Pore Network Simulation of Gas-Liquid Distribution in Porous Transport Layers

Pore network models are powerful tools to simulate invasion and transport processes in porous media. They are widely applied in the field of geology and the drying of porous media, and have recently also received attention in fuel cell applications. Here we want to describe and discuss how pore network models can be used as a prescriptive tool for future water electrolysis technologies. In detail, we suggest in a first approach a pore network model of drainage for the prediction of the oxygen and water invasion process inside the anodic porous transport layer at high current densities. We neglect wetting liquid films and show that, in this situation, numerous isolated liquid clusters develop when oxygen invades the pore network. In the simulation with narrow pore size distribution, the volumetric ratio of the liquid transporting clusters connected between the catalyst layer and the water supply channel is only around 3% of the total liquid volume contained inside the pore network at the moment when the water supply route through the pore network is interrupted; whereas around 40% of the volume is occupied by the continuous gas phase. The majority of liquid clusters are disconnected from the water supply routes through the pore network if liquid films along the walls of the porous transport layer are disregarded. Moreover, these clusters hinder the countercurrent oxygen transport. A higher ratio of liquid transporting clusters was obtained for greater pore size distribution. Based on the results of pore network drainage simulations, we sketch a new route for the extraction of transport parameters from Monte Carlo simulations, incorporating pore scale flow computations and Darcy flow

Investigation of spray agglomeration process in continuously operated horizontal fluidized bed

[EN] Spray fluidized bed agglomeration is an important process in particle formation and is widely used in the chemical, pharmaceutical and food industry. In this study a continuously operated horizontal fluidized bed is employed to obtain a continuous agglomeration process. It is conducted with glass beads (dst=200 µm) and water-based binder hydroxy-propyl-methyl-cellulose (HPMC) sprayed by three top nozzles. The steady state is reached and samples are taken periodically and analyzed. The influence of fluidization air temperature and configurations of internal weirs are studied.The authors gratefully acknowledge the funding of this work by the China Scholarship Council (NO. 201608130097).Du, J.; Bück, A.; Tsotsas, E. (2018). Investigation of spray agglomeration process in continuously operated horizontal fluidized bed. En IDS 2018. 21st International Drying Symposium Proceedings. Editorial Universitat Politècnica de València. 1855-1862. https://doi.org/10.4995/IDS2018.2018.7809OCS1855186

Pore network model of primary freeze drying

[EN] he pore scale progression of the sublimation front during primary freeze drying depends on the local vapor transport and the local heat transfer as well. If the pore space is size distributed, vapor and heat transfer may spatially vary. Beyond that, the pore size distribution can substantially affect the physics of the transport mechanisms if they occur in a transitional regime. Exemplarily, if the critical mean free path is locally exceeded, the vapor transport regime passes from viscous flow to Knudsen diffusion. At the same time, the heat transfer is affected by the local ratio of pore space to the solid skeleton. The impact of the pore size distribution on the transitional vapor and heat transfer can be studied by pore scale models such as the pore network model. As a first approach, we present a pore network model with vapor transport in the transitional regime between Knudsen diffusion and viscous flow at constant temperature in the dry region. We demonstrate the impact of pore size distribution, temperature and pressure on the vapor transport regimes. Then we study on the example of a 2D square lattice, how the presence of micro and macro pores affects the macroscopic progression of the sublimation front.Vorhauer, N.; Först, P.; Schuchmann, H.; Tsotsas, E. (2018). Pore network model of primary freeze drying. En IDS 2018. 21st International Drying Symposium Proceedings. Editorial Universitat Politècnica de València. 221-228. https://doi.org/10.4995/IDS2018.2018.7284OCS22122

Discrete modeling of ion transport and crystallization in layered porous media during drying

[EN] In this work, an isothermal pore network model has been utilized to investigate ion transport and crystallization in layerd porous media during drying. Said network consists of two distinct layers each with a different pore size distribution. One-dimensional approximation at the throat level describes transport phenomena for liquid, vapor, and dissolved salt. An explicit time stepping scheme has been used to obtain fluid pressure fields and ion concentration. Various simulations are carried out which indicate the effect of mean pore size disparity in the top and bottom layer, as well as the effect of drying rate on final crystal distribution.Rahimi, A.; Metzger, T.; Kharaghani, A.; Tsotsas, E. (2018). Discrete modeling of ion transport and crystallization in layered porous media during drying. En IDS 2018. 21st International Drying Symposium Proceedings. Editorial Universitat Politècnica de València. 299-306. https://doi.org/10.4995/IDS2018.2018.7415OCS29930

