A Colorful Mixing Experiment in a Stirred Tank Using Non-Newtonian Blue Maize Flour Suspensions

• Autores: Grissel Trujillo-de Santiago, Cecilia Rojas-de Gante, Silverio García Lara, Adriana Ballesca Estrada, Mario Moises Alvarez
• Localización: Journal of chemical education, ISSN 0021-9584, Vol. 91, Nº 10, 2014, págs. 1729-1735
• Idioma: inglés
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• Resumen

  • A simple experiment designed to study mixing of a material of complex rheology in a stirred tank is described. NonNewtonian suspensions of blue maize flour that naturally contain anthocyanins have been chosen as a model fluid. These anthocyanins act as a native, wide spectrum pH indicator exhibiting greenish colors in alkaline environments, blue tones in neutral conditions, and pink- violet colors in acid environments. Students used a continuous injection of a basic solution in an initially acidic environment to reveal mixing patterns and flow structures and to follow their evolution over time in a typical stirred tank configuration. These experiments aim to demonstrate, in a laboratory setting, basic concepts related to mixing: (i) the existence of mixing pathologies in laminar-stirred tanks; (ii) the complex rheology of some real suspensions; (iii) the effect of tank geometry on mixing performance; and (iv) the quantitation of mixedness and mixing evolution using digital color analysis.