STRATIFIED MULTIPHASE MODEL FOR BLOOD-FLOW IN A VENULAR BIFURCATION

Available in vitro and in vivo experimental observations suggest that red cell aggregation and blood Vessel geometry are important determina nts of the flow characteristics of blood in Venules. However, no consi stent relationship has been observed between red blood cell aggregatio n and vascular resistance. The present work attempts to understand thi s relationship by evaluating computationally the effect of red cell ag gregation on the flow characteristics of blood in a converging vessel bifurcation. The proposed mathematical model considers blood as a two- phase continuum, with a central core region of concentrated red cell s uspension that is surrounded by a layer of plasma adjacent to the Vess el wall. In the central core region, blood is described by Quemada's n on-Newtonian rheological model, in which local Viscosity is a function of both the local hematocrit and a structural parameter that is relat ed to the size of red blood cell, aggregates. Fluids from the two feed ing branches are immiscible, which results in a stratified multiphase flow in the collecting venule. Calculations predict a complex, three-d imensional pattern of blood flow and generally nonaxisymmetric distrib ution of velocity, hematocrit, and shear stress in the collecting Venu le. The calculations are a first step toward a realistic model of bloo d flow in the venous microcirculation.