Thermo-hydro-mechanical modeling of pore-fluid phase change in porous media

• Ein thermohydromechanisches Modell zur Beschreibung des Phasenwechsels von Porenfluide in porösen Medien

Sweidan, Abdel Hassan; Markert, Bernd (Thesis advisor); Meschke, Günther (Thesis advisor)

Aachen : RWTH Aachen University (2022)
Book, Dissertation / PhD Thesis

In: Report. IAM, Institute of General Mechanics 15
Page(s)/Article-Nr.: 1 Online-Ressource : Illustrationen

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2022

Abstract

Due to accelerating climate changes and the presence of more extreme weather conditions, the topic of freezing-induced damage had become more important, especially in connection with infrastructure damages and slope stability. In cold regions, soils underneath pavement or concrete foundations may experience frost damage due tofreezing-thawing cycles. Besides, employing artificial ground freezing (AGF) technology in soft soils for providing temporary ground support during tunnel excavation or controlling the groundwater during geotechnical construction can lead to permanent heave-induced damages. On the other hand, recourse to various forms of renewable energy has become of great concern due to the limited non-renewable energy resources and increased environmental awareness. However, most renewable energy sources are intermittent, unpredictable, and only available at certain periods. Hence, efficient thermal energy storage is necessary to increase the overall efficiency and provide better reliability. Latent energy storage using phase change materials (PCMs) is considered one of the most efficient ways of storing energy. Since most PCMs suffer from low thermal conductivity, various techniques, such as highly conductive porous metals, could be incorporated to enhance their thermal conductivity and heat storage rates. This work aims to investigate coupled thermo-hydro-mechanical processes, which occur during the phase change in fluid-saturated porous media. In particular, a thermodynamically-consistent formulation is introduced leading to a novel phase-field thermo-hydro-mechanical (P-THM) approach. The model macroscopically describes a biphasic porous medium, consisting of a non-isothermal and incompressible porous matrix and a pore-fluid. The constituents are in a state of local thermal non-equilibrium, and the model proceeds from the small-strains assumption of the deformable elastic solid skeleton. The governing equations are based on the well-founded continuum mechanical theory of porous media (TPM) extended by the phase-field modeling (PFM) approach, where the model accounts for the temperature evolution, fluid phase transitions, fluid-solidinteractions, and the associated volumetric deformations. A key merit of the PFM approach is its feasibility within standard finite element frameworks, where it does not explicitly track the moving boundaries (interfaces) of the phase-change constituent. Of particular importance in the underlying work is the PFM-based unified kinematics treatment of the solid and liquid phases of the pore-fluid. Furthermore, a demonstration of the micro-cryo-suction mechanism during soil freezing and its realization in the continuum model through a phenomenological retention-curve-like formulation is presented. This enables the modeling of ice lens formation and stiffness degradation in the thermal (quasi-) steady state based on a suction-induced phase-field fracture approach. The model is further extended to describe the freezing process in partially saturated soil as a triphasic medium considering the water and gas (air) phases. The presented numerical examples and comparisons demonstrate the ability, reliability, and usefulness of theproposed modeling framework in describing the phase-change process in porous media under thermal loading.