Modeling of external and internal concentration polarization effect on flux behaviour of forward osmosis

The forward osmosis process has recently gained more interest from researchers and is being viewed as an alternative to various membrane processes. The primary challenge in developing the process is the severity of both external and internal concentration polarizations, which significantly reduce the water flux across the highly selective membrane. This study investigates the impact of concentration polarization on flux behaviour. A model adopted from the boundary layer concept was used to describe the external concentration polarization effect. A previously developed model for the internal concentration polarization was further improved from the governing convective-diffusion equations, to achieve a better transport model that was in excellent agreement with experimental flux data. Laboratory experiments were carried out to account for both the external and internal concentration polarization and the associated water flux was verified with the improved models. Results showed excellent agreement for both models, which were used to describe external and internal concentration polarization, and these modified models were more accurate than previously used models.