多组分液滴降压环境下相变传热传质过程数值模拟

发布时间：2018-03-23 16:33

本文选题：多组分　切入点：液滴　出处：《华北电力大学》2015年硕士论文

【摘要】：本文研究降压环境下多组分液滴的蒸发特性以及水滴闪蒸的气泡生长过程。多组分液滴在降压环境下的蒸发特性可应用于海水淡化、航空航天的液体排放等领域,对该问题的研究有助于掌握多组分相变的传热传质规律。多组分液滴蒸发涉及到液滴表面的瞬时传热,多组分相变,以及组分间的传质扩散,蒸发过程中,液滴内部组分浓度不断变化,增加了问题的复杂性。本文采用理论研究方法,构建多组分液滴降压蒸发模型,通过与已有的实验数据相对比,结果吻合较好,验证了模型的有效性。主要研究内容有:(1)降压环境下盐水液滴蒸发过程理论研究。基于能量守恒方程和传质扩散方程,建立了盐水液滴降压蒸发模型,描述了液滴内部温度分布和浓度分布随时间的变化。考虑盐水浓度对质量蒸发率的影响引入了活度系数。通过数值计算,掌握了蒸发过程中液滴内部温度分布、浓度分布以及液滴无量纲尺寸随时间的变化问题,分析了影响盐水液滴降压蒸发过程的主要因素。(2)降压环境下盐水液滴蒸发析盐过程理论研究。随蒸发过程的进行,当盐水液滴的浓度大于相应温度下的饱和浓度后,液滴表面开始析盐。采用“四阶段模型”,考虑液滴表面的盐壳形成过程,析盐过程的结晶热释放,以及析出盐分对盐水液滴蒸发特性的影响,研究盐水液滴在降压环境下析盐过程的温度变化。(3)双组分酒精溶液液滴降压蒸发过程理论研究。酒精溶液液滴内包含两种可挥发性成分,蒸发过程中两种组分相互影响,采用“双组分液滴蒸发模型”,引入不同组分的活性因子,考虑液滴表面的质量蒸发率。通过数值计算,掌握了蒸发过程中,液滴内部浓度分布、温度分布以及液滴无量纲尺寸随时间的变化问题,分析了影响酒精溶液液滴在降压蒸发过程中温度及尺寸变化的主要因素。(4)速降压环境下,液滴闪蒸伴随的气泡生长过程也是影响闪急喷雾的重要组成部分,本文对水滴闪蒸的气泡生长过程进行了理论研究。在Schrage液滴闪蒸模型的基础上,引入气泡生长的动力学方程式(Rayleigh方程式),通过数值计算,分析了影响气泡生长的主要因素。
[Abstract]:In this paper, the evaporation characteristics of multi-component droplets and the bubble growth process of water droplet flash are studied. The evaporation characteristics of multi-component droplets in the pressure lowering environment can be used in desalination of seawater, liquid discharge in aerospace, and so on. The study of this problem is helpful to understand the heat and mass transfer law of multi-component phase change. The evaporation of multi-component droplets involves the instantaneous heat transfer on the surface of the droplet, the multi-component phase transition, the mass transfer and diffusion between components, and the process of evaporation. In this paper, a multi-component droplet depressurization evaporation model is constructed by theoretical research method, and the results are in good agreement with the available experimental data. The validity of the model is verified. The main contents of this study are: 1) theoretical study on the evaporation process of saltwater droplets in a pressurized environment. Based on the energy conservation equation and mass transfer diffusion equation, a saltwater droplet depressurization evaporation model is established. The variation of temperature distribution and concentration distribution with time in droplet is described. The activity coefficient is introduced into account of the influence of salt water concentration on mass evaporation rate. The distribution of concentration and the dimensionless size of droplets vary with time. The main factors affecting the process of saltwater droplet depressurization and evaporation are analyzed. When the concentration of the saltwater droplet is higher than the saturation concentration at the corresponding temperature, the surface of the droplet begins to salting-out. The "four-stage model" is used to consider the formation process of salt shell on the droplet surface, and the crystallization heat is released during the salt-evolution process. And the effect of precipitated salts on the evaporation characteristics of saltwater droplets, This paper studies the temperature change of salt-evolution process of saltwater droplets under depressurization environment. The theoretical study of two-component alcohol solution droplet depressurization evaporation process is carried out. There are two volatile components in the droplet of alcohol solution, and the two components interact with each other in the evaporation process. The two-component droplet evaporation model was used to introduce the active factors of different components, and the mass evaporation rate of the droplet surface was taken into account. Through numerical calculation, the internal concentration distribution of the droplet in the evaporation process was grasped. The temperature distribution and droplet dimensionless size change with time are analyzed. The main factors affecting the temperature and size change of droplet in alcohol solution during the process of depressurization and evaporation are analyzed. The bubble growth process accompanied by droplet flash is also an important component of flash spray. The bubble growth process of water droplet flash is theoretically studied in this paper. The dynamic equation of bubble growth is introduced into Rayleigh equation. The main factors affecting bubble growth are analyzed by numerical calculation.
【学位授予单位】：华北电力大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TK124

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