A combined experimental and numerical analysis technique for velocity profiles in liquid microchannel flows is described. The working fluids employed are aqueous solutions with caged fluorescent dyes. A sheet of fluorescent dye is photo-injected by briefly exposing a cross-section of the fluid to ultraviolet light. The transport of the resulting ‘band’ of fluorescent dye is imaged onto a CCD camera using an epi-illumination fluorescent microscope system. The velocity profile is calculated from images acquired and processed after each uncaging event. The analysis technique utilizes several images, to provide velocity data with an increased signal-to-noise ratio. This combined experimental/numerical technique can provide velocity data in the near-wall region as well as in the bulk. Results are shown to compare favorably to analytical solutions in both pressure-driven and electroosmotic flow in circular cross-section capillaries of 205μm and 102μm inner diameters, respectively. Near-wall resolution is verified through application to electroosmotic flows with thin electrical double layers.

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