Behavior of model particles and blood cells at spherical obstructions in tube flow

Abstract

The effects of vessel obstructions on circulating blood cells were modeled using dilute suspensions of microspheres, red cells and platelets flowing past spherical obstructions in 0.79–1.27-mm glass tubes. Rapid acceleration of the fluid at the obstruction resulted in a large increase in wall shear rate up to 5000 sec −1. Subsequent sudden deceleration distal to the sphere led to separation of fluid from the wall with reverse flow and formation of a vortex in which particles described spiral orbits. In the reverse flow zone, wall shear rates were only 1.5–9% of those in flow far away from the obstacle. Particles spent from 10 to 10 3 times as long in orbits as the time taken to traverse the vortex length at the mean tube flow rate. The size of the vortices traced out by microspheres of different diameters, red cells and platelets, were identical in a given tube but due to radial migration away from the wall, the larger particles entered the vortex further from the surface of the spherical obstruction than the smaller particles, whose relative vortex concentration thereby increased. Two-micrometer latex spheres dispersed in plasma, which formed aggregates during flow, were also observed and found to adhere to the downstream edge of the obstruction near the tube wall, but not elsewhere in the vortex or in the tube.