Figure 13.

The translational diffusion coefficient of neutrally buoyant Brownian particles of different radii a initially placed at different locations h from the wall of the circular tube in Poiseuille flow, in the diffusive regime ${\tau }_b\ll t\ll 1∕\stackrel{·}{\gamma }$. Solid and dashed lines correspond to the perturbation solutions given in Happel and Brenner (Ref. ⁵⁵) and Goldman et al. (Ref. ⁶⁰).