Mixing and reaction processes of two reactive liquids in an eccentric annular flow

Mixing and reaction processes of two reactive liquids in glycerin contained in a cylindrical vessel with an eccentric cylindrical rod were experimentally investigated. The eccentricity, defined as the distance between the centers of the vessel and the rod normalized by the difference between the radii of the vessel and the rod was varied between 0.1 and 0.7. The cylindrical vessel and the cylindrical rod were rotated alternately was keeping the Stokes flow condition. Ferric nitrate (Fe(NO₃)₃) and potassium ferrocyanide (K₄[Fe(CN)₆]) were used as reactants, resulting in the following reaction: Fe³⁺+K₄[Fe(CN)₆] → KFe[Fe(CN)₆]+3 K⁺ Since the product (KFe[Fe (CN)₆]) is dark blue in color, the region where it is present can be identified. This reaction is so fast compared to the flow motion that it occurs as soon as two reactants mix in a molecular scale. The heat of reaction is small enough to treat the chemical reaction as passive with regard to the flow motion. The chemical reaction is significantly enhanced in the chaotic region and the reaction region gradually spreads over the chaotic region, regardless of the initial location of reactants. The chemical reaction is much enhanced when reactants are placed in the region where the stretching rate of elements is much larger.