GRK 2160 DROPIT: Upscaling of coupled free-flow and porous-media-flow processes

(Zeitschriften-) Aufsätze

1. Michalkowski, C., Veyskarami, M., Bringedal, C., Helmig, R., & Schleper, V. (2022). Two-phase Flow Dynamics at the Interface Between GDL and Gas Distributor Channel Using a Pore-Network Model. Transport in Porous Media, 144(2), 429--458. https://doi.org/10.1007/s11242-022-01813-4
   • Zusammenfassung
   • BibTeX
   • Link

   Zusammenfassung

   For improved operating conditions of a polymer electrolyte membrane (PEM) fuel cell, a sophisticated water management is crucial. Therefore, it is necessary to understand the transport mechanisms of water throughout the cell constituents especially on the cathode side, where the excess water has to be removed. Pore-scale modeling of diffusion layers and gas distributor has been established as a favorable technique to investigate the ongoing processes. Investigating the interface between the cathode layers, a particular challenge is the combination and interaction of the multi-phase flow in the porous material of the gas diffusion layer (GDL) with the free flow in the gas distributor channels. The formation, growth and detachment of water droplets on the hydrophobic, porous surface of the GDL have a major influence on the mass, momentum and energy exchange between the layers. A dynamic pore-network model is used to describe the flow through the porous GDL on the pore-scale. To capture the droplet occurrence and its influence on the flow, this dynamic two-phase pore-network model is extended to capture droplet formation and growth at the surface of the GDL as well as droplet detachment due to the gas flow in the gas distributor channels. In this article, the developed model is applied to single- and multi-tube systems to investigate the general drop behavior. These rather simple test-cases are compared to experimental and numerical data available in the literature. Finally, the model is applied to a GDL unit cell to analyze the interaction between two-phase flow through the GDL and drop formation at the interface between GDL and gas distributor channel.

   BibTeX

   @article{michalkowski_two-phase_2022, abstract = {For improved operating conditions of a polymer electrolyte membrane (PEM) fuel cell, a sophisticated water management is crucial. Therefore, it is necessary to understand the transport mechanisms of water throughout the cell constituents especially on the cathode side, where the excess water has to be removed. Pore-scale modeling of diffusion layers and gas distributor has been established as a favorable technique to investigate the ongoing processes. Investigating the interface between the cathode layers, a particular challenge is the combination and interaction of the multi-phase flow in the porous material of the gas diffusion layer (GDL) with the free flow in the gas distributor channels. The formation, growth and detachment of water droplets on the hydrophobic, porous surface of the GDL have a major influence on the mass, momentum and energy exchange between the layers. A dynamic pore-network model is used to describe the flow through the porous GDL on the pore-scale. To capture the droplet occurrence and its influence on the flow, this dynamic two-phase pore-network model is extended to capture droplet formation and growth at the surface of the GDL as well as droplet detachment due to the gas flow in the gas distributor channels. In this article, the developed model is applied to single- and multi-tube systems to investigate the general drop behavior. These rather simple test-cases are compared to experimental and numerical data available in the literature. Finally, the model is applied to a GDL unit cell to analyze the interaction between two-phase flow through the GDL and drop formation at the interface between GDL and gas distributor channel.}, author = {Michalkowski, Cynthia and Veyskarami, Maziar and Bringedal, Carina and Helmig, Rainer and Schleper, Veronika}, doi = {10.1007/s11242-022-01813-4}, issn = {1573-1634}, journal = {Transport in Porous Media}, month = {9}, number = 2, pages = {429--458}, title = {Two-phase Flow Dynamics at the Interface Between GDL and Gas Distributor Channel Using a Pore-Network Model}, url = {https://doi.org/10.1007/s11242-022-01813-4}, volume = 144, year = 2022 }

   Link

   https://doi.org/10.1007/s11242-022-01813-4
2. Ackermann, S., Bringedal, C., & Helmig, R. (2021). Multi-scale three-domain approach for coupling free flow and flow in porous media including droplet-related interface processes. Journal of Computational Physics, 429, 109993. https://doi.org/10.1016/j.jcp.2020.109993
   • Zusammenfassung
   • BibTeX
   • Link

   Zusammenfassung

   Drops on a free-flow/porous-medium-flow interface have a strong influence on the exchange of mass, momentum and energy between the two macroscopic flow regimes. Modeling droplet-related pore-scale processes in a macro-scale context is challenging due to the scale gap, but might be rewarding due to relatively low computational costs. We develop a three-domain approach to model drop formation, growth, detachment and film flow in a lower-dimensional interface domain. A simple upscaling technique allows to compute the drop-covered interface area fraction which affects the coupling fluxes. In a first scenario, only drop formation, growth and detachment are taken into account. Then, spreading and merging due to lateral fluxes are considered as well. The simulation results show that the impact of these droplet-related processes can be captured. However, extensions are necessary to represent the influence on the free flow more precisely.

   BibTeX

   @article{ackermann-bringedal-helmig-2021, abstract = {Drops on a free-flow/porous-medium-flow interface have a strong influence on the exchange of mass, momentum and energy between the two macroscopic flow regimes. Modeling droplet-related pore-scale processes in a macro-scale context is challenging due to the scale gap, but might be rewarding due to relatively low computational costs. We develop a three-domain approach to model drop formation, growth, detachment and film flow in a lower-dimensional interface domain. A simple upscaling technique allows to compute the drop-covered interface area fraction which affects the coupling fluxes. In a first scenario, only drop formation, growth and detachment are taken into account. Then, spreading and merging due to lateral fluxes are considered as well. The simulation results show that the impact of these droplet-related processes can be captured. However, extensions are necessary to represent the influence on the free flow more precisely.}, author = {Ackermann, Sina and Bringedal, Carina and Helmig, Rainer}, doi = {https://doi.org/10.1016/j.jcp.2020.109993}, issn = {0021-9991}, journal = {Journal of Computational Physics}, month = {3}, pages = 109993, publisher = {Elsevier BV}, title = {Multi-scale three-domain approach for coupling free flow and flow in porous media including droplet-related interface processes}, url = {http://www.sciencedirect.com/science/article/pii/S0021999120307671}, volume = 429, year = 2021 }

   Link

   http://www.sciencedirect.com/science/article/pii/S0021999120307671