The influence of flow electrode channel design on flow capacitive deionization performance: Experimental and CFD modelling insights

Flow capacitive deionization (FCDI) is an emerging desalination technology at which flow electrodes (shear-thinning flowable carbon slurries) are used to remove ions from saline water. The geometry of flow electrode channels, which provide the path and ensure the distribution and mixing of the flow electrodes, is one of the most important aspects to be optimized. This work presents experimental and computational fluid dynamics (CFD) modelling analysis of the influence of the geometry of flow electrode channels on FCDI performance. Flow electrode gaskets (with open, serpentine (short) horizontal and serpentine (long) vertical channels) were 3D printed using a polyethylene terephthalate glycol (PET-G) filament. The FCDI cell with a vertical serpentine flow electrode channel exhibited the poorest performance due to channel blockage by carbon particles, while the best results were achieved with a horizontal serpentine flow electrode channel. CFD simulations aided in understanding this behaviour by showing that the channel geometry strongly affects the local shear rate, and thus the local viscosity of flow electrodes. Thus, it is recommended to design channels that induce flow disturbance aiming for increasing the shear rate and hence reducing flow electrode viscosity, therefore promoting their flowability and reducing clogging chances.