(667a) Local Structure of a Reactive Flow Field on Miscible Viscous Fingering with Chemical Reaction

This is the successive study of Nagatsu et al. submitted to AIChE Annual Meeting 2006. Nagatsu (one of the authors) and Ueda performed experiments on reactive miscible viscous fingering in a Hele-Shaw cell (Nagatsu and Ueda, AIChE Journal 47, 1171-1720 (2001)). In the experiments, an instantaneous chemical reaction takes place which produces the product which is visibly recognized by difference in color. Also, the reaction has no influence on hydrodynamics of the fingering. They showed that the product distribution significantly depends on the ratio between reactant concentrations initially included in the more- and less-viscous liquids normalized by a stoichiometric ratio of the chemical reaction, j_v. For j_vj_v>>1 it concentrates around the tips of the fingers. In Nagatsu and Ueda (2001) they also conducted theoretical analysis on a concentration field of chemical species in two liquids with different viscosities by using a simplified one-dimensional diffusion-reaction model. Analytical results showed that the reaction plane is located in the less-viscous liquid far from the interface between the two liquids for j_vj_v>>1. We, therefore, concluded that the dependence of the product distribution is caused by the difference in the location of the reaction plane due to j_v. In these experiments, however, one can not exactly recognize where and when the reaction takes place since the region where the product exists does not necessarily coincide with the region where the reaction takes place. This is because the region where the product exist at a given time may indicate that the product produced in early times remains at the given time although the reaction does not takes place at the given time. In this study we attempt to identify where and when the reaction takes place for each condition of j_v by means of the novel experimental method involving the switch of the less-viscous liquid injected which will be presented by Nagatsu et al. in AIChE Annual Meeting 2006. We found that in early times during evolution of the fingering pattern the reaction takes place at entire region of the small fingering regardless of j_v, while as time proceeds the reaction region becomes to depend on j_v. For j_vj_v>>1, the reaction takes place in the troughs and insides of fingers and does remarkably in the tips of fingers. In addition, we found that the shielded fingers are the region where the reactive less-viscous liquid is not supplied and the reaction does not take place.