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Introduction. Membrane capacitive deionization (MCDI) has the potential to become an energy efficient alternative to commonly used desalination technologies for slightly saline waters [1]. Energy consumption can further be optimized when selectivity for monovalent ions is enhanced and losses due to electric resistance are reduced. Thin, spacer filled flow channels promote electric conductivity within a desalination cell, but are challenging for flow simulations and tracer tests.
Experimental/methodology. Within the joint project innovatION, the development of a monovalent selective MCDI is supported by flow and process simulations using ANSYS [2]. Pressure loss experiments are used to calibrate and validate the flow model for 270 and 500 µm spacers and flow characteristics in lab- and pilot scale are determined with different tracers. The process model is implemented in ANSYS Fluent using User Defined Functions and is based on the modified Donnan approach [3]. Calibration data is obtained in lab scale, using different salt solutions at varying process paramters.
Results and discussion. By changing the inflow geometries, the pressure drop in laboratory scale could be reduced by 20 %. Tracer experiments showed that ink emerged as the most suitable tracer to visualize the flow profile and stagnation zones in thin flow channels. Furthermore, the results from the process model and the approach and challenges of modelling ion selectivity will be presented and discussed.

References
[1] Rosentreter, H.; Walther, M.; Lerch, A. Membranes 2021, 11, 126
[2] https://www.innovat-ion.de/en-US
[3] Biesheuvel, P.M. et al. Journal of Colloid and Interface Science 2011, 360, 239-248