INFLUENCE OF THE ELECTRIC DOUBLE LAYER ON INDUCED PRESSURE FIELDS AND DEVELOPMENT LENGTHS IN ELECTRO-OSMOTIC FLOWS

Electro-osmotic flow can be used as an efficient pumping mechanism in microfluidic devices. For this type of flow, frictional losses at the entrance and exit can induce an adverse longitudinal pressure distribution that can lead to dispersive effects. The present study describes a numerical investigation of the influence of the electric double layer on the induced pressure field and the flow development length. The induced pressure gradient is affected by the volumetric flow rate, fluid viscosity and the channel height. When the electric double layer is small, the development length remains constant at 0.57 of the channel height but decreases as the double layer grows in thickness.

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Modeling of Electroosmotic Nanoflows With Overlapped Double Layer

ASME 2011 9th International Conference on Nanochannels, Microchannels, and Minichannels, Volume 2 ◽

10.1115/icnmm2011-58087 ◽

2011 ◽

Author(s):

Reza Nosrati ◽

Mehrdad Raisee ◽

Ahmad Nourbakhsh

Keyword(s):

Zeta Potential ◽

Double Layer ◽

Electric Double Layer ◽

Potential Distribution ◽

Present Model ◽

Ionic Concentration ◽

Channel Height ◽

Parabolic Profile ◽

Poisson Boltzmann ◽

Volume Method

In the present paper a new model is proposed for electric double layer (EDL) overlapped in nanochannels. The model aimed to obtain a deeper insight of transport phenomena in nanoscale. Two-dimensional Nernst and ionic conservation equations are used to obtain electroosmotic potential distribution in flow field. In the proposed study, transport equations for flow, ionic concentration and electroosmotic potential are solved numerically via finite volume method. Moreover, Debye-Hu¨ckle (DH) approximation and symmetry condition, which limit the application, are avoided. Thus, the present model is suitable for prediction of electroosmotic flows through nanochannels as well as complicated asymmetric geometries with large nonuniform zeta potential distribution. For homogeneous zeta potential distribution, it has been shown that by reduction of channel height to values comparable with EDL thickness, Poisson-Boltzmann model produces inaccurate results and must be avoided. Furthermore, for overlapped electric double layer in nanochannels with heterogeneous zeta potential distribution it has been found that the present model returns modified ionic concentration and electroosmotic potential distribution compare to previous EDL overlapped models due to 2D solution of ionic concentration distribution. Finally, velocity profiles in EDL overlapped nanochannels are investigated and it has been showed that for pure electroosmotic flow the velocity profile deviates from the expected plug-like profile towards a parabolic profile.

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Velocity measurements inside the diffuse electric double layer in electro-osmotic flow

Applied Physics Letters ◽

10.1063/1.2234836 ◽

2006 ◽

Vol 89 (4) ◽

pp. 044103 ◽

Cited By ~ 22

Author(s):

Reza Sadr ◽

Minami Yoda ◽

Pradeep Gnanaprakasam ◽

A. Terrence Conlisk

Keyword(s):

Double Layer ◽

Electric Double Layer ◽

Velocity Measurements ◽

Osmotic Flow ◽

Electro Osmotic Flow

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Experiments on Laminar Flow Development in Rectangular Ducts

Journal of Basic Engineering ◽

10.1115/1.3609536 ◽

1967 ◽

Vol 89 (1) ◽

pp. 116-123 ◽

Cited By ~ 44

Author(s):

E. M. Sparrow ◽

C. W. Hixon ◽

G. Shavit

Keyword(s):

Velocity Field ◽

Pressure Drop ◽

Cross Sections ◽

Pressure Field ◽

Working Fluid ◽

Aspect Ratios ◽

Pressure Fields ◽

Flow Development ◽

Pressure Development ◽

Axial Development

The development of the laminar velocity and pressure fields in the hydrodynamic entrance region of rectangular ducts has been explored experimentally. Duct cross sections having aspect ratios of 5:1 and 2:1 were employed in the investigation; air was the working fluid. It was found that the development of the pressure field is much more rapid than that of the velocity field. The entrance length, relative to pressure development, is representable as (z/De)/Re = 0.02 for both ducts. The incremental pressure drop due to the development of the flow was deduced from the experimental data as being approximately equal to one velocity head. The axial development of the velocity field is illustrated by a sequence of velocity profiles measured along the symmetry lines of the cross section. The flow development in the 5:1 duct is found to be somewhat more rapid than in the 2:1 duct. Comparisons of the experimental results are made with available predictions of analysis, all of which are based on approximate models of the flow field. In general, the analyses over predict the incremental pressure drop due to flow development. The development of the velocity field appears to be reasonably well described by analysis.

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Exact Solution of AC Electro-Osmotic Flow in a Microannulus

Journal of Fluids Engineering ◽

10.1115/1.4024205 ◽

2013 ◽

Vol 135 (9) ◽

Cited By ~ 13

Author(s):

Ali Jabari Moghadam

Keyword(s):

Exact Solution ◽

Double Layer ◽

Electric Double Layer ◽

Maximum Velocity ◽

Velocity Profiles ◽

Radius Ratio ◽

Dimensionless Frequency ◽

Ζ Potential ◽

Osmotic Flow ◽

Electro Osmotic Flow

The time-periodic electro-osmotic flow in a microannulus is investigated based on the linearized Poisson–Boltzmann equation. An exact solution of the velocity distribution is obtained by using the Green's function approach. The influences of the geometric radius ratio, the wall ζ potential ratio, the electrokinetic radius, and the dimensionless frequency on velocity profiles are presented. Variations of the geometric radius ratio (between zero and one) can lead to quite different flow behaviors. The wall ζ potential ratio affects the magnitude and direction of the velocity profiles within the electric double layer near the two walls of a microannulus. Depending on the frequency and the geometric radius ratio, the walls identically and/or oppositely charged, both may result in the two-opposite-direction flow in the annulus. For high frequency, the electro-osmotic velocity variations are restricted mainly within a thin layer near the two cylindrical walls. Increasing the electrokinetic radius leads to decrease the electric double layer thickness as well as the maximum velocity near the walls.

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