REPRESENTATIONS OF COUPLING IN OSMOTIC MEMBRANES

The flow coupling phenomena that occur in non-ideal semipermeable membranes can be described in several ways. In particular, some recent literature has treated the solute and solvent flows directly, while other literature has treated solute and total volumetric flows. In many cases of practical interest, the solute flow is sufficiently small so that solvent flow expressed in volumetric terms and total volumetric flow are essentially equal. However, even when this is the case, the coupling coefficients calculated using the two different flow representations have quite different meanings. Two recent calculations of coupling coefficients using a frictional membrane model have yielded two different results. These results are consistent with one another; they differ because one is the coupling coefficient in the solute flow-solvent flow representation, while the other is the coupling coefficient in the solute flow-total flow representation. © 1969.