Abstract
The aims of this study are to visualize gas diffusion process between gas–liquid interface and measure a diffusion coefficient of dissolved oxygen in water by using a microscale UV-LED-induced phosphorescence method. The mass transfer between air and water was visualized qualitatively in a Y-shaped microchannel and the diffusion coefficient D L was measured quantitatively. Oxygen-sensitive phosphorescence dye (tris (2, 2′-bipyridine) ruthenium (II) chloride hexahydrate) and a 450 nm UV-LED were used for the optical measurement of a dissolved oxygen concentration (DOC) field. In-situ pixel-by-pixel calibration was carried out to obtain Stern–Volmer constant and phosphorescent intensity was converted to DOC field with a spatial resolution of 0.625 μm/pixel. Instantaneous dissolved oxygen concentration field and diffusion coefficient D L were successfully measured and compared to the theoretical prediction based on the one-dimensional Fick’s law. It was confirmed that the experimental results were in good agreement with the numerical prediction.
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