(210d) A Novel Experimental Method to Identify Reaction Region in Reactive Viscous Fingering

When a less-viscous fluid is injected into porous media or Hele-Shaw cells filled with a more-viscous fluid and it displaces the more-viscous fluid, an interface or boundary of the two fluids is unstable and forms finger-like pattern. This phenomenon is referred to as viscous fingering. When the two fluids are reactive, viscous fingering occurs accompanied with chemical reaction. The couplings between chemistry and fluid dynamics in reactive viscous fingering have been recently discussed since it has been reported that reactive viscous fingering is observed in several processes and plays an important role on the processes. However, clear understanding have not so far obtained on where and where the chemical reaction takes place during evolution of the fingering pattern. In this study, we describe a novel experimental method which enables us to identify where and when the reaction takes place in reactive viscous fingering. The method involves the switch of the less-viscous liquid injected. By using the method, we identify the reaction region at a given time under a certain experimental condition. We found that in the experimental condition the reaction region does not necessarily coincide with the region in which the product exists in the case where the reactive less-viscous liquid is continuously injected. The requirements for which the method is applicable are discussed.