没在液体中。这导致R_cs较高的静态甲醇缩合。对于所有测试,R_cs(以Kcm〜2 / W为单位)比R_cs大几倍。主要原因是冷凝器油芯中的液体层更厚,以及与冷凝液层相关的较大的热阻,其中后者占主导。当前的理论模型中可能存在相当大的R_c预测不足,这些理论模型仅应用了传导极限模型,而没有考虑来自冷凝液层的热阻。

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