CFD‐Simulation zur Berechnung der durch Gewebestrukturen induzierten Strömungsfelder mithilfe der Immersed‐boundary‐Methode

Woven structures are often used for separation of solid particles. The solid phase is separated when the fluid flows through the woven structure. Knowing the nature of the flow can be profitably used for the optimization of these structures (e.g., reduction of the pressure loss) and to predict the separation efficiency. In general, computational fluid dynamics allows the calculation of the flow field. In this paper, the immersed boundary method is shown as an efficient way to simulate the flow field within woven structures and reduce modeling efforts compared to the standard CFD method.     

Untersuchung der Strömung im Taylor‐Couette‐System bei geringen Spaltbreiten

The shaft bushings in many machines form a Taylor‐Couette system with a thin clearance. The flow in such a clearance was studied in this paper by means of CFD simulation. Two different gap width ratios have been chosen to investigate the flow from laminar to turbulent range. Based on the simulation results a critical gap width ratio is determined in the turbulent regime, which is of importance to the transition of a turbulent flow with Taylor vortex in a turbulent flow without Taylor vortex.     

Spillover‐bedingte Reichweite von aktivierten Sauerstoffatomen in der katalytischen Rußoxidation an Nanopartikel‐Schichtsystemen

The catalytic oxidation of carbon particles is an important process, e.g., in regeneration of diesel particulate filters. If the catalyst and the carbon particles are not in direct contact, a transportation step of the activated oxygen atoms (oxygen spillover) is needed. The distance of oxygen spillover in a nanoparticle layer system was studied. The system consisted of a platinum catalyst (20 μm thick) and a carbon (300 μm thick) layer that were separated by an inert SiO₂ layer with variable thickness. At moderate conversion (< 40 %), which occurs without substantial structural changes of the carbon particle layer, a distance of 160 μm was found. The spillover distance of the oxidizing species may be a starting point for the geometric design of more efficient impregnated catalytic particulate filters.     

Absorption von CO2 mittels wässriger Natronlauge – Experimente und Simulationen mit dem Ansatz der Hydrodynamischen Analogien

An approach for the simulation of separation processes in packed columns is based on hydrodynamic analogy between complex flow pattern in real equipment units and geometrically simplified model flow and is known as the Hydrodynamic Analogy (HA) approach. In this work, the HA approach was applied to reactive absorption of CO₂ in aqueous sodium hydroxide solution under turbulent gas flow conditions. An extensive experimental study was carried out to measure the CO₂ concentration profiles along the column height. These data provided a basis for a successful validation of the HA approach.     

Modellierung und Simulation von Strömungen und biologischen Reaktionen innerhalb eines Belebtschlammbeckens

With the aim to increase the efficiency of the aeration tanks of municipal wastewater treatment plants, the implementation of a biological model system (ASM1) into the CFD code ANSYS CFX® is presented for modeling a full‐scale aeration tank and verified with experimental data. Taking into account the biological processes, hydrodynamics and gas‐liquid mass transfer, simulations were performed and compared to experimental concentration profiles for ammonium and nitrate. The assumptions made are explained in detail. While the simulated ammonium concentration profile is in good agreement with the measured values, deviations occur for the nitrate profile. However, the CFD simulations exceed the prediction accuracy of conventional 0D simulation software.     

Untersuchung der Strömungsformen im Spalt zwischen einer rotierenden Scheibe und einer ruhenden Gegenscheibe

The flow in the gap between a rotating and a parallel static opposite disk is simulated for a small gap width and without flow rate by using computational fluid dynamics. The velocity distribution for different flow regimes is presented. Based on the simulation results the velocity profiles in the turbulent region with “separate boundary layers” are described by approximate equations.     

Verbesserte Simulation der Temperaturentwicklung von HT‐PEM‐Brennstoffzellen zur Effizienzsteigerung

Identification and prevention of large temperature gradients can extend the lifespan of fuel cells. Estimating the temperature distribution during operation is difficult because of the complex processes in the cell. Therefore, even with large computational power only small and simple flow field geometries can be calculated yet. The integration of a new mathematical formulation in commercial simulation software allows calculation and assessment of complex geometries in order to increase their efficiency and lifespan.     

