Influence of different silica nanoparticles on drop size distributions in agitated liquid‐liquid systems

The impact of different silica nanoparticles on rheology, interfacial tension and drop size distributions in liquid‐liquid systems is determined experimentally. The particles vary in wettability and specific surface area. In contrast to commonly used high‐energy devices for Pickering emulsion preparation, low energy input by stirring allows to quantify drop breakage and coalescence in steady state and dynamic conditions. The experiments can provide essential information for drop size model development in nanoparticle‐stabilized emulsions.DFG, 56091768, TRR 63: Integrierte chemische Prozesse in flüssigen MehrphasensystemenTU Berlin, Open-Access-Mittel - 201

Validation of pressure drop prediction and bed generation of fixed‐beds with complex particle shapes using discrete element method and computational fluid dynamics

Catalytic fixed‐bed reactors with a low tube‐to‐particle diameter ratio are widely used in industrial applications. The heterogeneous packing morphology in this reactor type causes local flow phenomena that significantly affect the reactor performance. Particle‐resolved computational fluid dynamics has become a predictive numerical method to analyze the flow, temperature, and species field, as well as local reaction rates spatially and may, therefore, be used as a design tool to develop new improved catalyst shapes. Most validation studies which have been presented in the past were limited to simple particle shapes. More complex catalyst shapes are supposed to increase the reactor performance. A workflow for the simulation of fixed‐bed reactors filled with various industrially relevant complex particle shapes is presented and validated against experimental data in terms of bed voidage and pressure drop. Industrially relevant loading strategies are numerically replicated and their impact on particle orientation and bed voidage is investigated.TU Berlin, Open-Access-Mittel – 202

Impact of Contact Scaling and Drag Calculation on the Accuracy of Coarse‐Grained Discrete Element Method

The accuracy of coarse‐grained discrete element method (CGDEM) relies on appropriate scaling rules for contact and fluid‐particle interaction forces. For fluidized bed applications, different scaling rules are used and compared with DEM results. The results indicated that in terms of averaged values as mean particle position and voidage profile, the coupling of computational fluid dynamics and CGDEM leads to accurate results for low scaling factors. Regarding the particle dynamics, the approach leads to an underestimation of RMS values of particle position indicating a loss of particle dynamics in the system due to coarse graining. The impact of cell cluster size on drag force calculation is studied. The use of energy minimization multiscale drag correction is investigated, and a reduced mesh dependency and good accuracy are observed.TU Berlin, Open-Access-Mittel – 202

Partikelaufgelöste CFD als Werkzeug für die mehrskalige Designuntersuchung zur Prozessintensivierung in schlanken Festbetten

Slender fixed-bed reactors are widely used in the chemical industry, especially in the field of heterogeneous catalysis. This reactor type is characterized by strong heterogeneities in bed morphology that cause local flow phenomena to become dominant, which affect the heat and mass transport significantly. The design of these devices is therefore a non-trivial task, and the use of numerical methods is mandatory. However, the accuracy of pseudo-homogeneous reactor models, which are widely used for process simulation, rely on the knowledge of effective transport parameters, that are often unknown. In contrast, particle-resolved Computational Fluid Dynamics (CFD) has gained much popularity in the recent years, since it allows the fully spatially resolved description of the fluid dynamics and the associated transport processes, without the need of additional closure conditions. However, due to its numerical demand, this method cannot be used for full or plant scale simulations. Therefore, a combination of CFD and process simulation models is proposed, whereby the CFD results act as a provider for the effective transport parameters needed. This enhances the reliability and accuracy of process simulation tools, which is mandatory to use them for digital product design and optimization. Methods are shown and discussed that allow the reliable determination of the effective thermal conductivity, the wall heat transfer coefficient and the axial dispersion coefficient. The CFD methods are refined, making it now possible to generate packing morphologies of complex particle shapes that are very close to those found in real applications. A series of validation studies underline the accuracy that can be achieved with particle-resolved CFD. Different case studies show how particle-resolved CFD can directly be applied to investigate the intensification of transport processes in slender fixed beds. The impact of particle shape, wall design and the use of internal heat fins is studied. The results reveal a great potential of thermal process intensification in fixed-beds by the use of either macroscopic wall structures or internal heat fins.Schlanke Festbettreaktoren sind in der chemischen Industrie, insbesondere im Bereich der heterogenen Katalyse, weit verbreitet. Dieser Reaktortyp zeichnet sich durch starke Heterogenitäten in der Bettmorphologie aus, die dazu führen, dass lokale Strömungsphänomene dominant werden, die den Wärme- und Stofftransport erheblich beeinflussen. Die Auslegung dieser Apparate ist daher eine nicht-triviale Aufgabe, und der Einsatz numerischer Methoden ist zwingend erforderlich. Die Genauigkeit von pseudohomogenen Reaktormodellen, die für die Prozesssimulation weit verbreitet sind, hängt jedoch von der Kenntnis der effektiven Transportparameter ab, die oft unbekannt sind. Im Gegensatz dazu hat die partikelaufgelöste Strömungssimulation (CFD) in den letzten Jahren stark an Popularität gewonnen, da sie eine vollständig ortsaufgelöste Beschreibung der Fluiddynamik und der damit verbundenen Transportprozesse ermöglicht, ohne dass zusätzliche Schliessungsbedingungen erforderlich sind. Aufgrund des hohen numerischen Aufwands, kann diese Methode jedoch nicht für Simulationen im Anlagenmaßstab eingesetzt werden. Daher wird eine Kombination aus CFD- und Prozesssimulationsmodellen vorgeschlagen, wobei die CFD-Ergebnisse als Lieferant für die benötigten effektiven Transportparameter dienen. Dies erhöht die Zuverlässigkeit und Genauigkeit von Prozesssimulationswerkzeugen, was zwingend erforderlich ist, um sie für die digitale Produktentwicklung und -optimierung einzusetzen. Es werden Methoden gezeigt und diskutiert, die eine zuverlässige Bestimmung der effektiven Wärmeleitfähigkeit, des Wandwärmeübergangskoeffizienten und des axialen Dispersionskoeffizienten ermöglichen. Die CFD-Methoden werden verfeinert, so dass es nun möglich ist, Packungsmorphologien komplexer Partikelformen zu generieren, die denen in realen Anwendungen sehr nahe kommen. Eine Reihe von Validierungsstudien unterstreicht die Genauigkeit, die mit partikelaufgelöster CFD erreicht werden kann. Verschiedene Fallstudien zeigen, wie die partikelaufgelöste CFD direkt angewendet werden kann, um die Intensivierung von Transportprozessen in schlanken Festbetten zu untersuchen. Untersucht wird der Einfluss von Partikelform, Wanddesign und die Verwendung interner Rippen. Die Ergebnisse zeigen ein großes Potential für die thermische Prozessintensivierung in Festbetten mittels makroskopischen Wandstrukturen oder internen Rippen

