Thermally induced velocity gradients in electroosmotic microchannel flows: the cooling influence of optical infrastructure

Thermally induced velocity gradients in electroosmotic microchannel flows: the cooling influence... An axially non-uniform temperature distribution is shown to induce a disturbance to the electroosmotic flow field in microchannels, causing a significant deviation from the ideal plug-like velocity profile. Such axial temperature gradients are shown to be induced passively by the increased dissipation of Joule heat through the optical infrastructure of a viewing window. A combination of caged-dye-based molecular tagging velocimetry (to determine the cross-stream velocity profiles), fluorescence-based thermometry (to determine the in-channel fluid temperatures), and electrical current measurements are employed. The temperature visualization experiments demonstrate that the fluid is locally cooled in the viewed region, resulting in a local increase in the electric field strength. When large fields are applied, measurements indicate that the fluid’s temperature in the viewed region can be as much as 30°C less than in the remainder of the capillary. Despite an increase in viscosity, this local cooling results in a locally increased electroosmotic wall velocity which induces a concave velocity profile in the viewed portion and a convex velocity profile elsewhere. Experimentally determined profiles exhibit a variation in velocity across the channel of up to 5%. The cause of this velocity profile curvature is confirmed by comparing the velocity profiles obtained at a range of fields to an analytical solution that includes the effects of temperature on the liquid conductivity and viscosity. Experiments in Fluids Springer Journals

Thermally induced velocity gradients in electroosmotic microchannel flows: the cooling influence of optical infrastructure

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Copyright © 2004 by Springer-Verlag
Engineering; Engineering Fluid Dynamics; Fluid- and Aerodynamics; Engineering Thermodynamics, Heat and Mass Transfer
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