A Computational Study of Concentration Polarization in Novel Centrifugal Reverse Osmosis Module

Centrifugal reverse osmosis (CRO) is an emerging desalination method that promises significant energy efficiency over conventional reverse osmosis (RO) by introducing a spatially varying pressure field through module rotation, aligning more closely with the thermodynamic minimum energy requirements for separation. The presence of high-shear Ekman layers near the rotating membrane surfaces provides a strong motivation for mitigating concentration polarization. In conventional RO systems with spiral-wound membranes, the mass transfer coefficient (k) near the membrane—closely linked to concentration polarization—remains relatively uniform along the flow direction. In contrast, k varies significantly in centrifugal reverse osmosis (CRO) systems with disk membranes. As a result, the assumption of a constant k is invalid for CRO and necessitates the computation of the local mass transfer coefficient through CFD. This study investigates the impact of concentration polarization during CRO operation by one-way coupling the velocity and pressure fields—obtained using the asymptotic expansion method developed by Batista [Applied Mathematical Modelling 35 (2011) 5225–5233]—with the solute advection–diffusion equation in open-source software, OpenFOAM. The radial variation of the mass transfer coefficient will be evaluated for different feed flow rates and rotation speeds of a cylindrical CRO module operating with seawater (35 g/L), using a fixed module diameter of 0.5 m and a membrane permeability of 2 LMH/bar. Simulations across different rotational speeds will also determine the outlet pressure as a function of the module’s recovery rate, providing decision-makers with essential data to evaluate and compare the energy efficiency of the desalination system. By computing the local mass transfer coefficient for flow between rotating disks, this framework offers a physics-based approach to evaluating permeation through porous disks and optimizing operational parameters with concentration polarization effects explicitly accounted for.