Abstract Calcium sulfate (CaSO4) scaling is a limiting factor in membrane distillation as a result of concentration polarization and elevated temperatures. We assessed the influence of radio-frequency magnetic fields, used as a method of heating the membrane's surface, as part of a membrane distillation (RF-MD) process. The influence of RF heating on CaSO4 scaling is addressed in terms of distillate flux and crystal formation, and the results are compared to conventional MD systems. The RF-MD system included a thermally conducting dual-layer membrane containing a magnetic hydrophilic layer based on iron oxide-carbon nanotubes coated on a hydrophobic membrane. Heating the solution was mainly done directly at the membrane-water interface, and scaling was assessed at different feed flow velocities using feed solutions containing elevated concentrations of CaSO4 and NaCl and at ionic composition simulating RO brine. Results show only sporadic small CaSO4 crystals on the membrane surface following RF-MD, while high concentrations of small crystals were detected at the concentrate stream exiting the filtration module. Furthermore, the RF-MD system was able to produce enhanced distillate flux. The scaling mitigation mechanism is discussed in detail and hypothesized to be a result of the high-frequency movement and collision of the ions in the solution.

中文翻译：

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射频感应加热膜蒸馏中的结垢缓解

摘要 由于浓差极化和温度升高，硫酸钙 (CaSO4) 结垢是膜蒸馏中的一个限制因素。我们评估了射频磁场的影响，该磁场用作加热膜表面的方法，作为膜蒸馏 (RF-MD) 过程的一部分。RF 加热对 CaSO4 结垢的影响在馏出物通量和晶体形成方面得到解决，并将结果与​​传统的 MD 系统进行比较。RF-MD 系统包括一个导热双层膜，其中包含一个基于氧化铁-碳纳米管的磁性亲水层，该层涂覆在疏水膜上。加热溶液主要直接在膜-水界面进行，使用含有高浓度 CaSO4 和 NaCl 的进料溶液以及模拟 RO 盐水的离子组成，在不同进料流速下评估结垢。结果表明，RF-MD 后膜表面上只有零星的小 CaSO4 晶体，而在离开过滤模块的浓缩液流中检测到高浓度的小晶体。此外，RF-MD 系统能够产生增强的馏出物通量。详细讨论了结垢缓解机制，并假设是溶液中离子高频运动和碰撞的结果。而在离开过滤模块的浓缩液流中检测到高浓度的小晶体。此外，RF-MD 系统能够产生增强的馏出物通量。详细讨论了结垢缓解机制，并假设是溶液中离子高频运动和碰撞的结果。而在离开过滤模块的浓缩液流中检测到高浓度的小晶体。此外，RF-MD 系统能够产生增强的馏出物通量。详细讨论了结垢缓解机制，并假设是溶液中离子高频运动和碰撞的结果。