Numerical study of concentration polarization of reverse osmosis film via the lattice Boltzmann method

Abstract

The concentration polarization is the main factor affecting the water production rate of reverse osmosis. This article proposes a new numerical model based on the lattice Boltzmann method for simulating concentration polarization that can easily handle the computational instability caused by small diffusion coefficient. Based on this model, the concentration polarization in empty channel and unilateral spacer channel are simulated, respectively. The results show that the thickness of the CPL is generally about one tenth of the channel height. Increasing the Re can weaken concentration polarization, reduce the thickness of the CPL, and thereby increase permeate flux. Increasing the TMP can increase permeation flux, but it also accelerates the accumulation of solute increases the solute concentration within the CPL, and accelerates fouling. The spacer can effectively weaken the concentration polarization and increase permeate flux. But the unilateral spacer can cause uneven performance of the upper and bottom membranes.