The effective diffusivity for a passive impurity in a steady convecting flow is calculated in the experimentally relevant limit of large Péclet number (p=vl/D). The expulsion of the concentration gradients from the region of closed stream lines leads to the enhancement of the diffusivity D by a factor of $p^{1/2}$.

• Received 27 January 1987

DOI:https://doi.org/10.1103/PhysRevA.36.261