Abstract Forward osmosis-based processes are low energy separation technology that can help in the recovery of fresh water. The design of such systems is approximated either from the simple mass conservations or using the analogy of heat exchanger design correlations. Such relationship has serious drawbacks, particularly at high recoveries, when the impact of mass transfer boundary layer is paramount. Unlike the reverse osmosis, the permeate flux (hence the recovery) is reduced with the convection (Peclet number, Pe). The membrane surface concentration and the thickness of concentration boundary layer on the draw side decreases with Pe. Since, permeate flux increases with the surface concentration, the recovery is dependent on Pe. Besides the relative concentration and flow-rates, the membrane area is influenced by the mass transfer boundary layer, manifested through Pe. The results reported in the Mondal and Field (2018) is a special case when Pe ≪ 1 (negligible convection), leading to maximum recovery. We evaluate the required membrane area and the performance of the forward-osmosis system as a function of the operating conditions, including the Pe. We have identified the range of operating conditions, for which the sizing of FO system is underpredicted in the case of negligible convection and the log-mean concentration difference.

中文翻译：

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基于详细传质边界层分析的正向渗透质量交换器的性能

摘要 基于正向渗透的工艺是一种低能耗的分离技术，可以帮助回收淡水。此类系统的设计近似于简单的质量守恒或使用热交换器设计相关性的类比。这种关系具有严重的缺点，特别是在高回收率时，当传质边界层的影响至关重要时。与反渗透不同，渗透通量（因此回收率）随着对流（佩克莱数，Pe）而降低。引出侧的膜表面浓度和浓度边界层厚度随 Pe 的增加而减小。由于渗透通量随着表面浓度的增加而增加，因此回收率取决于 Pe。除了相对浓度和流速外，膜面积还受传质边界层的影响，通过Pe表现出来。Mondal and Field (2018) 报告的结果是 Pe ≪ 1（对流可忽略不计）时的特殊情况，导致最大恢复。我们根据操作条件（包括 Pe）评估所需的膜面积和正向渗透系统的性能。我们已经确定了操作条件的范围，在对流和对数平均浓度差异可忽略不计的情况下，FO 系统的大小预测不足。