Geometry controlled dispersion in periodic corrugated channels

TL;DR

This paper develops a comprehensive approach to analyze the effective diffusivity of particles in periodically corrugated channels, covering narrow, wide, and intermediate regimes, and clarifies the physical mechanisms governing dispersion.

Contribution

It introduces a general method that includes narrow and wide channel limits, providing a Padé approximant scheme for dispersion analysis in various channel geometries.

Findings

Identifies all asymptotic scaling regimes of effective diffusivity.

Distinguishes between smooth and compartmentalized channels.

Links effective diffusivity to first passage problems in certain regimes.

Abstract

The effective diffusivity $D_e$ of tracer particles diffusing in periodically corrugated axisymmetric two and three dimensional channels is studied. The majority of previous studies of this class of problems are based on perturbative analyses about narrow channels, where the problem can be reduced to an effectively one dimensional one. Here we show how to analyze this class of problems using a much more general approach which even includes the limit of infinitely wide channels. Using the narrow and wide channel asymptotics, we provide a Pad{\'e} approximant scheme that is able to describe the dispersion properties of a wide class of channels. Furthermore, we systematically identify all the exact asymptotic scaling regimes of $D_e$ and the accompanying physical mechanisms that control dispersion, clarifying the distinction between smooth channels and compartmentalized ones, and identifying the regimes in which $D_e$ can be linked to first passage problems.