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A new adaptive procedure for using chemical probes to characterize mixing

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The iodide-iodate chemical probe method is modified by a novel adaptive procedure to investigate the mixing abilities of two compact curved-duct reactors. Both reactors have a rectangular cross section; the first has smooth curvature (called the wavy duct) and the second has sharper bends (zigzag duct). In the conventional procedure, this method is used to characterize local micro-mixing, and for all experiments (for different Reynolds numbers and injection points) the reagent initial concentrations are kept at the same values. Even with wall injection, the selectivity of the chemical system is generally improved by increasing the flow Reynolds number. Nevertheless, two limitation sencountered in using chemical probes (with the conventional protocol) tocharacterize the mixing abilities of the present reactors that prevent the conventional protocol of the chemical probe from discriminating between the mixing abilities of the two mockups. First, the duct walls are corrugated, so that the wall injection used to measure local micro-mixing is affected by the wall roughness, independently of the Reynolds number. Second, the flow Reynolds numbers are relatively low due to the small size of the duct sides, so that the measurements are inevitably hindered by meso-mixing effects. The challenge is thus to adapt the chemical method for characterizing the global mixing, by enlarging the measurement volumes o as to capture and take into account all mixing scales. In the new adaptive procedure, the kinetics of the second reaction are adjusted in such away as to impose the same reactive volume for different Reynolds numbers, leading to more relevant results for the segregation index XS. Experimental results reveal that the mixing performance of the zigzag channel as assessed by this method is slightly above that of the wavy one. Finally, these gregation indexin both reactor sisrelated to the mixing time tm by using a physical model in the literature. (C) 2011 ElsevierLtd. All rights reserved.

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