Abstract:
The displacement of a less viscous fluid by a more viscous fluid in a radial Hele-Shaw
cell makes a circular pattern because the interface is hydrodynamically stable in this condition.
Very recently, it has been experimentally reported that the hydrodynamically stable displacement in a
partially miscible system induces fingering patterns while stable circular patterns are made at fully
miscible and immiscible systems. The fingering instability in the partially miscible system results
from complex and entangled elements involving viscous dissipation, molecular diffusion, and phase
separation. The analyzing mechanism requires a quantitative relationship between the hydrodynamic
interfacial fingering patterns and underlying physicochemical properties. Here, we experimentally
investigated the change in fluid patterns formed by the progression of phase separation in the partially
miscible systems and categorized them into three patterns: finger-like pattern, annular-like pattern,
and circular pattern. Moreover, we propose the mechanism of the pattern formation by an interfacial
tension measurement and evaluate the patterns by modified capillary number and newly defined
body force ratio, Bf
. Our analysis revealed that the deformation index of the pattern can be expressed
as a function of Bf on a single curve regardless of the miscibility
