Diffusivity ratio effect on the onset of the buoyancy-driven instability of an A plus B → C chemical reaction system in a Hele-Shaw cell: Numerical simulations and comparison with experiments

The effect of different diffusivities on the evolution of buoyancy-driven instability in a reactive-diffusion system is analyzed. For an instantaneous A + B -> C chemical reaction in a Hele-Shaw cell, where a less dense phase of A is layered on top of a denser solution of B, the temporal evolution of the instability motion is traced numerically by using the Fourier spectral method. As expected, the evolution of instabilities can be controlled by chemical factors, such as the ratios of diffusivities, reactant concentrations, and densification coefficients. Double diffusive effects accelerate and hinder the evolution of instabilities and induce the onset of instabilities without an adverse density gradient. The present numerical simulation explains the previous experiments for the NH3 + CH3COOH -> CH3COONH4 reaction in a Hele-Shaw cell, which was devised to explain the impact of the chemical reaction in geological CO2 sequestration. Published under license by AIP Publishing.