Measurement of dissolved oxygen diffusion coefficient in a microchannel using UV-LED induced fluorescence method
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RESEARCH PAPER
Measurement of dissolved oxygen diffusion coefficient in a microchannel using UV-LED induced fluorescence method Juan Chen • Hyun Dong Kim • Kyung Chun Kim
Received: 30 June 2012 / Accepted: 22 September 2012 / Published online: 3 November 2012 Ó Springer-Verlag Berlin Heidelberg 2012
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 (2,20 -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 lm/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 9 10-9 m2/s, is very close to that of the theoretical prediction of the oxygen gas diffusion coefficient, 2.16 9 10-9 m2/s. Keywords UV-LED induced fluorescence (ULIF) method Microchannel DO concentration field Diffusion layer thickness Virtual origin DO diffusion coefficient
1 Introduction Detection of dissolved oxygen (DO) in water is of considerable interest for a wide variety of applications. DO is a key substrate in many fields. The DO concentration in a body of water is a primary indicator of water quality. J. Chen H. D. Kim K. C. Kim (&) School of Mechanical Engineering, Pusan National University, Busan 609-735, Republic of Korea e-mail: [email protected]
The biological activity in a body of water is directly related to the DO concentration. The delivery of a controlled oxygen supply and accurate sensing of dissolved oxygen levels within a miniaturized environment is a necessity in biological assay, bioreactors, and tissue engineering applications. A controllable source of oxygen is a key constraint on cellular growth and development in tissue engineering applications (Vollmer et al. 2005). Thus, real-time measurement and predictive control of DO concentration is one of the most effective methods of monitoring the treatment process and is widely studied in relation to activated sludge wastewater treatment processes (Han et al. 2012), cell culture (Mehta et al. 2007), fermentation processes (Gomes and Menawat 2000), and laboratory-scale bioreactors (Diaz et al. 1996). Therefore, efficient control of the dissolved oxygen transport rate can contribute to increasing the overall productivity of the process. Designing an effective control strategy for controlling DO requires the precise measurement of DO concentration. Conventional methods of DO concentration measurement are discussed by Gogate and Pandit (1999). These methods consist of
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