  Thrombosis is a common complication following the surgical implantation of
blood contacting devices, and is strongly influenced by the phenomenon of
near-wall enrichment of platelets. This paper describes a multi-constituent
continuum approach to study this phenomenon. A mixture-theory model is used to
describe the motion of the plasma and the red blood cells (RBCs) and the
interactions between the two components. A transport model is developed to
study the influence of the RBC field on the platelets. The model is used to
study blood flow in a rectangular micro-channel, a sudden expansion
micro-channel, and a channel containing micro crevices (representing a
practical problem encountered in most blood-wetted devices). The simulations
show that in the rectangular channel the concentration of platelets near the
walls is about five times higher than the concentration near the centerline of
the channel. It is also noticed that in the channel with crevices, extremely a
large number of platelets accumulate in the deep part of the crevices and this
may serve as the nidus for thrombosis occurring in medical devices.
  Keywords: Platelets; Blood flow; RBCs; Micro-channel; Mixture theory;
Two-fluids; Thrombosis
