Observed sieving coefficient

Due to concentration polarization, the solute concentration near the membrane surface tends to be higher than that in the bulk feed. Another sieving coefficient term that is commonly used is the apparent or observed sieving coefficient (S ) which is defined as... 

Correspondingly, the observed solute transmission or sieving coefficient. Sobs, will be different from the trae value, Sa e, where... 

The two-phase systems of interest here are SCF-liquid and SCF-solid. Lahiere et al. (1987) have studied the transfer of ethanol or propanol from an aqueous solution into supercritical CO2. The experimental extraction behavior in a sieve-tray extractor was compared with that predicted from a model used for common liquids. This model for subcrit-ical liquids uses overall mass-transfer coefficients obtained from the individual film coefficients by the conventional sum of the two resistances approach. Lahiere et al. (1987) observed reasonable correspondence between experimentally observed values and the performance predicted from conventional models. For SCF-solid systems with pure solids, Debenedetti and Reid (1986) have observed that the mass-transfer coefficient for the SCF phctse is very strongly influenced by natural convection. This happens because the SCF has very low viscosity and yet has a high density, leading to a much more important role of natural convection than in normal liquids. 

---