RESOLUTION DETERIORATION AND OPTIMAL OPERATING-CONDITIONS IN CENTRIFUGAL SPLITT FRACTIONATION .2. UNSTABLE DENSITY GRADIENTS

Resolution deterioration and optimal operating conditions are investig ated in a thin, rotating centrifugal SPLITT channel with unstable dens ity gradients. Flow mixing is believed to result from secondary flows which are induced by these unstable density gradients as they interact with inertial, viscous, and Coriolis forces in the channel. When pres ent, this mixing occurs between the feed and carrier substreams and si gnificantly disrupts nominal separation. The mixing onset boundary, wh ere separation resolution begins to degrade, is quantified where the f ractional loss in resolution is 10% of the resolution measured with st able density gradients in the channel. This boundary is compared to mi xing onset boundaries, based on similar criteria, for centrifugal SPLI TT channels with stable density gradients, and for gravitational SPLIT T channels with unstable density gradients. The onset of mixing in cen trifugal SPLITT channels with unstable density gradients shows complex dependence on the Reynolds number, Richardson number, Ekman number, R ossby number, and other flow parameters. (C) 1997 John Wiley & Sons, I nc.