Theory of solute dispersion in microfluidics: effect of assymetric velocity boundary layers

Contacts:

Henrik Bruus, DTU Nanotech, 4525-6399 (bruus@nanotech.dtu.dk)

Søren Vedel, DTU Nanotech, 4525-5742 (sove@nanotech.dtu.dk)

Web: http://www.nanotech.dtu.dk/microfluidics

(a) COMSOL simulation of concentration dispersion (color plot, red high concentration, blue low) in steady flow (arrows show velocity profile). (a1) t = 0, (a2) t = 0.05, (a3) t = 0.6. (b) Theoretically determined dispersion coefficient Deff as a function of time for steady flow (black line), and steady plus oscillating flow (thick gray line).

The use of fluids for transporting soluble matter is ubiquitous. Examples vary in both size and application: from large-scale industry such as breweries and ventilation, over the transport of nutrients in the vascular system to small-scale applications in microfluidics. Naturally, much research has been concerned with the dispersion of soluble matter in fluid flows, see Figure.

We have recently proposed a theory for solute dispersion (Vedel and Bruus, J. Fluid Mech., submitted 2010), which has opened up for new avenues of research. In this theoretical project you will follow one of these new ideas and investigate the effects of an asymmetric velocity field on solute dispersion. This question has practical importance in the field of electrokinetics (the motion of aqueous solution of ions), where asymmetric velocity fields are created experimentally in microchannels by external electric fields.

Following an introduction to the necessary hydrodynamics and electrodynamics, you will derive an analytical result for the asymmetric velocity field and study the dispersion. These theoretical predictions will be compared with numerical simulations you obtain with COMSOL, a general software for solving coupled, non-linear, partial differential equations. The goal of the project is to identify the changes in solute dispersion caused by the asymmetry of the velocity field and offer physical interpretations of these.