基于移动网络的超滤膜污染物截留过程动态数值模拟研究

发布时间：2018-04-26 14:14

本文选题：超滤 + 膜污染　；参考：《西安建筑科技大学》2015年硕士论文

【摘要】：在膜组件的运行过程中,膜污染一直是制约膜技术发展和应用的主要问题之一,有效解决膜污染的问题是优化膜组件的运行条件、延长膜组件运行周期的关键,而研究膜污染的机理、充分认识膜污染的过程则是这一问题的核心。由于影响膜污染过程的因素众多,实验及理论研究均是不可或缺的研究手段。由于受到测量手段及成本的制约,实验手段通常无法对膜污染问题开展精细化、大范围的研究,这就需要结合强有力的数学模型,来获得对这一问题深入、全面的认识。近年来,已出现了大量基于计算流体动力学(Computational Fluid Dynamics,CFD)的有关膜过滤过程的模拟及优化工作,通过数值模拟不但可以直观地获得膜组件内的各种流动参数,还可以对膜组件的过滤特性及运行条件进行优化,甚至在某些无法开展实验研究的场合也可以通过CFD手段获得有价值的信息。目前有关膜污染的数值模拟研究主要集中在对流场、浓度场分布的研究,以及稳态或准稳态情况下污染物的截留、洗脱过程研究。但由于膜污染过程是复杂的多物理场共同作用的动态变化过程,因此区别于现有的分析解及计算流体力学模拟手段,本文针对超滤膜组件的膜污染问题,建立了基于移动网格的CFD研究手段。将膜本体视为多孔介质处理,在物理模型中耦合了自由流动、多孔介质流动及稀物质传递过程,并将污染物的法向截留积累量及切向剪切洗脱量与污染物界面处的网格变形速度相关联,实现了对截留污染物在膜面累积过程的动态模拟。通过数值模拟得到了内压式中空纤维超滤膜组件流场和浓度场的分布情况,以及膜表面的浓差极化现象。随后通过中空纤维膜组件的实验,确定出了这一关联表达式中的匹配参数,当污染物截留匹配参数1为2003/mol、剪切力匹配参数2为5×10-15m时,模拟数值结果与两组实验数据均较为吻合,在确定这一参数后,可以此为基础开展同一类型的污染物截留研究。之后在所建立的动态模型的基础上,进一步研究了不同膜面形式(平面膜及波状膜)对膜过滤过程的影响,研究表明平面膜的剪切力分布较均匀,一段时间后膜通量显著下降;而波状膜特殊的形状使得其波峰、波谷处剪切力分布不均匀,从而具有更好的抗污染性能,能够长时间保持一定的过滤通量。这一动态模型的建立为深入地研究污染物的截留过程、开展膜组件的优化设计提供了有效手段。
[Abstract]:Membrane fouling is one of the main problems that restrict the development and application of membrane technology in the process of membrane assembly operation. The key to optimize the operation conditions and prolong the operation period of membrane assembly is to solve the problem of membrane fouling effectively. Studying the mechanism of membrane fouling and fully understanding the process of membrane fouling is the core of this problem. Because there are many factors affecting membrane fouling process, both experimental and theoretical research are indispensable means. Due to the limitation of measurement means and cost, experimental methods are usually unable to carry out a detailed and extensive study on membrane fouling, which requires a strong mathematical model to obtain a thorough and comprehensive understanding of this problem. In recent years, there have been a lot of simulation and optimization work on membrane filtration process based on Computational fluid Dynamics (CFD) and Computational Fluid Dynamics (CFDs). The filtration characteristics and operating conditions of membrane components can also be optimized, and valuable information can be obtained by means of CFD even in some cases where experimental research cannot be carried out. At present, the numerical simulation of membrane fouling mainly focuses on the flow field, concentration field distribution, and the retention and elution process of pollutants in steady or quasi-steady state. However, the membrane fouling process is a complex dynamic process of multi-physical field interaction, so different from the existing analytical solutions and computational fluid dynamics simulation methods, this paper aims at the membrane fouling of ultrafiltration membrane assembly. The research method of CFD based on mobile grid is established. The membrane body is treated as a porous medium, and the free flow, porous media flow and dilute material transfer process are coupled in the physical model. The normal retention accumulation and tangential shear elution of pollutants were correlated with the grid deformation velocity at the pollutant interface, and the dynamic simulation of the accumulation process of the contaminants on the membrane surface was realized. The distribution of flow field and concentration field and the concentration polarization on the membrane surface were obtained by numerical simulation. Then the matching parameters of the correlation expression are determined by the experiment of hollow fiber membrane module. When the pollutant retention matching parameter 1 is 2003 / mol and the shear force matching parameter 2 is 5 脳 10 ~ (-15) m, the simulation results are in good agreement with the two groups of experimental data. After this parameter is determined, the same type of pollutant interception can be carried out on this basis. On the basis of the established dynamic model, the effects of different membrane forms (flat and wave membrane) on the membrane filtration process were further studied. The results showed that the shear force distribution of the membrane was more uniform, and the membrane flux decreased significantly after a period of time. The special shape of the wave-like membrane makes the wave peak and trough shear stress distribution uneven, so it has better anti-pollution performance and can maintain a certain filtration flux for a long time. The establishment of this dynamic model provides an effective means for studying the interception process of pollutants and optimizing the design of membrane modules.
【学位授予单位】：西安建筑科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：X703

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