III International Conference

PP-III-30MRI STUDY OF ADVECTION-CONVECTION INFLUENCE ON CHEMICALWAVES PROPAGATIONZhivonitko V.V., Koptyug I.V.International Tomography Center, Novosibirsk, RussiaE-mail: v_zhivonitko@tomo.nsc.ruThe present work deals with MRI investigation of reagents transport as well asconvective flows influence on chemical waves in different media, such as packed bed and thincapillary. Three autocatalytic chemical systems were studied: cobalt(II)-hydrogen peroxidesystem, iron(II)-nitric acid system and chlorite-thiosulfate system. For the cobalt(II)-hydrogenperoxide system qualitative data are gained. For the iron(II)-nitric acid system chemical wavevelocity vs average fluid flow linear dependence is obtained. According to it, wave velocity isnot the additive sum of flow velocity and front velocity without any reagents transport. Forthe first time NMR-thermometry is employed in order to visualize wave propagation inchlorite-thiosulfate system.Traveling waves in liquid-phase attract great interest because of their thermodynamicalimportance. The reaction-diffusion model, which is the theoretical base of wave activityorigin in autocatalytic reactions, is used for the description of many biological, medical andgeophysical phenomena. On the other hand, investigation of wave dynamics in open systemsgives information about mutual influences of chemical reaction and reagents transport, whichis important for chemical engineering.The main goal of the present work is to gain general experimental data about interactionsbetween chemical waves and flows of different nature in various media. Experiments wereperformed by means of magnetic resonance imaging (MRI), apparently the only techniquesuitable for the purpose. Three wave active chemical systems were examined: oxidation ofCo 2+ ethylenediamine complex by H 2 O 2 (cobalt(II)-hydrogen peroxide system), oxidation ofFe 2+ by nitric acid (iron(II)-nitric acid system) and oxidation of S 2 O 2- 3 by NaClO 2 (chloritethiosulfatesystem).In the MRI experiment with iron(II)-nitric acid system acquiring of contrasted imageswas based on the difference in paramagnetic properties of Fe 2+ and Fe 3+ ions. Experimentswere performed in a packed-bed reactor and a thin capillary. In both cases it was found thatwave velocity dependence on average flow velocity has a linear character. Experimental datafor the packed-bed reactor are presented in the Figure 1 along with two extreme cases. It isobvious from the graph, that front velocity is not a sum of flow velocity and wave velocitywithout any reagent transport, so it looks like wave velocity is adjusting to the alternation of524