含功能涂层分割壁面降液膜流动过程的数值模拟

发布时间：2018-06-29 22:50

  本文选题：CFD + 功能涂层　； 参考：《大连理工大学》2015年硕士论文

【摘要】：雾霾的肆虐将节能减排提上了全新的高度。能够回收工业余热,提高能源利用率的热泵技术正逐步走进人们的视野。吸收器是热泵的核心设备,对于提高热泵的转化效率起到了决定性作用。竖管吸收器由于占地面积小、结构简单等优点应用前景广泛。研究竖管吸收器内的降液膜流动机理,以提高热泵性能,成为当前的热点话题。本文希望通过数值模拟软件,在降液膜流动壁面上添加疏水涂层构型,从而构成功能涂层分割壁面,研究亲疏水组合壁面对降液膜流动过程的影响。建立含功能涂层的二维竖直壁面降液膜流动模型,利用VOF方法对最小喷淋密度定义式进行了验证。以最小喷淋密度为界,分别模拟了喷淋密度小于最小喷淋密度和喷淋密度大于最小喷淋密度时有无涂层的降液膜流动行为：对于喷淋密度小于最小喷淋密度的情况,壁面上会出现干斑,流至涂层区域的降液膜会发生积聚现象,在降液膜内部出现涡流,对于传热传质过程有利；实际的工业操作大都是喷淋密度大于最小喷淋密度的情况,降液膜会将壁面完全覆盖,降液膜内部并无涡流产生。通过分析流动稳定后有无涂层时降液膜的波动形态,结合湍动强度的概念引入变异系数,利用统计分析的方法对降液膜内部的扰动情况进行分析比较。由于二维模型简化了液相入口宽度方向,使得该方向上的波动情况无法判断,因此结合已有文献建立了含功能涂层三维竖直壁面降液膜流动模型。通过模拟计算,其与二维模型的结论吻合良好,同时也分析比较了降液膜流动稳定后有无涂层时沿液相入口宽度方向上的扰动情况。给定特定的喷淋密度,在流动稳定后,有涂层时壁面特定位置处垂直于流动方向上的速度分量较无涂层时大,并且二维和三维模拟得到的垂直于流动方向上速度分量的变异系数也是有涂层时大,这都表明涂层区域的存在能增强降液膜内部的扰动效果。对于二维模型,分别设置涂层的接触角为70。(无涂层)、100。、120。、150。,涂层区域的长度为0mm(无涂层)、5mm、l0mm、15mm,也得到了相同的结论。但也发现并不是涂层的接触角越大越好,也不是涂层区域的长度越长越好。对于特定的模型,寻求一个最优的涂层接触角和涂层区域长度仍有待进一步的研究。模型的建立都经过了Nusselt理论的验证,得到的结论与已有的高温竖直管外降液膜吸收器得到的结论吻合,也说明了本文模拟的正确可靠。
[Abstract]:The haze raging will save energy and reduce emissions to a new height. Heat pump technology, which can recover industrial waste heat and improve energy efficiency, is gradually coming into people's field of vision. Absorber is the core equipment of heat pump, which plays a decisive role in improving the conversion efficiency of heat pump. The vertical tube absorber has a wide application prospect because of its small area and simple structure. In order to improve the performance of heat pump, it has become a hot topic to study the mechanism of falling liquid film flow in vertical tube absorber. In this paper, the hydrophobic coating configuration is added to the flow wall of down-liquid film by numerical simulation software, and the effect of hydrophilic composite wall on the flow process of down-liquid film is studied. A flow model of two dimensional vertical wall falling liquid film with functional coating was established and the definition of minimum spray density was verified by VOF method. Taking the minimum spray density as the boundary, the flow behavior of the falling liquid film with or without coating when the spray density is less than the minimum spray density and the spray density is greater than the minimum spray density is simulated, respectively: for the case where the spray density is less than the minimum spray density, There will be dry spots on the wall, the falling liquid film flowing to the coating area will accumulate, and the eddy current will appear inside the falling liquid film, which is beneficial to the heat and mass transfer process. The actual industrial operation is mostly the case that the spray density is larger than the minimum spray density. The falling liquid film will cover the wall completely, and there will be no eddy current inside the falling liquid film. By analyzing the fluctuation pattern of the falling film when the flow is stabilized or not, and combining the concept of turbulent intensity, the variation coefficient is introduced, and the disturbance inside the falling liquid film is analyzed and compared by the statistical analysis method. Since the two-dimensional model simplifies the direction of the inlet width of the liquid phase, it is impossible to judge the fluctuation in this direction. Therefore, a three-dimensional down-flow model with functional coating on vertical wall is established. The simulation results show that it is in good agreement with the conclusion of the two-dimensional model, and the disturbance along the direction of the inlet width of the liquid phase is also analyzed and compared. Given a specific spray density, the velocity component perpendicular to the flow direction at a particular position on the wall with a coating is larger than that without the coating after the flow is stabilized. The coefficient of variation of velocity component perpendicular to the flow direction obtained by 2D and 3D simulation is also large, which indicates that the existence of coating region can enhance the disturbance effect inside the falling liquid film. For the two-dimensional model, the contact angle of the coating is 70. The length of the coating area is 5mm / 10mm / 15mm, and the length of the coating area is 5mm / 10mm / 15mm. The same conclusion is obtained. However, it is also found that the larger the contact angle of the coating is, the better the length of the coating area is. For the specific model, the search for an optimal contact angle and the length of coating area still needs further study. The establishment of the model is verified by Nusselt theory, and the results are in agreement with those obtained by the existing downfall membrane absorber of high temperature vertical tube, which also shows that the simulation in this paper is correct and reliable.
【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】：TQ021.1

