Oxidation effect of copper on the downward-facing flow boiling CHF under atmospheric condition
Oxidation effect of copper on the downward-facing flow boiling CHF under atmospheric condition
复制标题
常压条件下铜对下流沸腾CHF的氧化作用
DOI：
10.1016/j.ijheatmasstransfer.2020.119866
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发表时间：
2020
影响因子：
5.2
通讯作者：
Okamoto Koji
中科院分区：
文献类型：
--
作者：
Wang Kai;Erkan Nejdet;Okamoto Koji
在本研究中，进行了向下流动沸腾实验，以研究铜在大气条件下的氧化效应。将铜表面抛光，然后放入干燥箱中，在300°C下干燥1小时、3小时和6小时。与裸表面相比，在三个质量通量条件下，在氧化的情况下，传热系数的恶化和临界热通量（CHF）的增强被发现。随着质量流量的增加，CHF增强率减小。氧化后，接触角减小。虽然以前的许多研究试图用接触角的变化来解释CHF的增强，但这在下向流沸腾中很难应用。CHF的增强与氧化过程中表面形貌变化引起的形核位密度（NSD）变化有关。氧化后铜表面产生的气泡较少。通过python代码计算了表面上产生的气泡数量，并显示出与CHF的反比关系，并通过模型进行了解释。在较高的热流密度下，蒸汽覆盖面积减小，这是氧化后NSD减少的结果。显微镜图像显示，表面上的空洞的数量减少，这可能是NSD下降的原因。
In the present study, experiments of downward-facing flow boiling were conducted to investigate oxidation effects of copper under atmospheric conditions. The copper surface was polished and then put into a drying oven for a period of 1 h, 3 h and 6 h under 300°C. Compared with a bare surface, a deterioration in the heat transfer coefficient and an enhancement in critical heat flux (CHF) was found in the oxidized case for three mass flux conditions. With the mass flux increasing, the CHF enhancement ratio decreased. After oxidation, the contact angle decreased. Although many previous studies tried to explain the CHF enhancement by the change of contact angle, it was difficult to be applied in the downward-facing flow boiling. The enhancement of CHF was associated with nucleation site density (NSD) change caused by the surface morphology change during oxidation. Fewer bubbles generated on the copper surface after oxidation. The number of bubbles generated on the surface was calculated by a python code and it showed an inverse relationship with CHF, which was explained by a model. Under higher heat flux, the vapor cover area decreased, which was a result of the reduction in NSD after oxidation. Microscope images showed the decrease of the number of cavities on the surface, which was likely to be the reason for the decreasing of NSD.