Importance of channel dimension for flow-electrode flowing in flow-electrode capacitive mixing (F-CapMix): Evaluation of net power density under high-pressure-drop conditions

Flow-electrode capacitive mixing (F-CapMix) utilizes ion adsorption/desorption on active materials in the flow electrode to harvest salinity gradient power. In order to facilitate flow-electrode flow in the F-CapMix unit cell, the current collectors should include a meandering flow channel for the cell assembly and should facilitate efficient electron transport between them and the flow-electrode active materials. This study evaluates the FCapMix performance variation and pumping power of the flow-electrode and feed water depending on flow channel depth. It was found that both parameters increased as the cross-sectional area of the flow channel narrowed. This result was due to the increasing linear velocity of the flow-electrode, which itself was associated with the narrowing cross-sectional area. The maximum gross power densities of the F-CapMix increased in a parabolic shape with respect to the flow-electrode linear velocity increase. (0.68 ->& nbsp;0.83 -> 0.86 -> 1.03 -> 1.14 W/m(2)) On the contrary, pumping power densities of the flow-electrode increased linearly (2.22 -> 2.98 -> 3.51 -> 5.93 -> 19.67 W/m(2)) with linear velocity increment of the flow-electrode. Further, the F-CapMix net power density was negatively affected by the increasing linear velocity of the flow-electrode (net power density variation from-2.06 to-19.10 W/m2), likely owing to the higher pumping power density required due to the narrower flow channel. This study verifies the importance of securing an appropriate cross-sectional area of the meandering flow channel to maintain positive net power of the F-CapMix.

Automated summary

This study evaluated the performance and pumping power of the Flow-electrode capacitive mixing (F-CapMix) system, and found that both the gross power density and pumping power density increased as the flow channel narrowed. However, the net power density decreased due to the higher pumping power required.