Abstract
This paper presented an experimental validation of a numerical study on the vortical structures in AC electro-osmotic (ACEO) flows. First, the 3D velocity field of ACEO vortices above the symmetric electrodes was experimentally investigated using astigmatism microparticle tracking velocimetry. The experimentally obtained velocities were used to validate an extended nonlinear Gouy–Chapman–Stern model accounting for the surface conduction effect. A qualitative agreement between the simulations and experiments was found for the velocity field when changing AC voltage (from 0.5 to 2 V) and the frequency (from 50 to 3,000 Hz). However, the predicted magnitude of the velocity profiles was much higher than the experimentally obtained ones, except in some cases at low frequency. For frequencies higher than 200 Hz, a correction factor was introduced to make the numerical results quantitatively comparable to the experimental ones. In addition, the primary circulation, given in terms of the spanwise component of vorticity, was numerically and experimentally analyzed as function of frequency and amplitude of the AC voltage. The outline of the vortex boundary was determined via the eigenvalues of the strain-rate tensor estimated from the velocity field. It revealed that the experimental circulation was frequency dependent, tending to zero at both low and high frequency and the maximum changing from around 600 Hz for 1 V to 300 Hz for 2 V. The variation in the predicted vortex circulation as function of frequency and voltage, after using the above correction factor, was in good correspondence with the experiments. These results yield first insights into the characteristics of 3D ACEO flows and the ability of current numerical models to adequately describe them.
Similar content being viewed by others
References
Ajdari A (2000) Pumping liquids using asymmetric electrode arrays. Phys Rev E 61:R45–R48
Bazant MZ, Kilic MS, Storey BD, Ajdari A (2009) Towards an understanding of induced-charge electrokinetics at large applied voltages in concentrated solutions. Adv Colloid Interface Sci 152:48–88
Castellanos A, Ramos A, Gonzalez A, Green NG, Morgan H (2003) Electrohydrodynamics and dielectrophoresis in microsystems: scaling laws. J Phys D 36:2584–2597
Chen S, Angarita-Jaimes N, Angarita-Jaimes D, Pelc B, Greenaway AH, Towers CE, Lin D, Towers DP (2009) Wavefront sensing for three-component three-dimensional flow velocimetry in microfluidics. Exp Fluids 47:849–863
Cierpka C, Segura R, Hain R, Kähler CJ (2010) A simple single camera 3C3D velocity measurement technique without errors due to depth of correlation and spatial averaging for micro fluidics. Meas Sci Technol 21:045401
Cierpka C, Rossi M, Segura R, Kähler CJ (2010) On the calibration of astigmatism particle tracking velocimetry for microflows. Meas Sci Technol 22:015401
Das S, Chakrakorty S, Mitra SK (2012) Redefining electrical double layer thickness in narrow confinements: effect of solvent polarization. Phys Rev E 85:051508
Garcia D (2011) A fast all-in-one method for automated post-processing of PIV data. Exp Fluids 50:1247–1259
Green NG, Morgan H (1999) Dielectrophoresis of submicrometer latex spheres. 1. Experimental results. J Phys Chem B 103(1):41–50
Green NG, Ramos A, Gonzalez A, Morgan H, Castellanos A (2000) Fluid flow induced by nonuniform ac electric fields in electrolytes on microelectrodes. I. Experimental measurements. Phys Rev E 61:40114018
Green NG, Ramos A, Gonzalez A, Morgan H, Castellanos A (2002) Fluid flow induced by nonuniform ac electric fields in electrolytes on microelectrodes. III. Observation of streamlines and numerical simulation. Phys Rev E 66:026305
Gregersen MM, Andersen MB, Soni G, Meinhart C, Bruus H (2009) Numerical analysis of finite Debye-length effects in induced-charge electro-osmosis. Phys Rev E 79:066316
Jeong J, Hussain F (1995) On the identification of a vortex. J Fluid Mech 285:69–94
Khair AS, Squires TM (2008) Surprising consequences of ion conservation in electro-osmosis over a surface charge discontinuity. J Fluid Mech 615:323–334
Kilic MS, Bazant MZ, Ajdari A (2007) Steric effects in the dynamics of electrolytes at large applied voltages. II. Modified Poisson–Nernst–Planck equations. Phys Rev E 75:021503
Kim BJ, Yoon SY, Lee KH, Sung HJ (2009) Development of a microfluidic device for simultaneous mixing and pumping. Exp Fluids 46:85–95
Liu Z, Speetjens MFM, Frijns AJH, van Steenhoven AA (2014) Application of astigmatism μ-PTV to analyze the vortex structure of AC electroosmotic flows. Microfluid Nanofluid 16:553–569. doi:10.1007/s10404-013-1253-2
Lyklema J (1995) Solid–liquid interfaces, Vol. II of Fundamentals of interface and colloid science. Academic Press, San Diego
Morgan H, Green NG (2002) AC electrokinetic: colloids and nanoparticles. Research Studies Press, Hertfordshire
Olesen LH, Bruus H, Ajdari A (2006) AC electrokinetic micropumps: the effect of geometrical confinement, faradaic current injection, and nonlinear surface capacitance. Phys Rev E 73:056313
Ramos A, Morgan H, Green NG, Castellanos A (1998) AC electrokinetics: a review of forces in microelectrode structures. J Phys D Apply Phys 31:2338–2353
Ramos A, Morgan H, Green NG, Castellanos A (1999) AC electric field-induced fluid flow in microelectrodes. J Colloid Interface Sci 217:420–422
Ramos A, Gonzalez A, Castellanos A, Green NG, Morgan H (2003) Pumping of liquid with ac voltage applied to asymmetric pairs of microelectrodes. Phys Rev E 67:056302
Soni G, Squires TM, Meinhart CD (2007) Nonlinear phenomena in induced charge electroosmosis. In: 2007 ASME international mechanical engineering congress and exposition, Seattle, USA
Speetjens MFM, Wispelaeere HNL, van Steenhoven AA (2011) Multi-functional Lagrangian flow structures in three-dimensional ac electro-osmotic micro-flows. Fluid Dyn Res 43:035503
Storey BD, Edwards LR, Kilic MS, Bazant MZ (2006) Steric effects on ac electro-osmosis in dilute electrolytes. Phys Rev E 77:036317
Vollmers H (2001) Detection of vortices and quantitative evaluation of their main parameters from experimental velocity data. Meas Sci Technol 12:1199–1207
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Liu, Z., Speetjens, M.F.M., Frijns, A.J.H. et al. Validated numerical analysis of vortical structures in 3D AC electro-osmotic flows. Microfluid Nanofluid 16, 1019–1032 (2014). https://doi.org/10.1007/s10404-014-1377-z
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s10404-014-1377-z