Convective instability and mass transport of diffusion layers in a Hele-Shaw geometry

TL;DR

This study experimentally investigates the convective instability and mass transport in a Hele-Shaw cell with a density difference, revealing how finger formation enhances mixing and has implications for carbon sequestration.

Contribution

It provides detailed measurements of instability characteristics and mass transport rates in a porous medium flow, advancing understanding of convective mixing in geophysical applications.

Findings

Downward dense fingers significantly enhance mass transport.

Finger width and wave number are characterized for Ra between 6,000 and 90,000.

Results inform models of CO2 sequestration in aquifers.

Abstract

We consider experimentally the instability and mass transport of a porous-medium flow in a Hele-Shaw geometry. In an initially stable configuration, a lighter fluid (water) is located over a heavier fluid (propylene glycol). The fluids mix via diffusion with some regions of the resulting mixture being heavier than either pure fluid. Density-driven convection occurs with downward penetrating dense fingers that transport mass much more effectively than diffusion alone. We investigate the initial instability and the quasi steady state. The convective time and velocity scales, finger width, wave number selection, and normalized mass transport are determined for 6,000<Ra<90,000. The results have important implications for determining the time scales and rates of dissolution trapping of carbon dioxide in brine aquifers proposed as possible geologic repositories for sequestering carbon dioxide.