基于污染物临界粘附力的超滤动态过程的CFD模拟

针对膜污染的动态变化问题,通过计算流体力学(CFD)手段建立了中空纤维膜的二维轴对称模型,综合考虑了污染物间粘附力及水流剪切力的影响,提出有效剪切应力的概念,在模型中耦合了变形几何、自由多孔介质流动及稀物质传递3种物理场,将污染物法向积累、切向有效剪切与污染物界面处的网格速度相关联,建立了膜面污染物截留的动态模型.依据死端过滤与错流过滤的实验数据,确定出模型的匹配参数.在此基础上,研究了不同进给方式(连续流与脉冲流)对膜面污染物的影响.模拟结果表明,当水流剪切力足以克服污染物的临界粘附力时,可对膜面污染物起冲刷作用;与连续流相比,脉冲流具有更高的有效剪切速率,在对膜面污染物的冲刷作用方面更具优势.

CFD simulation of the dynamic ultrafiltration process based on the foulant critical adhesion force

In this study, a two-dimensional(2D) axisymmetric model for hollow fiber membrane was developed by using computational fluid dynamics (CFD) simulation, aiming at describing dynamic variation of UF membrane fouling.Considering the influence of foulant-foulant critical adhesion force and shear force, the concept of effective shear force was put forward.The model was also coupled with deformed geometry, free and porous media flow, the transport of diluted species.Grid velocity at the pollutant interface was related to the normal accumulation of foulants and the tangential shear.The fitting parameters of the model were determined by dead-end and cross-flow filtration experiments.Based on this model, the influece of feed modes (continuous flow and pulsatile flow) on membrane fouling was investigated.The results show that foulants would be scoured when the shear force of flow was stronger than the given critical adhesion force.Compared with continuous flow, pulsatile flow could provide a higher effective shear rate and is beneficial to scouring foulant on the membrane surface.