(227ab) Bifurcation Flows of Suspensions: Flow Splits and Mixture Boundary Conditions

The flow of neutrally buoyant suspensions in bifurcating channels will be described based on an experimental study in millimeter-scale square cross-section channels.  Bifurcations of an asymmetric T and a Y geometry are discussed.  The flow behavior of a pure Newtonian liquid and suspensions of solid volume fraction varying from 5-45% are studied for bulk Reynolds numbers of O(10)-O((1000).  The suspension flow is found to differ strongly from the pure fluid flow in the asymmetric T, and this is found to be related to particle migration upon approach to the bifurcation.  A method for predicting the features of this behavior based on straight channel suspension flow simulations (made using lattice-Boltzmann calculations) and pure liquid flow in the T geometry is presented. Observations include strong separation in the T geometry, with particle depletion in the separated zone, and in both T and Y geometry, particle collision with the boundary at Re = O(100) for particles of 1/10 the channel width. These observations motivate a consideration of the appropriate form for the boundary condition for each of the two phases and continuum calculations of the mixture flows are presented to illustrate the effects of these conditions.