News
New Publication: A comparative study on the Lattice Boltzmann Method and the VoF-Continuum method for oxygen transport in the anodic porous transport layer of an electrolyzer
Dasika Prabhat Sourya, Pardha S. Gurugubelli, Supriya Bhaskaran, Nicole Vorhauer-Huget, Evangelos Tsotsas, Vikranth Kumar Surasani
https://doi.org/10.1016/j.ijhydene.2024.10.340
The optimization of Polymer Electrolyte Membrane (PEM) electrolyzers necessitates an intimate knowledge of the oxygen flows within the anodic porous transport layers (PTLs) to determine any possible reduction in performance. In this field, as experimental studies are cumbersome and expensive, numerical modeling has arisen as a viable alternative for studying the oxygen transport within the Anodic PTLs of a PEM electrolyzer. Amongst the various numerical modeling techniques, the Lattice Boltzmann Method (LBM) is gaining prominence for its effectiveness in analyzing fluid transport within porous media due to its mesoscopic nature and ease of implementation. This study utilizes the Shan-Chen LBM methodology to model the flow of oxygen within the Anodic PTL of a PEM electrolyzer and compares it against the Volume-of-Fluid-based Continuum Model. The results show that LBM can not only replicate the experimental studies accurately, but can also maintain its high accuracy at progressively shrinking length scales of PTLs, even at length scales where the VoF-based Continuum Model would run into accuracy issues. The high accuracy of the LBM model, combined with the simplicity of the LB algorithm makes LBM a powerful technique for simulating the microfluidic flows such as the flow of oxygen within the Anodic PTL of a PEM electrolyzer.
New Publication: Pore-scale study of coupled heat and mass transfer during primary freeze-drying using an irregular pore network model
Felix Faber, Nicole Vorhauer-Huget, Maximilian Thomik, Sebastian Gruber, Petra Foerst, Evangelos Tsotsas
https://doi.org/10.1080/07373937.2024.2407062
This study presents a pore network (PN) model with transient heat transfer and quasi-steady transitional vapor transport that is for the first time applied to irregular porous structures that are obtained by reconstruction of X-ray tomography image data. In contrast to previous studies, the irregular pores are not approximated by spheres but implemented in their original shape. Secondly, instead of assuming cylindrical throats as pore connections, the actual distance between pore centers as well as the pore cross sections are used for the computation of the vapor transport coefficient. The control volume elements of the computational model are matched with the cells obtained by Voronoi tessellation. The improvements have clear advantages over former approaches where the reconstructed void space is usually strongly simplified by balls and sticks confined in a regular lattice structure. A freeze-dried sample of maltodextrin DE12 with 20% (w/w) solid content is used for benchmarking the new methodology. Its morphological and thermal properties are determined by the novel PN model. The simulation results of primary freeze-drying (FD) are compared to reference cases in two ways. First, the differences in heat and mass transfer kinetics as compared to regular PNs are emphasized. Secondly, the PN simulation results are confronted with a simple literature model that neglects pore size distribution (PSD) and transient heat transfer. It is shown that already in small domains with relatively narrow PSD, the variation of the mass transfer coefficient affects the computed sublimation fluxes and yields a significant deviation from the simpler literature model. Moreover, it is revealed in this study that the structure has a significant impact on the sublimation front temperature. This is demonstrated by the comparison of FD in the irregular PN to a regular PN with almost identical PSD but different porosity. The development, verification, and benchmarking of the new PN model can be seen as an important step for studies of the structure dependence of FD.
New Publication: Evaluation of Convective Heat Transfer Inside the Pores of Pyrolyzed Wood using a µ-CT Based Realistic Geometry
Andrea Dernbecher, Supriya Bhaskaran, Nicole Vorhauer-Huget, Jakob Seidenbecher, Suresh Gopalkrishna, Lucas Briest, and Alba Dieguez-Alonso
http://dx.doi.org/10.1007/978-3-031-66609-4_36
This work investigates the impact of the realistic porous structure of a biomass particle on the intraparticle convective transport. To this end, the porous structure of a biomass particle pyrolyzed at 300°C as characterized with X-ray microtomography and a realistic reconstruction of the microstructure was used for pore-resolved computational fluid dynamics (CFD) simulations of the flow. Based on these simulation results, local interfacial heat transfer coefficients in the pores were evaluated. This is a first step to derive macroscopic effective parameters that describe the intraparticle transport taking into account the complex anisotropic microstructure and morphology of the particle, as well as its evolution during the pyrolytic conversion process.
New Publication: Pore shape matters – In-situ investigation of freeze-drying kinetics by 4D XCT methods
Sebastian Gruber, Joshua Greiner, Alexander Eppink, Maximilian Thomik, Frederik Coppens, Nicole Vorhauer-Huget, Evangelos Tsotsas, Petra Först
https://doi.org/10.1016/j.foodres.2024.114837
CRC/TRR 287 BULK-REACTION Funding Period 2
The CRC/TRR 287 BULK-REACTION is granted for 4 more years by the Deutsche Forschungsgemeinschaft DFG between 2024 and 2028.
The CRC is a Trans-Regio project between the Otto-von-Guericke-University Magdeburg, Ruhr University Bochum, Technical University Dortmund and Christian-Albrechts-University Kiel. The main goal of the CRC is the examination of reacting moving granular assemblies with gas flow, which is an important unit operation in energy process engineering.
Two research projects, from Neda Kazemi and Felix Faber, contribute to the CRC with research against waste and usage of renewable energies for heating applications.
Further reading can be found here.
New Publication: Model PEM water electrolyzer cell for studies of periodically alternating drainage/imbibition cycles
Supriya Bhaskaran, Tamara Miličić, Tanja Vidaković-Koch, Vikranth Kumar Surasani, Evangelos Tsotsas, Nicole Vorhauer-Huget
https://doi.org/10.1016/j.ijhydene.2024.06.268
Investigating the counter-current two-phase flow within the anodic porous transport layer (PTL) of polymer electrolyte membrane water electrolyzers (PEMWEs) is a complex yet intriguing challenge. Until now, the gasliquid invasion processes inside PTLs are only to a limited extent accessible under operation conditions, usually using sophisticated and expensive optical approaches, i.e., neutron imaging. We propose a model-supported experimental method with a fully operating microfluidic PEMWE, that allows to examine pore-scale oxygenwater distributions at the anode with high spatial and temporal resolution. The microfluidic cell is made of transparent Poly-Methyl-Methacrylate (PMMA), and the PTL is simplified by a quasi-2D pore network (PN) with a uniform pore-throat structure in the first preliminary study. The proposed setup is a significant advancement over previous studies, where gas was only injected at a constant flow rate from a single point. Test cases with current densities of 0.1, 1, and 2 A/cm2 and water flow rates of 1, 3, 5, and 10 ml/min were realized in the novel setup. We found periodically alternating invasion of oxygen (drainage) and water (imbibition), which were analyzed based on image sequences as well as voltage measurements. The experimental data is additionally supported by pore-scale Lattice Boltzmann (LB) and PN simulations. The preliminary results with the simplified PN structure are used to study the dominating transport mechanisms, revealing that drainage and imbibition occur simultaneously and are affected by evaporation and wetting liquid films formed in sharp pore corners. These phenomena are also expected to occur in more complex PTL structures. The preliminary results can, therefore, be regarded as an important basis for PTL studies, which are structurally more complex.