Physical similarity and parametric sensitivity analysis of the capacitive deionization process

Capacitive deionization is an electrochemical ion removal technique that has broad application prospects for the efficient desalination of brackish water. The current research mainly focuses on the improvement of the electrode material performance and device structure for capacitive deionization. However, the capacitive deionization process is subject to the coupling effect of multiple physical parameters inside the porous electrode, the dominant order and optimization of multiple physical parameters in the capacitive deionization process are needed to be further investigated. In this study, the ion transport in porous electrode of the capacitive deionization is investigated via numerical simulation and physical similarity analysis. Fourteen dimensional physical parameters involved in ion transport are unified into eight dimensionless parameters based on the nondimensionalization of Navier–Stokes and Poisson–Nernst–Planck equations, and the dimensionless parameters are summarized into four categories, including ion adsorption capability, ion transport characteristics, ion motion driving force, and ion adsorption equilibrium time. Analysis based on the numerical models with an irregular porous electrode structure shows that the dimensionless parameters can explain a series of similar physical phenomena in the capacitive deionization processes. Moreover, a parametric sensibility analysis is performed to reveal that the concentration and velocity of inlet solution are dominant factors for optimizing the salt adsorption capacity per unit area and the average salt removal rate. In addition, the inlet solution concentration and electrode potential are critical factors for improving the removal efficiency. The physical similarity and parametric sensitivity analysis in this study provide theoretical guidance for performance improvement in the practical application of capacitive deionization.