SkaSim – Skalierbare HPC‐Software für molekulare Simulationen in der chemischen Industrie

This article outlines advances in molecular modeling and simulation using massively parallel high‐performance computers (HPC). In the SkaSim project, partners from the HPC community collaborated with users from science and industry. The aim was to optimize the prediction of thermodynamic property data in terms of efficiency, quality and reliability using HPC methods. In this context, various topics were dealt with: atomistic simulation of homogeneous gas bubble formation, surface tension of classical fluids and ionic liquids, multicriteria optimization of molecular models, the development of the molecular simulation codes ls1 mardyn and ms2, atomistic simulation of gas separation processes, molecular membrane structure generators, transport resistors and the evaluation of predictive property data models based on specific mixture types.     

Numerische Simulation disperser Gas/Flüssig‐Strömungen in Blasensäulen bei hohen Gasgehalten mit OpenFOAM®. Teil 2 – Numerische Simulation und Ergebnisse

The design of industrial gas/liquid reactors such as bubble columns requires detailed information with respect to the flow structure and characteristics of two‐ or multiphase systems in the reactor. The contribution is focused on the evaluation of the simulation results obtained by a selection of models. The results are further compared with those reported in literature. The simulations have been performed with the CFD software OpenFOAM®. The main focus of the numerical simulation was set on capturing the characteristic process and design parameters of bubble columns.     

Numerische Untersuchungen interkalationsinduzierter Spannungen in Elektrodeneinzelpartikeln von Lithium‐Ionen‐Batterien

A challenge in the further development of lithium ion batteries is the reduction of the measurable capacity fade. One mechanism leading to electrode degradation is particle cracking due to the intercalation of lithium into the host material. This leads to considerable volumetric strain, and therefore, to mechanical stresses which can exceed the particle strength. In order to estimate the magnitude of the arising intercalation‐induced stresses, a numerical model was developed for a single particle consisting of LiCoO₂. Special consideration was paid to the influence of phase segregation on mechanical stresses. A three dimensional model was developed in order to cover the influence of anisotropic particles with spheroids used as model system.     

Numerische Simulation disperser Gas/Flüssig‐Strömungen in Blasensäulen bei hohen Gasgehalten mit OpenFOAM® Teil 1 – Grundlagen der Modellierung

Various chemical products are synthesized in processes using gas/liquid reactors with bubbly flows. Hence, there is significant interest in a more efficient process design as well as in process intensification with a strong focus on this reactor class. However, the design of industrial gas/liquid reactors requires more detailed information about the flow structures and characteristics of two‐ or multiphase systems. The basic models for two‐fluid model simulations of dispersed gas/liquid flows in bubble columns at high gas fractions are presented..     

CFD‐Simulation der Feststoffeinbindung in einen Sprühstrahl

Sound‐absorbing mats consisting of cross‐linked Polyurethane (PUR) foam and metal reinforcements, door panels and centre consoles for the interior of vehicles became important products for automotive component suppliers. The leading technology for the production of foam on the base of PUR with noise absorbing properties is the application of powder insertion (e.g. metal) in the PUR spray. The numerical simulation (CFD) of the spray including the particle‐droplet interaction is presented. The theoretical background of the implemented models is explained and the experimental results achieved with a pilot plant are compared with the numerical results. The presented simulation offers the possibility to suitably predict the metal powder distribution in a PUR spray.     

Untersuchung der CO2‐Absorptionskinetik in wässrigen Lösungen von N,N‐Diethylethanolanmin und N‐Ethylethanolamin

N‐Ethylethanolamine (EEA) and N,N‐diethylethanolamine (DEEA) represent promising alkanolamines for CO₂ removal from gaseous streams, as they can be prepared from renewable resources. In this work, the reaction rate constant for the reaction between CO₂ and EEA and the liquid‐side mass transfer coefficient were determined from the absorption rate measurements in a blend comprising DEEA, EEA and H₂O. A stirred‐cell reactor was applied for the absorption studies, whereas a zwitterion mechanism for EEA and a base‐catalyzed hydration mechanism for DEEA were used to describe the reaction kinetics.     

Inline‐Bestimmung der CO2‐Beladung von wässrigem Diglykolamin in Abhängigkeit von Viskosität und Temperatur

The solvents CO₂ loading is an important factor when evaluating the efficiency of an absorption/desorption process. There is almost no possibility to measure the CO₂ loading inline. Therefore experiments were made to determine a correlation between the CO₂ loading and the solvents viscosity as well as the solvents temperature. The correlation was verified using control tests and values from the literature. An overall maximum relative error under 10 % could be observed. Simultaneously investigations were made to understand if the solvents electrical conductivity and pH value are suitable for a similar correlation.