InterPore2025

Boundaries regulates convection, dispersion and solid-liquid phase change in porous media under Rayleigh-Darcy convection

19 May 2025, 17:40

15m

Oral Presentation (MS06-B) Interfacial phenomena across scales MS06-B

Speaker

Dr Ke Xu (Peking University)

Description

Rayleigh-Darcy (R-D) convection emerges when fluid density at the top is higher than that at the bottom in a porous stratum. This density mismatch may be induced by geothermal gradient or concentration contrast during CO2 or mineral dissolution. R-D convection largely determines the vertical heat and mass transfer, and may significantly reshape the porous matrix.

Here we introduce our recent experimental, numerical and theoretical works on some interesting phenomena correlated to interface and boundary effects during R-D convection. These works include:

1) Solid dissolution that induces R-D convection. When the porous matrix contains soluble components (such as ice in permafrost beneath salt water, carbonate in sandstone with acid environment, and oil sand reservoir under solvent extraction), we experimentally observe fingering dissolution interface at low Rayleigh number (Ra) and stable dissolution interface at high Ra. We theoretical rationalize this observation by the competition between horizontal dispersion and vertical circumflex, which controls the growth rate of interface perturbation.

2) Vertical transport efficiency with non-straight boundary. Vary few works discussed how non-straight boundary affect R-D convection. We conduct numerical simulations with one boundary a sine curve. As expected, wavy boundary regulates the large-scale convection envelope. However, this regulation of convection results in different modification of vertical transfer behaviors compared to that with straight boundary: when Ra < 1300, vertical transport efficiency is enhanced by the wavy boundary; when Ra>10000, vertical transport efficiency is suppressed by the wavy boundary. We rationalizes these two regimes by the evolution of bottom stable stream under different Ra .

3) Horizontal dispersion coefficient of a passive scalar under R-D convection. We surprisingly observe that although convection keeps intensifying with Ra, horizontal dispersion coefficient scales with Ra only in a narrow regime, and keeps unchanged when Ra > 2500. We rationalize this two-stage dispersion coefficient variation: at low Ra, passive scalar migrates through stable bulk circumflex; at high Ra, boundary layer with dynamic micro-plumes becomes dominant horizontal transport channel. Dimensionless analysis reveals the dependence of ultimate dispersion coefficient with Lewis number and molecular diffusivity.