Freezing and ice aging dynamics in saline water under natural convection

TL;DR

This study investigates the long-term evolution of saline ice, revealing how desalination and porosity changes influence ice dynamics through coupled heat, mass transfer, and fluid flow, supported by experiments and theoretical modeling.

Contribution

It introduces a comprehensive one-dimensional model that predicts saline ice aging by coupling phase change, desalination, and convective fluid flow effects.

Findings

Desalination reduces porosity and alters thermal equilibrium.

Ice thickness decreases slowly due to desalination-driven buoyancy weakening.

The model accurately predicts long-term ice evolution across parameter ranges.

Abstract

Understanding the coupled dynamics of liquid-solid phase change and fluid flows is crucial in a wide range of geophysical and industrial applications. When freezing occurs in saline water, the newly formed ice is mushy, with a porous structure that traps the brine within the ice. In this work, which combines experiments and theoretical analyses, we investigate the long-term evolution of saline ice, comprehensively accounting for the coupled dynamics of multiscale fluid flow, heat and mass transfer, and phase change. We show that in a closed convective system the rapid formation of a mushy ice layer is followed by desalination (i.e, the expulsion of salt from the ice) processes that might lead to a slow asymptotic decrease of the ice thickness. Desalination of mushy ice reduces its porosity, which alters the dynamic thermal equilibrium and ice thickness by weakening buoyancy-driven convection within the mushy layer. In turn, changes in brine convection and ice thickness affect the further desalination of the ice. The long-term dynamics of the system can be accurately predicted by a one-dimensional model based on appropriate parameterizations of global heat and mass transfer properties. Furthermore, within the same theoretical model we explore the ice dynamics across a broader parameter space. Our findings advance the understanding of the coupled phase-change physics of saline solutions in the presence of convective fluid flows and provide a basis for explaining and predicting real-world phenomena such as the aging of sea ice.