Membrane plasma separation through small-area, hollow-fiber filters

The filtration capabilities of small polypropylene hollow-fiber plasma filters with membrane areas ranging from 100 to 1,000 cm2 have been investigated. It is found that the filtration flux per unit membrane area is approximately proportional to the wall shear rate gamma w at least up to gamma w = 7,500 s-1. As a result, the total filtration flow rate increases very little when the number of fibers is increased as the increase in membrane area is offset by the decrease in shear rate, but it increases with the fiber length L as L 2/3. Hemolysis occurs when the transmembrane pressure exceeds a certain threshold, but this threshold is itself an increasing function of shear rate. As a result, it is possible to circulate high blood flow rates even in very small filters (100 cm2) without hemolysis, provided the fiber length is below a critical value.