Analysis of ultrafiltration processes with dilatant macromolecular solutions by means of dimensionless numbers and hydrodynamic parameters

Fouling in ultrafiltration was modelled in terms of dimensionless correlations and the Sherwood number using a polyethylene glycol aqueous solution. The rheological nature of this solution was dilatant. Tubular ceramic membranes of 35 kDa molecular weight cut-off were used in the experiments that were performed in turbulent flow conditions. Steady-state fluxes were correlated with several hydrodynamic parameters: Sherwood number, transmembrane pressure, shear rate, shear stress, Reynolds number and crossflow velocity. Power-law fittings were used to analyze experimental data and high correlation coefficients were obtained. Dimensionless correlations showed a similar synergy between membrane and polyethylene glycol solutions and they revealed the formation of a concentration polarization layer and the existence of a critical crossflow velocity among which no polarization phenomena (concentration polarization layer and cake layer) was observed. The results confirmed that rheological properties had less influence on the shear rate than in the case of the shear stress.

Research highlights▶ There was a critical crossflow velocity among which no polarization phenomena existed. ▶ The concentration polarization and the cake layers can be removed at high CFVs. ▶ Excellent fittings were obtained for the dimensionless analysis performed. ▶ Model coefficients were found to depend on operating conditions. ▶ Rheological properties have less influence on shear rate than on the shear stress.