<title>Electroviscous effects in microchannels</title>

Abstract

Fluid flow in capillary microchannels is used in numerous applications in biotechnology (such as protein separation, fast DNA analysis, drug deliveries systems and viral filtration), in solid-state devices, and in catalytic devices. The current work presents the experimental validation for the electrokinetic theory in microchannels. Retardation of polar liquids, including de-ionized water, ethanol and propyl alcohol, is studied in microfabricated channels of several diameters.It was found that polar liquids flow about 6 percent more slowly than predicted by the classical hydrodynamic theory in microchannels, with the hydraulic diameter equal to 90 microns. For small microchannels with a hydraulic diameter of several microns, observed retardation is on the order of 70 percent. Collected experimental data have good correspondence with the electrokinetic model presented. Electrokinetic retardation of polar liquids in microchannels is based on the charge separation principle. Electrical charges are separated at the interface (near the channel wall). When liquid is forced downstream, it causes charge accumulation at one end of the microchannel. The streaming potential produced causes an upstream current that creates upstream counterfiow. The resultant fluid flow is less than it would be for non-polar liquids. The higher the zeta-potential at the microchannel wall and the smaller the channel, the larger the resulting retardation.Modifications for the friction factor, as applied to microfluidics, are suggested. Recommendations to improve fluid flow in microchannels are made.

A study of laminar flow of polar liquids through circular microtubes

“…Electroviscous effects of polar liquids in micron-sized channels is well documented. 10,11 In any case, this would result in an effective tube diameter, D eff ϭDϪ, were is the peak-to-valley roughness height. Using the data in Table I, the 30 gage tube would have an effective diameter of 159.5 m, rather than 163.5 m, corresponding to a 10% increase in Po.…”

The electric double layer effect on the microchannel flow stability and heat transfer

“…Well-controlled recent experiments have clearly confirmed that it can explain the behaviour of the Poiseuille number in the laminar regime, providing that the liquid contains a very small amount of ions [20]. Kulinsky et al [11] reported an increase of 70% of the friction factor under the EDL effect in planar channels of 4 µm heights with distilled water. Large thickness of the diffuse EDL layer of about 1 µm or more have been reported in these experiments.…”

Some effects of interface on fluid flow and heat transfer on micro- and nanoscale

“…Although the experiments on the EDL effect are few, its effects were proved. Kulinsky et al [66] reported an increment of 70% of the friction factor under the EDL effect in planar channels of 4 μm height with distilled water. Ren et al [67] made well-controlled experiments with three silicon channels with a height of 14.1, 29.2 and 40.5 µm and de-ionized ultra-filtered water and aqueous KCl.…”