Abstract: Numerical calculations were conducted to simulate the flow and mass transfer in narrow membrane channels with and without flow disturbers. The channel consists of an impermeable solid wall and a membrane surface with a spacing of 2.0mm. The flow disturbers studied include rectangular winglets, which are often used as longitudinal vortex generators to enhance heat transfer in heat exchanger applications, as well as square prism, triangular prism, and circular cylinder, which are used here to mimic the traditional spacer filaments for comparison of their abilities in enhancing the convective mass transfer near the membrane surface to alleviate the concentration polarization. The disturber performance was evaluated in terms of concentration polarization factor versus consumed pumping power, with a larger factor meaning a more serious concentration polarization. Calculations were carried out for NaCl solution flow with Reynolds numbers ranging from 400 to 1000. The results show that the traditional flow disturbers can considerably reduce the concentration polarization but cause a substantial pressure drop, while the rectangular winglets can effectively reduce the concentration polarization with a much less pressure drop penalty. The rectangular winglets were optimized in geometry under equal pumping power condition.

Key words: Membrane, Concentration polarization, Mass transfer enhancement, Rectangular winglet, Pumping power

摘要： Numerical calculations were conducted to simulate the flow and mass transfer in narrow membrane channels with and without flow disturbers. The channel consists of an impermeable solid wall and a membrane surface with a spacing of 2.0mm. The flow disturbers studied include rectangular winglets, which are often used as longitudinal vortex generators to enhance heat transfer in heat exchanger applications, as well as square prism, triangular prism, and circular cylinder, which are used here to mimic the traditional spacer filaments for comparison of their abilities in enhancing the convective mass transfer near the membrane surface to alleviate the concentration polarization. The disturber performance was evaluated in terms of concentration polarization factor versus consumed pumping power, with a larger factor meaning a more serious concentration polarization. Calculations were carried out for NaCl solution flow with Reynolds numbers ranging from 400 to 1000. The results show that the traditional flow disturbers can considerably reduce the concentration polarization but cause a substantial pressure drop, while the rectangular winglets can effectively reduce the concentration polarization with a much less pressure drop penalty. The rectangular winglets were optimized in geometry under equal pumping power condition.

关键词: Membrane, Concentration polarization, Mass transfer enhancement, Rectangular winglet, Pumping power