Combined electroosmosis-pressure driven flow and mixing in a microchannel with surface heterogeneity

Abstract

a b s t r a c tWe investigate the combined pressure-driven electroosmotic flow near a wall roughness in the form of a rectangular block mounted on one wall of an infinitely long microchannel. The insulated rectangular block has a constant surface potential which is different from the surface potential of the remaining part of the channel walls. The characteristics for the electrokinetic flow are obtained by numerically solving the Navier-Stokes equations coupled with the Nernst-Planck equation for ion transport and the Poisson equation for electric field. Vortical flow develops above the block when the surface potential of the block is in opposite sign to that of the surface potential of the channel. The strength of the re-circulating vortex grows as the surface potential of the block increases. Vortical flow also depends on the Debye length when it is in the order of the channel height. The combined effects due to the geometrical modulation of the channel wall and heterogeneity in surface potential is found to produce a stronger vortex and hence a stronger mixing, as compared with the effect of either of these. The recirculating vortex, which appears on the upper face of the block, grows and the average electroosmotic velocity increases with the increase of the electrolyte concentration. The recirculating vortex does not appear when EDL is thick and the effect of over-potential of the block on electroosmosis is negligible. The loss of momentum near the obstacle is compensated by the electrostatic force near the EDL, which prevents flow separation upstream or downstream of the obstacle. The mixing performance of the present configuration is compared with several other cases of surface modulation. The impact of the imposed pressure gradient on the vortical flow due to surface heterogeneity is analyzed.

Analysis of electro-osmotic flow in a microchannel with undulated surfaces

“…The analytical model (40) shows a strong non-linear dependency on important quantities such as dielectric constant ε, temperature T , and salt concentration C 0 , all through the inverse Debye length κ defined in Eq. (23). We plot in Fig.…”

“…Along with the expectations for engineering applications, fundamental research relevant to electrokinetic phenomena in small-scale systems, ranging from nano-to micrometers, has also attracted attention [6][7][8][9][10][11][12][13][14][15]. Particularly, the advances in observing and processing techniques have prompted research focusing on surface properties such as roughness and structure [16][17][18][19][20][21][22][23].…”

Pressure-Driven Electro-Osmotic Flow and Mass Transport in Constricted Mixing Micro-Channels

“…Ebrahimi et al (2014) studied mixing and heat transfer characteristics of pressure drivenelectro-osmotic flow in a T-shaped micro-channel by carrying out a numerical simulation and predicted some means to improve efficiency of mixing in micro-channel. Bhattacharyya and Bera (2015) numerically investigated pressure-driven electroosmotic flow in an infinitely long micro-channel with surface roughness.…”

Investigation of slip effects on electroosmotic mixing in heterogeneous microchannels based on entropy index

“…Furthermore, the mixing performance of electro osmotic flows has been examined for both passive and active micro-mixers [25,26]. Studies of electrokinetic mixing are mostly performed using Nernst-Planck equations [11,26,27] and there are a few investigations in which Helmholtz-Smoluchowski model [12][13][14] has been used to evaluate the mixing performance. On the other hand, examination of the results of Helmholtz-Smoluchowski model for mixing efficiency at various conditions indicates that this model can be used with acceptable accuracy if Debye-Hückel parameter and wall zeta-potential are properly selected [20,28].…”