Residence time distributions for in-line chaotic mixers.

We investigate the distributions of residence time for in-line chaotic mixers; in particular, we consider the Kenics, the F-mixer, and the multilevel laminating mixer and also a synthetic model that mimics their behavior and allows exact mathematical calculations. We show that whatever the number of elements of mixer involved, the distribution possesses a t^{-3} tail, so that its shape is always far from Gaussian. This t^{-3} tail also invalidates the use of second-order moment and variance.