倾斜超疏水管外滴状冷凝液滴特性的可视化

发布时间：2019-04-17 19:31

【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.
[Abstract]:Mixed steam condensing with non-condensing gas exists widely in chemical, petroleum, power and seawater desalination fields. The superhydrophobic surface has a large contact angle in the air environment, so it is possible to achieve the purpose of condensation enhancement of heat transfer. But in pure steam condensing environment, the droplets will completely wetten the micro / nano structure of the superhydrophobic surface and make the superhydrophobicity of the surface "invalid". In the process of mixing steam condensation with non-condensing gas, if the non-condensing gas is filled with the micro / nano structure of superhydrophobic surface, the droplets exhibit Cassie or transitional wetting mode, and the superhydrophobicity of the surface is maintained or partially maintained. For the inclined surface, the drop diameter and scour period of the condensate droplets will change, which will affect the condensation heat transfer. Therefore, it is of great significance to understand the condensation characteristics of mixed steam on the surface of superhydrophobic vertical tubes with different inclination angles and to analyze the motion characteristics of droplets, which is of great significance to the investigation of condensation mechanism and the development of advanced heat transfer enhancement techniques. In this paper, the super-hydrophobic surface of copper tube was prepared by oxidation etching-self-assembly method. The contact angle lag, critical shedding diameter and scour period of the droplets in the condensation process of mixed steam at different tilt angles were systematically studied. The condition of the hydrophobic surface is compared. The results show that the contact angle lag of the superhydrophobic surface is smaller than that of the hydrophobic surface at the top of the copper tube (along the circumferential direction of the copper tube), while the contact angle lag of the superhydrophobic surface in the middle and bottom of the copper tube is larger. Under the condition of superhydrophobic surface, the diameter of droplet shedding increases with the increase of tilt angle, and the scour period of condensate on superhydrophobic surface is larger than that of hydrophobic surface, and the scour period decreases slightly with the increase of tilt angle.
【作者单位】：大连理工大学化学工程研究所辽宁省化工资源清洁利用重点实验室;
【基金】：国家自然科学基金重点项目(51236002)资助
【分类号】：O35

【相似文献】