Membrane distillation (MD) is driven by vapor pressures rather than hydraulic pressures. Consequently, certain regions of the membrane may be in an unrestrained state, which potentially lead to membrane vibrations due to the turbulence caused by crossflow. However, this crossflow-induced membrane vibration has been largely overlooked in the previous studies. Here, we made the first attempt to investigate the crossflow-induced membrane vibration through the observation using optical coherence tomography (OCT), and explore the effect of this vibration on membrane fouling and scaling. The experimental results revealed that the vibration exhibited a self-excited vibration mode, with amplitudes reaching tens of micrometers. Moreover, the amplitude could be readily adjusted through changing crossflow velocity, transmembrane pressure, and the mesh size of spacer. For humic acid (HA) fouling, the membrane vibration could effectively reduce the thickness of HA cake layer, thereby stabilizing the specific flux at a constant level of 0.85, in contrast to the continuous decline of the flux under non-vibration condition. For gypsum scaling, the membrane vibration allowed the MD under low crossflow velocity (5 cm/s) to achieve comparable scaling occurrence concentration and scaling layer thickness as those under high crossflow velocity (10 cm/s). Our findings emphasized the potential of crossflow-induced membrane vibration as an effective strategy to mitigate membrane fouling and scaling in MD and other non-pressure driven membrane systems.
As a factor affecting the efficiency of hollow fiber membrane filtration, air resistance is gradually being discovered. To obtain a better air resistance control strategy, in the study, two representative strategies have been proposed, namely, membrane vibration and inner surface modification, which was achieved by aeration combined with looseness-induced membrane vibration and dopamine (PDA) hydrophilic modification of the inner surface, respectively. The performance of two strategies was based on Fiber Bragg Grating (FBG) sensing technology and ultrasonic phased array (UPA) technology to achieve real-time monitoring. Mathematical model result shows that in hollow fiber membrane modules, the initial appearance of air resistance causes a rapid reduction in filtration efficiency, while this effect diminishes as the air resistance increases. Besides, experimental results show that aeration combined with fiber looseness helps to inhibit air aggregation and accelerate air escape, while inner surface modification enhances the hydrophilicity of inner surface, weakens the air adhesion and increases the drag force of fluid on air bubbles. In the corresponding optimized state, both strategies perform well in optimizing the air resistance control, and the improvement in flux enhancement ability for the two strategies is 26.92 and 34.10%, respectively.
危险品化学品经营许可证（带存储）