【共引文献】

中国期刊全文数据库 前4条

1 贾晓东;刘永文;李龙;苏明;;格子Boltzmann方法的竖壁汽液降膜数值研究[J];动力工程学报;2014年10期

2 胡剑光;于建国;戴干策;;狭通道内气液逆流时液膜波动及其与填料塔液泛的关系[J];华东理工大学学报(自然科学版);2014年01期

3 陈世昌;马建平;张先明;陈文兴;;竖直降液膜流动在反应工程中的应用[J];化工进展;2014年10期

4 黄小龙;胡国辉;;低雷诺数下沿正弦壁面下落液体薄膜的频谱特性[J];上海大学学报(自然科学版);2014年02期

中国重要会议论文全文数据库 前1条

1 陈世昌;张先明;马建平;王飞;陈文兴;;高黏流体在波形外壁的降液膜流动及其表面更新[A];2015年中国化工学会年会论文集[C];2015年

中国博士学位论文全文数据库 前3条

1 张永良;离心喷嘴雾化特性实验研究和数值模拟[D];中国科学院研究生院（工程热物理研究所）;2013年

2 郝兆龙;高温吸收式热变换器热力学和传递性能研究[D];大连理工大学;2013年

3 罗林聪;水平异形管降膜蒸发流动与传热强化机理及实验研究[D];山东大学;2014年

中国硕士学位论文全文数据库 前7条

1 武晓伟;垂直管外降膜流动特性及布膜装置的研究[D];郑州大学;2013年

2 魏彪;列管式降膜蒸发器加热管内钢丝螺旋防垢技术研究[D];湘潭大学;2012年

3 张强;降膜式吸收器关键技术的基础研究[D];陕西理工学院;2013年

4 刘佳特;规整填料结构开发的数值模拟与实验研究[D];华东理工大学;2014年

5 朱永欣;非平整基底上液膜流动的数值模拟研究[D];华北电力大学;2014年

6 贾晓东;基于格子Boltzmann方法的液滴与液膜两相流动数值模拟[D];上海交通大学;2014年

7 贾莹;压力旋流式喷嘴干涉的数值模拟[D];大连理工大学;2014年

，

本文编号：2083688