Sherwood number in porous microtube due to combined pressure and electroosmotically driven flow

Mass transfer of a neutral solute in a porous microtube is quantified in this study. An analytical expression of the Sherwood number is developed from first principles for combined flow of pressure driven and electroosmotic flow. Similarity solution method is adopted for solution of convective-diffusive species balance equation with coupled velocity profile, within the mass transfer boundary layer. It is observed that the Sherwood number increases with decrease in the Debye length (as the electric double layer becomes more compact) and it becomes constant beyond scaled Debye length of 60. Effects of the Reynolds number, dimensionless suction velocity, ratio of driving force and scaled Debye length have been investigated in detail. The analysis is useful for efficient design of microfluidic devices and flow through porous media.

This figure shows significant enhancement in Sherwood number with permeation velocity.Figure optionsDownload high-quality image (72 K)Download as PowerPoint slideHighlights
► Analytical solution of the Sherwood number is derived for a microtube.
► Sherwood number enhancement is up to κα=60 and remains constant thereafter.
► Increase in the Sherwood number is 8 times at dimensionless permeation velocity 200.
► Electric field opposing the flow decreases the Sherwood number.
► Analysis is valid for mass transfer boundary layer lies within 5% of tube radius.