微滤膜通道流场及强化传质研究

发布时间：2018-07-12 17:50

本文选题：微滤膜 + 强化传质　；参考：《西南石油大学》2017年硕士论文

【摘要】：膜分离技术因其过程无相变、无二次污染、分离效率高等优点而受到各国的普遍重视。然而,在膜分离过程中,物料中的微粒、胶体粒子或溶质大分子在膜上发生的吸附、孔堵、浓差极化和滤饼层的形成导致膜通量下降,分离效率降低,严重制约着膜技术的工业化进程。湍流促进器可以改善膜通道内的流体动力学条件,显著提高壁面流速或剪切速率,有助于抑制料液中的颗粒在膜表面的沉积,减轻微滤过程的膜污染现象,从而有效提高微滤膜通量。本论文使用湍流促进器强化错流微滤过程,通过CFD(Computational fluid dynamics)分析了平板膜通道内附加不同湍流促进器的流场,为湍流促进器的应用提供理论指导。首先,通过湍流促进器强化错流微滤过程,以速度场、压降以及壁面剪切应力为指标,研究了平行排布的湍流促进器结构形式、排布位置对强化传质效率的影响。研究表明,基于相同的湍流促进器形状及膜通道结构参数,排布于流道中部("浸没型")的湍流促进器能获得更高的壁面剪切应力,其中四棱柱湍流促进器能获得最高的压降和壁面剪切应力。发现湍流促进器诱发膜通道内流体形成旋涡,引起壁面流速波动,增大壁面剪切应力,显著提高流体的湍动强度,可以破坏边界层的发展,抑制料液中的颗粒在膜表面沉积,从而有效提高微滤膜通量。其次,针对四棱柱湍流促进器的结构特点,设计了一种新型的湍流促进器,CFD模拟膜通道内附加新型湍流促进器的流场,并考察湍流促进器结构参数,膜通道高度以及进口速度对流场特性的影响。流场分析表明,新型的湍流促进器能在获得较高壁面剪切应力的同时减小压降,即在强化传质效果较好的同时所需的能耗更小。最后,建立了附加温度场强化传质的湍流促进器模型,考察了不同进料水力攻角及进口速度的湍流促进器模型对微滤膜的强化传质及传热的影响。数值模拟结果表明:较高的进口流速有利于增大跨膜压差,壁面剪切应力以及温度极化系数τ,增大传质传热驱动力。进料攻角αf=45°的模型具备最优的传质传热效果,且所需能耗最小,当进口速度为0.14m/s时,传质通量达111.3Kg/m2h,是不含湍流促进器流道的15.7倍。分析了进料侧温度,颗粒质量流量以及颗粒粒径因素对膜通量的影响,对温度场强化传质的应用有重要的参考意义。
[Abstract]:Membrane separation technology has been paid more and more attention because of its advantages of no phase change, no secondary pollution and high separation efficiency. However, in the process of membrane separation, the adsorption of particles, colloidal particles or solute macromolecules on the membrane, pore blockage, concentration polarization and the formation of cake layer resulted in the decrease of membrane flux and separation efficiency. The industrialization process of membrane technology is seriously restricted. Turbulence promoters can improve the hydrodynamic conditions in the membrane channel, increase the wall flow rate or shear rate significantly, help to restrain the deposition of particles in the feed solution on the membrane surface, and reduce the membrane fouling phenomenon in the process of microfiltration. Thus, the flux of microfiltration membrane is increased effectively. In this paper, the cross-flow microfiltration process is enhanced by using turbulence promoters, and the flow field with different turbulence promoters in flat membrane channels is analyzed by CFD (Computational fluid dynamics), which provides theoretical guidance for the application of turbulence promoters. Firstly, the cross-flow microfiltration process was enhanced by the turbulence promoters. The effects of the parallel arrangement of the turbulence promoters on the mass transfer efficiency were studied by taking the velocity field, pressure drop and wall shear stress as the indexes. The results show that based on the same shape of turbulence promoters and structural parameters of membrane channels, turbulent promoters arranged in the middle of the channel ("immersion type") can obtain higher wall shear stress. The four-prism turbulence promoter can obtain the highest pressure drop and wall shear stress. It is found that turbulence accelerator induces vortex in membrane channel, causes wall velocity fluctuation, increases wall shear stress, increases turbulent intensity of fluid, destroys the development of boundary layer, and inhibits the deposition of particles on the membrane surface. Thus, the flux of microfiltration membrane is increased effectively. Secondly, according to the structural characteristics of the four-prism turbulence promoter, a new type of turbulence accelerator is designed to simulate the flow field in the CFD channel, and the structure parameters of the turbulence promoter are investigated. The influence of channel height and inlet velocity on the flow field characteristics. The flow field analysis shows that the new turbulence accelerator can obtain higher wall shear stress and reduce pressure drop, which means that the energy consumption is less when the mass transfer effect is better. Finally, a turbulence accelerator model with enhanced mass transfer with temperature field was established, and the effects of different hydraulic attack angles and inlet velocities on the enhanced mass transfer and heat transfer of microfiltration membrane were investigated. The numerical simulation results show that higher inlet velocity is beneficial to increase the pressure difference, wall shear stress and temperature polarization coefficient 蟿, and increase the driving force of mass transfer and heat transfer. The model with 45 掳angle of attack has the best heat transfer effect and the minimum energy consumption. When the inlet velocity is 0.14m/s, the mass transfer flux is 111.3 kg / m ~ 2 h, which is 15.7 times that of the flow channel without turbulence promoter. The effects of feed side temperature, particle mass flow rate and particle size on membrane flux were analyzed, which has important reference significance for the application of enhanced mass transfer in temperature field.
【学位授予单位】：西南石油大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O357.5

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