An Experimental and Numerical insight into Diffusive Zones in Radial Miscible Viscous Fingering *

Displacement of a high viscous fluid by a less viscous one in a porous medium deforms the interface into finger like patterns, a hydrodynamic instability termed as viscous fingering (VF). Many researchers have carried out research to understand VF due to its application in a variety of fields viz., enhanced oil recovery, CO₂ sequestration, mixing industry, point-of-care devices, to name a few. The growth of VF patterns is known to demonstrate the proportionate growth in humans. A recent study experimentally reported a diffusion dominated zone following the one dominated by convection for radial displacement of miscible fluids. Diffusion is known to stabilize miscible VF and diffusive effects are strong during initial stages of flow when concentration gradient is high. Thus, a diffusion dominated zone is anticipated before convection overtakes and results in VF. However, this initial diffusion driven zone is missing in literature. We provide experimental as well as numerical evidences for this zone for a variety of radial displacements with a point source and a finite source containing both the fluids inside the Hele-Shaw cell.