Thermodynamic effects are of great importance in both systems.
We are engaged in an intensive experimental effort in measuring permeation rate and solute rejection in various membrane ultrafiltration units, e.g. stirred cells and later tubular membranes. Both cells and tubular membranes were specially adapted so that different permeate collection areas were created, thus enabling the study of the effect of local mass-transfer coefficients. Transmembrane pressure, feed concentrations and stirrer speed or circulation velocity were used as operating variables. Hand in hand with the experimental work the theoretical framework was taken up. In our modelling of the transport inside the membrane we worked out the existing literature models, on one hand the hydrodynamic models with idealised particle motion, on the other hand the continuum models of the Maxwell-Stefan type.