Peking University, April 17, 2025: Using permafrost melting as a model system, Xu Ke's research team from the Department of Energy and Resources Engineering, Peking University, has made significant progress in the theory of solid-liquid phase transition in porous media. The related findings were recently published in Science Advances.
Fig. 1. Experimental setup.
Why it matters
(i) With global warming causing sea levels to rise, saline seawater and industrial wastewater are accelerating permafrost degradation.
(ii) While salt lowers water’s freezing point, the detailed mechanisms driving thaw patterns were previously unclear.
(iii) Rapid thaw increases the risk of methane leakage (a potent greenhouse gas) and pollutant spread, which are crucial considerations for climate modeling.
Experimental Setup and Observations
(i) The team built a visual experimental system to study the melting interface in a controlled porous medium.
(ii) Two melting behaviors were identified:
• Fingering instability: Irregular, channel-like melting under low permeability, low density contrast, and shallow depths.
• Smooth Fronts: Uniform downward melting under high permeability, greater density contrast, and deeper layers.
(iii) A key finding: the melting rate depends on the Darcy number, a relationship not captured by existing theoretical models.
Fig. 2. Two melting modes of ice in porous media under saline water: Top row shows fingering instability at low Rayleigh number; bottom row shows flat melting interface at high Rayleigh number.
Mechanisms Driving Melting Modes
(i) Two competing flow mechanisms influence melting:
• Bottom circulation: Local flows shaped by the interface promote fingering.
• Rayleigh-Darcy convection: Large scale mixing flow smooths out the interface.
(ii) The transition between these modes was modeled using numerical simulations.
Broader impacts
These insights also have implications for CO₂ storage, oil recovery, magma evolution, and extraterrestrial ice resource studies.
*This article is featured in PKU News "Why It Matters" series. More from this series.
Click "here" to read the paper
Written by: Akaash Babar
Edited by: Zhang Jiang
Source: Department of Energy and Resources Engineering, Peking University
