On solute dispersion by electroosmotic flow through a rectangular micro-channel subject to wall absorption

This paper investigates the all-time development of hydrodynamic solute dispersion in a two-dimensional electroosmotic flow through a three-dimensional rectangular microchannel with walls that absorb solute at a constant rate. The solute transport problem is solved by extending the generalized dispersion approach to a three-dimensional electroosmotic flow system. Furthermore, the moment-based method is scaled up to systematically determine the time-dependent transport coefficients. The overall transport behavior is characterized using various transport coefficients, together with the solute concentration distribution at selected times. The effect of the channel aspect ratio on solute dispersion is quantified under reactive boundary conditions. The findings show that wall absorption is a major cause of solute mass loss and suppresses the asymmetry of the solute concentration distribution, although its effect on asymmetry remains relatively weak at early times. It is further shown that channel geometry and electric double-layer thickness significantly influence velocity nonuniformity, thereby modulate longitudinal spreading. The theoretical predictions are validated against Brownian dynamics simulations, which show excellent agreement with the calculated concentration moments and distribution profiles.