Assessing the Impact of Concentration-Dependent Fluid Properties on Concentration Polarization in Crossflow Membrane Systems

Abstract

The effects of concentration-dependent fluid properties (viscosity, diffusivity, and osmotic-pressure coefficient) of sucrose−water solution on the permeate flux, wall concentration, Sherwood numbers, and velocity profiles in three different membrane systems were assessed using a 2D finite element model, which was developed by modifying the fluid property terms to incorporate the concentration dependency in a coupled concentration polarization model that was developed earlier. It was found that wall concentration, permeate velocity, and Sherwood numbers were significantly affected by the variations of the fluid properties. If any of the concentration dependencies of the fluid properties is neglected, wall concentrations would be either significantly overestimated or underestimated, whereas permeate velocity would always be overestimated. In different membrane systems, the relative importance of the effects of the concentration-dependent viscosity, diffusivity, and osmotic-pressure coefficient on wall concentration and permeate velocity may vary. These results suggest that the effects of concentration-dependent properties on concentration polarization would be strongly affected by the system operating conditions, especially the system value of Δp/Δπ0. It was also found that the errors in the solution of Berman for the velocity profile may be considerable when the variations of the fluid properties are considered under the simulation conditions.