Numerical study on ion transport and electro-convective mixing of power-law fluid in a heterogeneous micro-constrained channel

Mixing performance with variable solubility in a modulated micro-channel filled with non-Newtonian power-law fluid is studied. A combined geometrical and surface potential heterogeneity of one wall of the channel is considered to promote mixing of eluted species with electrolytes. The stability and energy budget analysis are made to check the flow distortion due to the presence of heterogeneity in channel geometry as well as surface charge density. The analytical solutions for the electric potential and velocity are obtained for different types of electrolytes through the Debye-Huckel approximation. The Poisson-Nernst-Planck-Navier-Stokes equations are computed to evaluate the electroosmotic flow due to the non-Newtonian fluid, charge distributions, and species concentrations. Convective flow induced by the patterned surface is taken into account to achieve an efficient mixing of two different streams of fluid injected in the channel. The combined effect of in-build pressure gradient and external electric field drives the species transport in the modulate channel. Comparisons of species mixing efficiency and pressure drop are made for different forms of the surface heterogeneity and values of over-potential. The numerical validation is made by comparing with the available experimental results. Our results show that mixing efficiency can be enhanced by the combined effect of geometric modulation and surface potential heterogeneity. Linear stability analysis and energy budget analysis show that the periodic nature of velocity due to nonlinearity is predicted through phase diagram analysis.

Automated summary

This study examines the mixing performance in a modulated micro-channel filled with non-Newtonian power-law fluid by considering the combined effects of geometrical and surface potential heterogeneity. Analytical solutions are obtained for the electric potential and velocity, while Poisson-Nernst-Planck-Navier-Stokes equations are computed to evaluate the electroosmotic flow. The study shows that mixing efficiency can be enhanced by the combined effect of geometric modulation and surface potential heterogeneity.