Thermodynamic Analysis of Bistability in Rayleigh-Bénard Convection

Momentum transport of morphological instability in fluid displacement with changes in viscosity

Saffman-Taylor instability exhibits a stepwise unstable morphology from a stable interface to viscous fingering, eventually leading to tip splitting. The nonlinear dynamics of the destabilized interface depends on various flow properties. However, the physicochemical mechanism that determines the transition point of the flow state is unclear. We studied the interfacial instability transition in miscible displacement from a thermodynamic perspective by calculating the momentum transport and entropy production. Using numerical analysis based on Darcy's law coupled with the convection-diffusion equation, the observed flux-dependent flow state transitions were attributed to the selection of the flow state with a higher entropy production.

Tunable Hydrodynamic Interfacial Instability by Controlling a Thermodynamic Parameter of Liquid-Liquid Phase Separation

Herein, we report on the hydrodynamic interfacial instability controlled by a thermodynamic parameter driving the liquid-liquid phase separation during fluid displacement in a Hele-Shaw cell. This instability remains even when the solution is guaranteed to be hydrodynamically stable. Adjusting the salt concentration helps control the miscibility of the solutions and change the pattern of the interface. We observe stable circular, fingering, and droplet formation patterns as the salt concentration is decreased from equilibrium. In addition, we analyze this interfacial instability using thermodynamic flux, which is determined from the growth rate of the interface, and provide a theoretical framework to quantitatively predict the transition points between the patterns. We find that the patterns transition to a state having higher entropy production.