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.
Concentration polarization is one of the main challenges of membrane-based processes such as power generation by reverse electrodialysis. Spacers in the compartments can enhance mass transfer by reducing concentration polarization. Active spacers increase the available membrane surface area, thus avoiding the shadow effect introduced by inactive spacers. Optimizing the spacer-filled channels is crucial for improving mass transfer while maintaining reasonable pressure losses. The main objective of this work was to develop a numerical model based upon the Navier–Stokes and Nernst–Planck equations in OpenFOAM, for detailed investigation of mass transfer efficiency and pressure drop. The model is utilized in different spacer-filled geometries for varying Reynolds numbers, spacer conductivity and fluid temperature. Triangular corrugations are found to be the optimum geometry, particularly at low flow velocities. Cylindrical corrugations are better at high flow velocities due to lower pressure drop. Enhanced mass transfer and lower pressure drop by elevating temperature is demonstrated.
The paper pertains to the analysis of the chemical interaction between sea water ions, asphaltene colloids and silicate /calcite mineral as a substrate during water/low salinity water flooding. The work tackles modeling of salinity dependent relative permeability and capillary pressure functions from contact angle to estimate oil recovery during water/low salinity water. The paper has two main parts. In the first part, static contact angle is calculated based on disjoining pressure and compared to the experimental values, reported in the literature. In the second part, the model is used to demonstrate that water film is more stable in presence of low salinity water compared to distilled water and sea water, for carbonate and silicate minerals. Increasing temperature enhances the stability of the water film around the substrate for both types of minerals. This could be future interpreted as an indication for extra oil recovery applying low salinity water injection at elevated temperature. It is interesting to observe from the model that, increasing the Mg 2+ ion concentration enhances the hydrophilicity characteristics for calcite mineral modified by asphaltene while for silicate surface modified by asphaltene, SO 4 2-ion enhances the hydrophobicity behaviour.
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