表面润湿性及重力协同控制下的冷凝流动特性

发布时间：2018-02-01 03:49

本文关键词： 倾斜管表面润湿性混合蒸汽协同作用　出处：《大连理工大学》2015年硕士论文　论文类型：学位论文

【摘要】：蒸汽冷凝现象广泛应用于各种工业生产中,例如空调系统、制冷技术、汽车产业以及很多其他的过程工业。如何高效能利用能源、强化传热的效率,是研究者们长期关注和研究的问题。一般对于冷凝传热的强化可以从两个角度考虑：一是增加扩展表面,即对管的表面作出结构上的变化,常见的有翅片管、螺旋管和波纹管等；二是改变表面润湿性,通常可以通过处理固体表面来实现,增大蒸汽冷凝液滴在固体壁面上的表观接触角,使之形成滴状冷凝,进而强化了固液间的传热性能。本文结合表面改性的方法改变其表面润湿性,探究倾斜角度和不凝气对蒸汽冷凝传热的影响,对不同倾斜角度的管外蒸汽冷凝强化提供一定的参考,为其在工程中的实际应用给予数据支持。首先搭建了倾斜管外混合蒸汽冷凝的实验装置,并验证实验系统的热平衡,利用分子自组装膜的方法在紫铜管表面制备了十八烷基硫醇疏水表面及经过氧化刻蚀的十八烷基硫醇超疏水表面。实验考察了在纯蒸汽和含10%不凝气的混合蒸汽条件下,不同倾斜角度的疏水和超疏水表面的冷凝流动及传热特性,实时监测并采集测试温度和压力值,计算冷凝传热数据,并通过高速摄像仪从不同拍摄位置对液滴冷凝形态和流动特性进行观测和分析。实验数据显示：处于铜管不同位置的液滴具有不同程度的接触角滞后,且影响较大；在含10%不凝气的混合蒸汽条件下,疏水表面不同位置液滴的接触角滞后程度均小于纯蒸汽条件下；对于铜管不同的倾斜角度,其接触角滞后均在一定程度上具有随着倾斜角度的增大而减小的变化趋势；在疏水表面条件下,液滴的脱落直径随着倾斜角度的增大而减小；在超疏水表面条件下,液滴的脱落直径随着倾斜角度的增大而增大；冷凝液对超疏水表面的冲刷周期均大于疏水表面,当表面润湿性相同,混合蒸汽条件下的表面冲刷周期均大于纯蒸汽条件下的冲刷周期。对于不同倾斜角度的疏水表面,在相同表面过冷度时,随着倾斜角度的增大,管外传热系数近似相等,稍有减小的趋势；对于纯蒸汽超疏水表面,倾斜角度为0。、30。和45。时,其传热性能近似相等,在60。时传热性能出现较大值。
[Abstract]:Steam condensation is widely used in various industrial production, such as air conditioning system, refrigeration technology, automobile industry and many other process industries. Generally, the enhancement of condensation heat transfer can be considered from two aspects: one is to increase the expansion surface, that is, to make structural changes on the surface of the tube, and the common one is finned tube. Spiral tube and bellows, etc.; The other is to change the wettability of the surface, which can be realized by treating the solid surface, increasing the apparent contact angle of the steam condensing liquid drop on the solid wall and forming the droplet condensation. Furthermore, the heat transfer performance between solid and liquid is enhanced. In this paper, the surface wettability is changed with the method of surface modification, and the influence of inclined angle and non-condensed gas on the heat transfer of steam condensation is investigated. It provides a certain reference for the outside steam condensation strengthening of different inclined angles, and provides data support for its practical application in engineering. Firstly, an experimental device for condensing mixed steam outside the inclined tube is built. The thermal balance of the experimental system is verified. The hydrophobic surface of 18 alkyl mercaptan and the superhydrophobic surface of 18 alkyl mercaptan etched by oxidation were prepared on the surface of copper tube by molecular self-assembly film. The mixture of pure steam and uncondensed gas containing 10% was investigated experimentally. Steam. The condensing flow and heat transfer characteristics of hydrophobic and superhydrophobic surfaces with different inclined angles were monitored and measured in real time to calculate the condensation heat transfer data. The condensing morphology and flow characteristics of the droplet are observed and analyzed by high-speed camera from different shooting positions. The experimental data show that the droplets in different positions of copper tube have different contact angle lag. And the influence is great; Under the condition of mixed steam containing 10% uncondensed gas, the contact angle hysteresis of droplets at different positions on the hydrophobic surface is lower than that of pure steam. For the different inclined angles of copper tubes, the contact angle lag has the tendency of decreasing with the increase of the inclined angle to a certain extent. Under hydrophobic surface conditions, the drop diameter of droplets decreases with the increase of inclined angle. Under the condition of superhydrophobic surface, the drop diameter of droplets increases with the increase of inclined angle. The scouring period of superhydrophobic surface of condensate is longer than that of hydrophobic surface, and the wettability of superhydrophobic surface is the same. For hydrophobic surfaces with different inclined angles, the surface scour periods under mixed steam conditions are larger than those under pure steam conditions. The heat transfer coefficient outside the tube is approximately equal, with a slight decreasing trend. For the superhydrophobic surface of pure steam, the heat transfer performance of the superhydrophobic surface is approximately equal when the inclination angle is 0.30 and 45.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ026.2

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