横管降膜流动特性与液膜分布规律的数值模拟研究

发布时间：2018-03-01 08:32

本文关键词： 横管降膜流动结构参数流动特性液膜分布数值模拟　出处：《大连理工大学》2016年硕士论文　论文类型：学位论文

【摘要】：横管降膜蒸发冷却技术因其在传热效率、抗管壁结垢和易于排出不凝气体等方面具有的显著优势,加之其能充分利用工业余热和低品位热能,己被广泛应用于大型工业生产和国民生活中,是解决能源消耗过大、排放物污染严重等问题的一种高效能技术。横管管外的液体降膜流动和蒸发冷凝是一个复杂的多相流动与传热传质过程,管外液膜可以看作传热传质发生的载体,其管间流动型态、流体间的相互作用和管外液膜的厚度及分布规律等,都直接影响了整个管束的传热传质情况。本文以海水淡化应用中的横管降膜蒸发技术为背景,借助Fluent软件,采用VOF方法对横管管外的液体流动特性和液膜的铺展分布情况进行了数值模拟研究,以丰富对横管降膜流动中液体在多种因素耦合作用下的动力学规律的研究。本文在阅读了大量相关文献的基础上,针对影响管液体成膜的结构参数,对横管降膜的流动特性和液膜分布进行了较为全面的二维数值模拟,研究了喷淋密度、管间距、入口Re数和管径大小等不同参数下的液膜厚度变化规律,并找出其中影响液膜分布的最主要因素,为三维数值模拟提供一定的参考依据。二维模拟在研究膜状流型时能够获得较好的规律,但不能观察到柱状流型下液膜沿轴向铺展的流动行为。鉴于此,本文重点针对柱状流型下的横管降膜流动过程进行了全三维数值模拟,对液体沿横管轴向的铺展情况和液膜在管外的分布情况进行了细致分析。此外,在确定稳定柱状流型的过程中,本文是以滴柱状过渡流态为临界,并对这种滴状和柱状夹杂出现的管间流型下的液膜流动、铺展规律进行了动力学分析。通过对横管降膜流动的模拟研究发现,液体在管外铺展成膜的情况受到各种外力的叠加作用和液体间的相互作用,液膜沿圆周方向的分布呈现规律性的波动变化。本文的三维数值模拟结果能较好的解释和分析液体的流动特性和成膜规律。单喷淋口下液体会在管外铺展形成“马鞍形”；当液体分别从相邻两喷淋口喷出时,两侧下落液体形成的液膜会沿着轴向交汇融合,并在中间位置形成波峰,液体间的相互作用力使得越靠近波峰位置的液膜厚度越大,两侧液体最终在中间位置附近汇成一个新的液柱并流向下一级管束。相比之下,二维模拟在研究膜状流的液膜流动和分布规律时能给出较好的解释,但不能获得轴向的液膜铺展和流动特性。此外,二维模拟在分析和筛选多种结构参数的影响规律时发挥了高效作用,并为三维模拟提供了重要的参考依据。
[Abstract]:Horizontal tube falling film evaporation cooling technology because of its significant advantages in heat transfer efficiency, anti wall fouling and easy discharge of noncondensable gas and other aspects of the full utilization of industrial waste heat and low grade heat energy, has been widely used in large-scale industrial production and national life, is to solve the problem of energy consumption is too large, a efficient technical problems of emissions pollution. Horizontal tube falling film flow and evaporation condensation is a complex multiphase flow and heat transfer process of liquid film can be regarded as the carrier of mass transfer occurs, the inter tube flow pattern, the interaction between fluid and liquid film thickness and distribution, have a direct impact on the heat and mass transfer. The whole bundle of seawater desalination in the application of horizontal tube falling film evaporation technology as the background, with the help of Fluent software, using VOF method of liquid flow on transverse tube. The distribution and spreading of liquid membrane were studied by numerical simulation, study on the kinetics of liquid tube falling film flow in under coupling action of various factors on the cross to the rich. Based on the basis of reading a lot of literature, the influence of structure parameters for liquid film, liquid film on the flow and distribution of horizontal tube the falling film of two dimensional numerical simulation of a comprehensive study, the spray density, tube spacing, film thickness variation of different parameters of Re entrance number and tube size and under, and find out where the main factors affecting the film distribution, and to provide reference for numerical simulation. The two-dimensional simulation can obtain better regularity in the study of film flow, but cannot observe the flow behavior of liquid film flow along the axial direction of columnar spreading. In view of this, this paper focuses on horizontal tube falling film flow process of columnar regime The three-dimensional numerical simulation, the distribution of the liquid along the horizontal tube axial spreading and liquid film outside the pipe is analyzed in detail. In addition, in the process of determining the stability of columnar patterns, this paper is based on the drop column transition regime is critical, and the mixed liquid flow tube clamp between flow patterns under the the droplet and column, spreading rule of the dynamic analysis. Through simulation research on horizontal tube falling film flow that liquid by the interaction of various forces between superposition and liquid in the tube spreading film, fluctuation of film distribution along the circumferential direction of the three-dimensional numerical. The simulation results of this paper can better explain and analyze the flow characteristics of liquid film and liquid spray mouth under the law. A single experience outside the pipe spreading form "saddle"; when the liquid is ejected from the spray port two adjacent respectively, on both sides of The liquid falling liquid film formed along the axial convergence, and peak is formed in the middle position, the interaction between the liquid film thickness is close to the peak position of the liquid in the middle position, both sides end near the sink into a new liquid column and flow to the next level bundle. In contrast, the two-dimensional simulation of liquid flow and Study on the distribution in the film flows can give a better explanation, but can not get the film spreading axial and flow characteristics. In addition, the two-dimensional simulation plays a role in the efficient effect of different structure parameters and screening analysis, and provides an important reference for three-dimensional simulation.

【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TK124

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