折板膜组件减缓正渗透外浓差极化的研究

发布时间：2018-03-18 08:42

本文选题：正渗透　切入点：外浓差极化　出处：《大连理工大学》2016年硕士论文　论文类型：学位论文

【摘要】：正渗透是一种新兴水处理技术,因具有能耗低、耐污染、水回收率高等优势,在污水处理、海水淡化等领域有着广泛的应用前景。但浓差极化现象严重降低了正渗透过滤效率。本文针对其中的外浓差极化问题,将折板结构引入到正渗透膜组件的设计中,使廊道沿流动方向呈波浪形,以促进廊道内涡流的产生与发展,从而减缓外差极化。文中采用实验测试和流体力学计算的方法,对折板膜组件性能和作用机理进行了研究。将折板膜组件与传统的平板膜组件进行对比测试,以平板膜组件为基准,评估折板膜组件减缓外浓差极化的性能表现。实验表明,折板能够减缓外浓差极化,具体表现为提高水通量。2M氯化钠溶液为汲取液,去离子水作原料液时,活性层朝向原料液和活性层朝向汲取液两种运行模式下,水通量提升幅度分别为17.45%和18.55%。2 M氯化钠溶液为汲取液,0.5 M氯化钠溶液作原料液时,对应值为分别为15.97%和17.12%。与此同时,折板形状对正渗透膜的选择性无明显不利影响。折板膜组件的形状影响水通量提升幅度,较大波形角度和较小的波长,均有利于水通量的提高。雷诺数影响折板膜组件性能,雷诺数小于800时,雷诺数越大,水通量提升幅度越大；雷诺数大于800时,水通量提升幅度随雷诺数增大略微下降。原料液和汲取液浓度影响浓差极化程度,进而影响折板膜组件减缓外浓差极化的性能表现；汲取液浓度较高或原料液浓度较低时,水通量较大,水通量提升幅度也较大。折板膜组件不能有效减轻内浓差极化。膜污染与浓差极化共存时,折板膜组件能够减缓膜污染,提高水通量。采用计算流体力学软件Fluent,对膜组件单侧廊道内流动特征进行分析。结果表明平板膜组件内流动相对稳定,无涡流出现,流体完全沿x轴方向流动：折板膜组件能够促进廊道内涡流的产生,同时提升壁面剪切力。折板结构通过引入涡流改善了水力条件,提升了水通量。折板膜组件的形状影响廊道内的流动特征,波长较小、波形角度较大时,廊道内涡流较强,壁面剪切力较大。雷诺数也会影响廊道内的流动特征,雷诺数较大时,折板模组件内涡流较强,壁面剪切力也较大；此时,折板膜组件对壁面剪切力的提升幅度也较大。
[Abstract]:Due to its advantages of low energy consumption, high pollution resistance and high water recovery rate, positive osmosis is a new water treatment technology in wastewater treatment. Seawater desalination and other fields have a wide application prospect, but the concentration polarization seriously reduces the filtration efficiency. In this paper, the folded plate structure is introduced into the design of orthoosmotic membrane assembly, aiming at the problem of external concentration polarization. In order to promote the generation and development of eddy current in the corridor and to reduce the heterodyne polarization, the corridor is wave-shaped along the flow direction. In this paper, the methods of experimental test and hydrodynamic calculation are used. The performance and mechanism of foldable membrane assembly were studied. The performance of folding plate membrane assembly was evaluated by comparing it with the traditional plate membrane assembly and taking the flat membrane assembly as the benchmark to evaluate the performance of the folded plate membrane assembly in reducing the polarization of the external concentration difference. The folding plate can slow down the polarization of the external concentration difference. The concrete manifestation is that the water flux. 2 M sodium chloride solution is the extraction solution. When deionized water is used as the raw material solution, the active layer moves towards the raw material solution and the active layer towards the extraction solution. The increase of water flux is 17.45% and 18.55.2 M sodium chloride solution is the extract solution and the corresponding value is 15.97% and 17.12, respectively, when the absorbent solution is 0.5 M sodium chloride solution as raw material solution, and the corresponding values are 15.97% and 17.12 respectively. The shape of the folded plate membrane has no significant adverse effect on the selectivity of the membrane. The shape of the foldable membrane module affects the increase of water flux, the larger waveform angle and the smaller wavelength, which are beneficial to the improvement of the water flux, while the Reynolds number affects the performance of the membrane module. When the Reynolds number is less than 800, the increase of water flux is larger, and when the Reynolds number is greater than 800, the increase of water flux decreases slightly with the increase of Reynolds number. The concentration of feedstock and extract affects the degree of concentration polarization, and when the Reynolds number is greater than 800, the increase of water flux increases slightly with the increase of Reynolds number. Furthermore, the performance of folding membrane module to slow down the polarization of external concentration difference is affected. When the concentration of absorbent liquid is higher or the concentration of raw liquid is lower, the water flux is larger. When membrane fouling and concentration polarization coexist, the membrane module can reduce membrane fouling. The flow characteristics in the monolateral corridor of the membrane assembly are analyzed by using the computational fluid dynamics software Fluent.The results show that the flow in the flat membrane assembly is relatively stable and there is no eddy current. The flow of fluid is completely along the x-axis: the laminated membrane assembly can promote the formation of eddy current in the corridor, and at the same time, the wall shear force is increased. The folding plate structure improves the hydraulic conditions by introducing eddy current. The flow characteristics in the corridor are affected by the shape of the foldable membrane module. When the wavelength is small and the waveform angle is larger, the eddy current in the corridor is stronger and the shear force on the wall is larger. Reynolds number will also affect the flow characteristics in the corridor. When the Reynolds number is larger, the eddy current is stronger and the wall shear force is larger in the laminate module, and in this case, the lifting range of the wall shear force of the foldable plate membrane assembly is also larger.
【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】：TQ028.8

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