This paper describes a flow reversal phenomenon for fluids with moderate conductivity. Fluids with conductivities of 2 × 10−4 S/m, 0.02 S/m and up to 0.1 S/m were experimented at frequencies ranging from 1 to 110 kHz. Flow reversal was observed only at ~1 kHz and 5.3 Vrms for σ = 0.02 S/m, and our analysis indicates that AC electrothermal effect could be responsible. Analysis of the system impedance and simulation of power consumption show that the distribution of electric power consumption is dependent on conductivity and AC frequency. At low frequencies, possibly more electric power is consumed at surface/electrolyte interface rather than within the fluid, which consequently changes the location of temperature maximum and the directions of temperature gradients. The direction of AC electrothermal force is reoriented, causing the flow reversal. Numerical simulation is also performed and agrees within the experiments.
Microfluidics Flow reversal AC electrothermal effect
This is a preview of subscription content, log in to check access.
The project has been supported by the US National Science Foundation under grant number ECS-0448896.
Castellanos A, Ramos A, González A, Green NG, Morgan H (2003) Electrohydrodynamics and dielectrophoresis in microsystems: scaling laws. J Phys D Appl Phys 36:2584–2597CrossRefGoogle Scholar
Gonzalez A, Ramos A, Morgan H, Green NG, Castellanos A (2006) Electrothermal flows generated by alternating and rotating electric fields in microsystems. J Fluid Mech 564:415–433zbMATHCrossRefMathSciNetGoogle Scholar
Green NG, Ramos A, Gonzalez A, Castellanos A, Morgan H (2000a) Electric field induced fluid flow on microelectrodes: the effect of illumination. J Phys D Appl Phys 33:L13–L17CrossRefGoogle Scholar
Green NG, Ramos A, Gonzalez A, Morgan H, Castellanos A (2000b) Fluid flow induced by nonuniform ac electric fields in electrolytes on microelectrodes. I. Experimental measurements. Phys Rev E 61:4011–4018CrossRefGoogle Scholar
Green NG, Ramos A, Gonzalez A, Castellanos A, Morgan H (2001) Electrothermally induced fluid flow on microelectrodes. J Electrostat 53:71–87CrossRefGoogle Scholar
Gregersen M, Olesen L, Brask A, Hansen M, Bruus H (2007) Flow reversal at low voltage and low frequency in a microfabricated ac electrokinetic pump. Phys Rev E 76:056305CrossRefGoogle Scholar
Kilic MS, Bazant MZ (2007) Steric effects in the dynamics of electrolytes at large applied voltages. I. Double-layer charging. Phys Rev E 75:021502CrossRefGoogle Scholar
Lastochkin D, Zhou R, Wang P, Ben Y, Chang H-C (2004) Electrokinetic micropump and micromixer design based on ac faradaic polarization. J Appl Phys 96(3):1730–1733CrossRefGoogle Scholar
Lian M, Wu J (2009) Ultra fast micropumping by biased alternating current electrokinetics. Appl Phys Lett 94:064101CrossRefGoogle Scholar
Lian M, Islam N, Wu J (2006) Particle line assembly/patterning by microfluidic AC electroosmosis. J Phys Conf Ser 34:589–594CrossRefGoogle Scholar
Lian M, Islam N, Wu J (2007) AC electrothermal manipulation of conductive fluids and particles for lab-chip applications. IET Nanobiotechnol 1(3):36–43CrossRefGoogle Scholar
Lide DR (2000) CRC handbook of chemistry and physics, 81st edn edn. CRC, New YorkGoogle Scholar
Perch-Nielsen IR, Green NG, Wolff A (2004) Numerical simulation of traveling wave induced electrothermal fluid flow. J Phys D Appl Phys 37:2323–2330CrossRefGoogle Scholar
Ramos A, Morgan H, Green NG, Castellanos A (1998) AC electrokinetics: a review of forces in microelectrode structures. J Phys D Appl Phys 31:2338–2353CrossRefGoogle Scholar
Storey BD, Edwards LR, Kilic MS, Bazant MZ (2008) Steric effects on ac electro-osmosis in dilute electrolytes. Phys Rev E 77:036317CrossRefGoogle Scholar
Studer V, Pepin A, Chen Y, Ajdari A (2004) An integrated AC electrokinetic pump in a microfluidic loop for fast and tunable flow control. Analyst 129:944–949CrossRefGoogle Scholar
Urbanski JP, Thorsen T, Levitan JA, Bazant MZ (2006) Fast AC electro-osmotic pumps with non-planar electrodes. Appl Phys Lett 89:143508CrossRefGoogle Scholar
Wu J, Ben Y, Battigelli D, Chang H (2005a) Long-range AC electrokinetic trapping and detection of bioparticles. Ind Eng Chem Res 44(8):2815–2822CrossRefGoogle Scholar
Wu J, Ben Y, Chang H-C (2005b) Particle detection by micro-electrical impedance spectroscopy with asymmetric-polarization AC electroosmotic trapping. Microfluid Nanofluidics 1(2):161–167CrossRefGoogle Scholar
Yang K, Wu J (2008) Investigation of microflow reversal by AC electrokinetics in orthogonal electrodes for micropump design. Biomicrofluidics 2:024101CrossRefMathSciNetGoogle Scholar