New Insights into Computational Fluid Dynamic Modeling of the Resistivity and Overpotential in Reverse Electrodialysis

Abstract

The resulting electrical potential of a reverse electrodialysis is reduced both due to ohmic and non-ohmic resistances. The nonohmic resistance is mainly controlled by concentration polarization which is a considerable challenge in a membrane based processes and is a result of accumulation or depletion of specific ions adjacent to the ionic exchange membranes compared to the bulk solution. This phenomenon effectively reduces the driving force across the membrane, hence affects the performance of the process. The present work aims to present a numerical model based on coupled Navier-Stokes and Nernst-Planck equations to predict flow and pressure drop as well as concentration and electrical potential for optimizing the performance of the system, using OpenFOAM. The model is demonstrated in a flat and spacerfilled channel for different Reynolds number. The results reveal that reducing the Reynolds number and introducing flow promoters such as cylindrical corrugations in a dilute solution channel reduces the resistivity of a RED unit cell, hence increasing the produced electrical potential. However, introducing cylindrical corrugations in a concentrated solution channel has an adverse effect on the resistivity, leading to an unfavorable resistivity increment.

Electrodialytic Energy Storage System: Permselectivity, Stack Measurements and Life-Cycle Analysis

“…The cell resistance (mostly) increases with decreasing dilute concentration due to the decrease in the resistance of the dilute flow compartment. Jalili et al [46] simulated the resistance in the flow compartments in RED using OpenFOAM, where they found the resistance to be 0.4 mΩ m 2 and 0.04 mΩ m 2 for the dilute and concentrated solutions, respectively. These calculations are similar to our total calculated resistance.…”

Computational Fluid Dynamics Modeling of the Resistivity and Power Density in Reverse Electrodialysis: A Parametric Study

“…They observed that the spacer area fraction had a dominant effect only for less porous spacers [ 30 ]. Jalili et al [ 31 , 32 ] used CFD modeling to examine the influence of flow velocities and spacer topology with respect to the transport of mass and momentum, as well as the flow channel resistivity of a RED unit cell. They reported that the resistivity of the dilute solution channel dominates over the resistivity of the concentrated solution channel and membranes in a RED unit cell [ 32 ].…”

“…Similar observations have also been reported by Ortiz-Martinez et al [ 33 ]. The electrical potential of a RED unit cell was enhanced by reducing the flow velocity and introducing flow promoters in a dilute solution channel, due to reduced solution resistance [ 32 ]. Introducing spacers in a concentrated solution channel or increasing the flow velocity in a dilute solution channel increases the resistivity and has adverse effects on the electrical potential [ 32 ].…”

“…The electrical potential of a RED unit cell was enhanced by reducing the flow velocity and introducing flow promoters in a dilute solution channel, due to reduced solution resistance [ 32 ]. Introducing spacers in a concentrated solution channel or increasing the flow velocity in a dilute solution channel increases the resistivity and has adverse effects on the electrical potential [ 32 ]. They also demonstrated that the mass transfer is higher for active membrane-integrated spacers, compared to inactive spacers, under similar flow velocity and spacer topology, due to increased active membrane area [ 31 ].…”

“…We demonstrate that the electrical potential changes linearly with the height of the channel for a constant concentration profile, and that it follows a logarithmic trend with length of the channel height when the concentration profile varies linearly with the channel height [ 32 ]. Other interesting observations of this work [ 32 ] can be summarized as follows: First, the concentration gradient near the walls of the channel increase, due to reduced boundary layer thickness, with higher Re number. In fact, the concentration at the center of the channel is at its maximum for the concentrated solution channel and is at its minimum for the diluted solution channel [ 32 ].…”