A comparative study between stirred dead end and circular flow in microfiltration of China clay suspensions

A well-defined comparative study between stirred dead end and circular crossflow for microfiltration of china clay suspensions has been undertaken. The comparisons have been made with respect to convective mass transfer coefficients, permeation and rejection rates, and energy consumption. Similar operating and hydrodynamic conditions were implemented for the comparison. According to our experimental data the circular crossflow module was proven to perform better as compared with the stirred dead end system due to the higher mass transfer coefficients, higher permeation rates and lower energy consumption. The mass transfer coefficients observed are comparable to those previously found in vortex flow filtration and dead end flow filtration. The presence of Dean vortices in the circular crossflow module promotes flow instabilities in the curved channel flow path which reduce the concentration polarization effect during the filtration process. The concentration polarization effect however deteriorated due to solute build up (high solute concentration at the membrane surface) and decrease of the shear stress, i.e., the particle lift forces on the membrane surface. This resulted in deposition of particles on the membrane surface. In terms of energy consumption, for the same energy cost the limiting flux reached in circular crossflow was found to be higher than in the stirred dead end unit.