Measurement of dissolved oxygen diffusion coefficient in a microchannel using UV-LED induced fluorescence method

Abstract

The diffusion coefficient of dissolved oxygen (DO) was measured in a microchannel using the UV-LED induced fluorescence method. Mass transfer between oxic and anoxic de-ionized (DI) water was quantitatively visualized in a Y-shaped microchannel. Oxygen-sensitive ruthenium (tris (2,2′-bipyridine) ruthenium (II) chloride hexahydrate] and a 450-nm UV-LED were used for the optical measurement of a DO concentration field. In situ pixel-by-pixel calibration was carried out to obtain Stern–Volmer equations to measure the DO concentration field with a spatial resolution of 0.625 μm/pixel. The diffusion layers are successfully acquired for different Reynolds numbers (Re = 0.14, 1.4, and 14). The DO diffusion coefficient is calculated by both the constant-assumed and the concentration-dependent diffusion coefficient methods. The measured DO diffusion coefficient, 2.32 × 10−9 m2/s, is very close to that of the theoretical prediction of the oxygen gas diffusion coefficient, 2.16 × 10−9 m2/s.