A pore-scale study on the drying kinetics and mechanical behavior of particle aggregates

[EN] A discrete thermo-mechanical drying model is developed to investigate the interaction between the porous structure and the drying characteristics of dense particle aggregates. The solid phase consists of polydisperse spherical particles in the micrometer range and the void space is constructed by a complementary network of tetrahedral pores. A modified version of the classical invasion percolation algorithm is set up to describe the preferential evaporation of the confined liquid in the pores. Thus, the evolution of the liquid distribution throughout the complex disordered medium can be simulated. In a one-way coupling scheme, capillary forces caused by both fluid pressure and surface tension are computed over time from the filling state of pores and they are applied as loads on each primary particle in the discrete element method. Based on this robust approach the drying kinetics and the mechanical behavior of several different aggregates with various fractions of small and large particles are simulated and quantified.Pham, TS.; Chareyre, B.; Tsotsas, E.; Kharaghani, A. (2018). A pore-scale study on the drying kinetics and mechanical behavior of particle aggregates. En IDS 2018. 21st International Drying Symposium Proceedings. Editorial Universitat Politècnica de València. 245-252. https://doi.org/10.4995/IDS2018.2018.7388OCS24525

Experimental investigation on pore size distribution and drying kinetics during lyophilization of sugar solutions

[EN] The pore structure is a decisive factor for the process efficiency and product quality of freeze dried products. In this work the two-dimensional ice crystal structure was investigated for maltodextrin solutions with different concentrations by a freeze drying microscope. The resulting drying kinetics was investigated for different pore structures. Additionally the three-dimensional pore structure of the freeze dried samples was measured by µ-computed tomography and the pore size distribution was quantified by image analysis techniques. The two- and three-dimensional pore size distributions were compared and linked to the drying kinetics.Foerst, P.; Lechner, M.; Vorhauer, N.; Schuchmann, H.; Tsotsas, E. (2018). Experimental investigation on pore size distribution and drying kinetics during lyophilization of sugar solutions. En IDS 2018. 21st International Drying Symposium Proceedings. Editorial Universitat Politècnica de València. 1415-1422. https://doi.org/10.4995/IDS2018.2018.7310OCS1415142

Research at the institute of process engineering at Otto von Guericke University Magdeburg

Seit der Gründung der Otto‐von‐Guericke‐Universität Magdeburg (OVGU) wurde der Forschungsbereich Verfahrenstechnik dort stetig ausgebaut. Heute umfasst die Fakultät für Verfahrens‐ und Systemtechnik der OVGU die vier Institute Verfahrenstechnik, Chemie, Strömungstechnik und Thermodynamik sowie Apparate‐ und Umwelttechnik. In diesem Beitrag stellen die fünf Lehrstühle des Instituts für Verfahrenstechnik (Bioprozesstechnik, Chemische Verfahrenstechnik, Systemverfahrenstechnik, Thermische Verfahrenstechnik und Mechanische Verfahrenstechnik) ihre Forschungsaktivitäten anhand ausgewählter Projekte vor

Разработка отклонителя для управления направлением скважин при ударно-вращательном бурении

Die Kombination einer Membran mit einer katalytischen Reaktion in einem Membranreaktor ist eines der Konzepte multifunktionaler Reaktoren zur Prozessintensivierung. Eine industriell besonders interessante Anwendung ist dabei die Darstellung von Synthesegas durch partielle Oxidation von Methan zu Kohlenmonoxid und Wasserstoff, wobei der Sauerstoff durch eine gemischtleitende Perowskit-Membran aus Luft zudosiert wird. Es ist gelungen, entsprechende Perowskit-Membranen als Hohlfasern mit einer volumenbezogenen Membranfläche von bis zu 500 m²/m³ durch einen ökonomischen Spinnprozess zu entwickeln. Unter Laborbedingungen konnten langzeitstabil Synthesegas (CO, H₂) mit einer CO-Selektivität von 95 % bei 95 % CH₄-Umsatz erzeugt und die Ergebnisse durch eine detaillierte mathematische Modellierung beschrieben werden. Copyright © 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim [accessed February 8th 2013