中文摘要：

含不凝气的混合蒸汽冷凝广泛存在于化工、石油、电力和海水淡化等领域.在空气环境下超疏水表面具有较大的接触角,有可能实现冷凝强化传热的目的.但在纯蒸汽冷凝环境中,液滴会完全润湿超疏水表面的微纳结构,使表面的超疏水性＂失效＂.而在含不凝气的混合蒸汽冷凝过程中,若不凝气充满超疏水表面的微纳结构,液滴呈Cassie或过渡态润湿模式,保持或部分保持表面的超疏水特性.对于倾斜表面,冷凝液滴的脱落直径和冲刷周期都会发生变化,进而影响冷凝传热.因此,深入认识混合蒸汽在不同倾斜角的超疏水竖管表面上的冷凝特性,分析液滴的运动特性,对探究冷凝机理和研发先进强化传热技术有重要意义.本文利用氧化刻蚀-自组装的方法制备了紫铜管超疏水表面,系统地研究了不同倾斜角度时混合蒸汽冷凝过程中液滴的接触角滞后、临界脱落直径以及冲刷周期,并与纯蒸汽、疏水表面的情况进行了对比.结果表明,在铜管顶部（沿铜管圆周方向）,超疏水表面冷凝时接触角滞后小于疏水表面,而在铜管中部和底部超疏水表面的接触角滞后则较大;在超疏水表面条件下,液滴的脱落直径随着倾斜角度的增加而增大;冷凝液对超疏水表面的冲刷周期均大于疏水表面,且随着倾斜角增加,冲刷周期略有减小.

英文摘要：

Steam condensation with non-condensable gas exists widely in petro-chemical, power plant and seawater desalination processes. Super-hydrophobic surfaces with high contact angle could be an promising condensing surface to promote DWC and enhance heat transfer. As pure steam condensing droplet completely occupies micro/nano-structures of super-hydrophobic surfaces, super-hydrophobic function becomes ＂invalid＂. For stream-air mixture vapor, the non- condensable gas would occupy the micro/nano-structures instead of water. Droplets form Cassie or transition wetting mode, holding or partly holding super-hydrophobic feature. Inclination angle of the tube can influence the shape, size and dynamic characteristics of the condensing droplets, thus changing the heat transfer performance. Therefore, for getting deeply insights of the effect of the non-condensable gas on condensation heat transfer, it is necessary to study the condensing drops characteristics on super-hydrophobic tube for different inclined angles. According to dropwise condensation model, increasing contact angle hysteresis, departure droplet size, sweeping period would reduce the condensation heat transfer efficiency. In this paper, dropwise condensation is performed on super-hydrophobic copper tube, departure droplet size, sweeping period and the phenomenon of contact angle hysteresis are thoroughly studied and are compared with the case of hydrophobic surface or pure steam to explore the influence of inclined angle and surface wettability on droplet dynamics to achieve condensation heat transfer enhancement. The experimental result shows： （1） On the top of copper tube, for the condensation of steam with 10% non-condensable gas, the contact angle hysteresis on super-hydrophobic surface is smaller than that on hydrophobic surface. Compared with pure steam condensation on super-hydrophobic surface, the contact angle hysteresis of mixed steam is smaller because the non- condensable gas fills the micro/nano-structures. However, on the middle and bo