Optimal Control Of Membrane Processes Based On In Situ Monitoring Of Structural Flow Fields In Hollow Fiber Membranes

As an important part of membrane separation process,hollow fiber membranes have been widely used due to their long lifetimes,low cost and excellent filtration performance.However,membrane fouling,a major factor hindering the development of membrane technology,has led to the degradation of membrane module performance and energy wastage.The flow field,an important means of membrane fouling control,is more complex due to the structural characteristics of hollow fiber membranes.Therefore,in this paper,we divided the flow field into external and internal flow fields according to the structural characteristics of hollow fiber membranes,and optimised them separately.The main research contents and conclusions covered are as follows:In the external flow field of hollow fiber membranes,based on the Fiber Bragg Grating(FBG)sensing technology,which is similar to the scale of hollow fibers,we investigate the effect of intermittent pulse variations of the fluid in single-phase flow mode on membrane fouling control.The results show that the instantaneous turbulence effect of pulses can effectively mitigate membrane fouling,as shown by the choice of a pulse mode with high pulse frequency and low fluid velocity,which is conducive to the enhancement of turbulence and shear effect.The effect of membrane fouling control is significant.Secondly,we investigate the shear characteristics of the membrane surface in the external flow field of hollow fiber packing density under gas-liquid two-phase flow,and achieves an in-situ analysis of the flow field in the membrane system with the help of FBG technology.The results show that increasing the aeration strength and appropriate fiber packing density facilitates the distribution of shear forces in the axial direction of the fibers,enhancing the tangential shear effect and improve the effectiveness of membrane fouling control.Furthermore,investigates the influence of the hollow fiber membrane module feed structure,crossflow and aeration on the key factors of shear force and fiber tensile strength in the external flow field.The results showed that crossflow with low aeration intensity has a significant contribution to shear force in the membrane module.Increasing tangential shear and reducing excessive localised shear will help to reduce the damage it causes to the fibers.Monitoring and optimisation of the flow field shear will help to maximise its functionality.In addition,for the internal flow field of hollow fiber membranes,based on ultrasonic phased array(UPA),we first investigated the air resistance caused by the released air in the inner lumen of the membrane and proposes an optimisation strategy for the inner flow field of the hollow fiber membrane.The results show that there is a positive correlation between air resistance,TMP and the amount of air released.By promoting the air dispersion and redissolution can effectively reduce air resistance in the backwash process.Besides,the formation of " air resistance" in the internal flow field of hollow fiber membranes is combined with the aeration-enhanced membrane vibration and the dopamine(PDA)hydrophilic modification of the inner surface,and the ability of the two strategies to control air resistance is compared.The results show that both strategies have good air resistance control and flux enhancement effects,specifically,the aeration-induced membrane vibration promotes the timely discharge of air in the form of tiny bubbles,and the hydrophilic modification reduces the adhesion of air.