The Study On Determination For The Diffusion Coefficient In Micro-channels By Chemical Color Reaction

A new microfluidic device was described in this paper. The multiphase laminar flow determination device was drived by gravity. It makes possible that a diffusional transfer of an analyte from a sample stream into a stream of a "receiver" fluid. The concentration gradient is affected by the transverse diffusion from a flow with analyte into a flow initially without analyte. To optimize sensitivity, the mathematical method is probed at a position in which molecular diffusion across the boundary of the two flows has been minimal, just after the flow initially without analyte merges with the flow initially containing the analyte at a given concentration. According to the diffusion law and hydrodynamics principle, only if Re is less than 2000, when liquid through the micro-channel of width for 400μm and depth for 40μm, only control liquid flow rate less than 0.050m/s.The experiment aimed at optimizing experimental conditions, at the same time determining the diffusion coefficient at different ion and concentration when the temperature was 293K-353K. The practicability of the experiment and device was proved by the calculation of flow rate and diffusion coefficient.The diffusion coefficient at different concentration and temperature were determined in sodium hydroxide and phenolphthalein reaction system, ferric nitrate and ammonium thiocyanate reaction system, lead nitrate and xylenol orange reaction system, as well as potassium dichromate and diphenlycarbazide reaction system. The activation energy was also calculated according to Arrhenius formula. The experimental results indicated that the diffusion coefficient will largen when the temperature is risen or the concentration is increased.