Department of Aeronautics & Astronautics, Stanford University, Stanford, CA, 94305, United States.
Department of Mechanical Engineering, Stanford University, Stanford, CA, 94305, United States.
Water Res. 2018 Sep 1;140:323-334. doi: 10.1016/j.watres.2018.04.042. Epub 2018 Apr 21.
Charge transfer and mass transport are two underlying mechanisms which are coupled in desalination dynamics using capacitive deionization (CDI). We developed simple reduced-order models based on a mixed reactor volume principle which capture the coupled dynamics of CDI operation using closed-form semi-analytical and analytical solutions. We use the models to identify and explore self-similarities in the dynamics among flow rate, current, and voltage for CDI cell operation including both charging and discharging cycles. The similarity approach identifies the specific combination of cell (e.g. capacitance, resistance) and operational parameters (e.g. flow rate, current) which determine a unique effluent dynamic response. We here demonstrate self-similarity using a conventional flow between CDI (fbCDI) architecture, and we hypothesize that our similarity approach has potential application to a wide range of designs. We performed an experimental study of these dynamics and used well-controlled experiments of CDI cell operation to validate and explore limits of the model. For experiments, we used a CDI cell with five electrode pairs and a standard flow between (electrodes) architecture. Guided by the model, we performed a series of experiments that demonstrate natural response of the CDI system. We also identify cell parameters and operation conditions which lead to self-similar dynamics under a constant current forcing function and perform a series of experiments by varying flowrate, currents, and voltage thresholds to demonstrate self-similarity. Based on this study, we hypothesize that the average differential electric double layer (EDL) efficiency (a measure of ion adsorption rate to EDL charging rate) is mainly dependent on user-defined voltage thresholds, whereas flow efficiency (measure of how well desalinated water is recovered from inside the cell) depends on cell volumes flowed during charging, which is determined by flowrate, current and voltage thresholds. Results of experiments strongly support this hypothesis. Results show that cycle efficiency and salt removal for a given flowrate and current are maximum when average EDL and flow efficiencies are approximately equal. We further explored a range of CC operations with varying flowrates, currents, and voltage thresholds using our similarity variables to highlight trade-offs among salt removal, energy, and throughput performance.
电荷转移和质量传输是电容去离子（CDI）脱盐动力学中的两个基本机制，它们是耦合在一起的。我们基于混合反应器体积原理开发了简单的降阶模型，该模型使用封闭形式的半解析和解析解来捕获 CDI 操作的耦合动力学。我们使用这些模型来识别和探索 CDI 单元操作（包括充电和放电循环）中流速、电流和电压之间的动力学中的自相似性。相似性方法确定了确定独特流出物动态响应的特定单元（例如电容、电阻）和操作参数（例如流速、电流）组合。我们在这里使用传统的 CDI 之间的流量（fbCDI）架构来演示自相似性，并且假设我们的相似性方法具有广泛应用于各种设计的潜力。我们对这些动力学进行了实验研究，并使用 CDI 单元操作的受控实验来验证和探索模型的限制。对于实验，我们使用了具有五个电极对和标准电极之间（电极）架构的 CDI 单元。在模型的指导下，我们进行了一系列实验，以展示 CDI 系统的自然响应。我们还确定了在恒流强制函数下导致自相似动力学的单元参数和操作条件，并通过改变流速、电流和电压阈值来进行一系列实验，以证明自相似性。基于这项研究，我们假设平均差分电双层（EDL）效率（衡量离子吸附速率与 EDL 充电速率之比）主要取决于用户定义的电压阈值，而流动效率（衡量从细胞内部回收脱盐水的效果）取决于充电期间流过的细胞体积，这由流速、电流和电压阈值决定。实验结果强烈支持这一假设。结果表明，在给定流速和电流下，当平均 EDL 和流动效率大致相等时，给定流速和电流的循环效率和盐去除率最大。我们使用相似变量进一步探索了具有不同流速、电流和电压阈值的 CC 操作范围，以突出盐去除、能量和吞吐量性能之间的权衡。
