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Particles sedimenting in a viscoelastic fluid form chains. It has been observed in experiments that, sometimes, the last particle in the chain gets detached. In this paper, we investigate this phenomenon. It is known that a long chain falls faster than a single particle in fluids. This long body effect tends to detach the last particle from the chain. The wake effect and the normal stress effect are the mechanisms that work against the long body effect. The last particle is not detached if the inertial wake effects are strong enough to cause substantial drag reduction on it. The detachment is also restricted by the elastic normal stress of the viscoelastic fluid.

In this note we present a proof showing that the contribution from the extra stress tensor to the normal component of the stress on the surface of a moving rigid body in an incompressible Oldroyd-B fluid is zero. [DOI: 10.1115/1.1436095]