Rotational Motion of Large Particulate Doublets in Poiseuille Flow in a Capillary

Doublets of 48-μm-diameter polystyrene latex particles are experimentally tracked in a Poiseuille flow in a capillary tube. The rotational motion of nine doublets is observed using video microscopy with a translating stage. The particle diameter to capillary diameter ratio is 0.17, volume concentration 0.5%, and Reynolds number approximately 0.5. The rotational motions of the “large” particulate doublets are compared with theory originally developed for doublets with particle-to-tube diameters of the order of 0.04; the doublet rotations in the present experiments agree reasonably well with the earlier theory when the shear rate for the large doublet is defined based on the location of the centroid of shear rather than the shear rate at the radial center of mass of the rotating doublet. Additionally, these doublets are readily classified as primary or secondary on the basis of the rotational period.