Anna Mareike Kostelecky

arXiv2026

A dynamic pore-network model with discrete microbubble transport

We develop a hybrid pore-network model (PNM) for discrete microbubble transport coupled to connected two-phase flow in porous media. We apply the model to simulate flow in the porous transport layer of a rotating proton exchange membrane (PEM) electrolyser. At sufficiently large apparent gravitational forces, bubbles growing at the catalyst layer can detach at sizes smaller than the characteristic pore size and move through liquid-filled pores via buoyancy and advection. The model couples a dynamic two-phase PNM to a Lagrangian bubble tracker. Pore-scale Stokes simulations in square throats provide closures for the bubble buoyancy velocity, the hydraulic resistance of bubble-occupied throats, and the reciprocal coupling between liquid flow and bubble motion. Verification tests assess conservation, pressure-flow coupling, bubble growth, advection, merging, trapping, and transfer to the connected gas phase. The network simulations show that increasing apparent gravitational forces shifts a larger fraction of the produced gas toward discrete-bubble transport. The increase mostly comes from a reduced detachment radius, which decreases bubble size and lets them move more freely through the network.

cs.CE↗

arXiv2025

Local Thermal Non-Equilibrium Models in Porous Media: A Comparative Study of Conduction Effects

Instantaneous heat transfer between different phases is a common assumption for modeling heat transfer in porous media, known as Local Thermal Equilibrium (LTE). This assumption may not hold in certain technical and environmental applications, especially in systems with large temperature gradients, large differences in thermal properties, or high velocities. Local Thermal Non-Equilibrium (LTNE) models aim to describe heat transfer processes when the LTE assumption may fail. In this work, we compare three continuum-scale models from the pore to the representative elementary volume (REV) scale. Specifically, dual-network and REV-scale models are evaluated against a pore-resolved model, which we perceive as a reference in the absence of experimental results. Different effective models are used to obtain upscaled properties on the REV scale and to compare resulting temperature profiles. The systems investigated are fully saturated, consisting of one fluid and one solid phase. This study focuses on purely conductive systems without significant differences in thermal properties. Results show that LTE holds then for low interfacial resistances. However, for large interfacial resistances, solid and fluid temperatures differ. The REV-scale model with effective parameters obtained by homogenization leads to similar results as the pore-resolved model, whereas the dual-network model shows greater deviation due to its fixed spatial resolution. Among the evaluated effective parameter formulations for the REV-scale model, only the homogenization-based approach captures the LTNE behavior, as it incorporates the interfacial heat transfer coefficient. Convection is relevant for most practical applications, and its impact will be addressed in a follow-up article.

physics.flu-dyn↗