Influence of Macroscopic Wall Structures on the Fluid Flow and Heat Transfer in Fixed Bed Reactors with Small Tube to Particle Diameter Ratio

Fixed bed reactors are widely used in the chemical, nuclear and process industry. Due to the solid particle arrangement and its resulting non-homogeneous radial void fraction distribution, the heat transfer of this reactor type is inhibited, especially for fixed bed reactors with a small tube to particle diameter ratio. This work shows that, based on three-dimensional particle-resolved discrete element method (DEM) computational fluid dynamics (CFD) simulations, it is possible to reduce the maldistribution of mono-dispersed spherical particles near the reactor wall by the use of macroscopic wall structures. As a result, the lateral convection is significantly increased leading to a better radial heat transfer. This is investigated for different macroscopic wall structures, different air flow rates (Reynolds number Re = 16 ...16,000) and a variation of tube to particle diameter ratios (2.8, 4.8, 6.8, 8.8). An increase of the radial velocity of up to 40%, a reduction of the thermal entry length of 66% and an overall heat transfer increase of up to 120% are found.DFG, 53182490, EXC 314: Unifying Concepts in CatalysisDFG, 414044773, Open Access Publizieren 2021 - 2022 / Technische Universität Berli

Particle-Resolved Computational Fluid Dynamics as the Basis for Thermal Process Intensification of Fixed-Bed Reactors on Multiple Scales

Process intensification of catalytic fixed-bed reactors is of vital interest and can be conducted on different length scales, ranging from the molecular scale to the pellet scale to the plant scale. Particle-resolved computational fluid dynamics (CFD) is used to characterize different reactor designs regarding optimized heat transport characteristics on the pellet scale. Packings of cylinders, Raschig rings, four-hole cylinders, and spheres were investigated regarding their impact on bed morphology, fluid dynamics, and heat transport, whereby for the latter particle shape, the influence of macroscopic wall structures on the radial heat transport was also studied. Key performance indicators such as the global heat transfer coefficient and the specific pressure drop were evaluated to compare the thermal performance of the different designs. For plant-scale intensification, effective transport parameters that are needed for simplified pseudo-homogeneous two-dimensional plug flow models were determined from the CFD results, and the accuracy of the simplified modeling approach was judged.DFG, 414044773, Open Access Publizieren 2021 - 2022 / Technische Universität Berli

Enhancing the Thermal Performance of Slender Packed Beds through Internal Heat Fins

Slender packed beds are widely used in the chemical and process industry for heterogeneous catalytic reactions in tube-bundle reactors. Under safety and reaction engineering aspects, good radial heat transfer is of outstanding importance. However, because of local wall effects, the radial heat transport in the vicinity of the reactor wall is hindered. Particle-resolved computational fluid dynamics (CFD) is used to investigate the impact of internal heat fins on the near wall radial heat transport in slender packed beds filled with spherical particles. The simulation results are validated against experimental measurements in terms of particle count and pressure drop. The simulation results show that internal heat fins increase the conductive portion of the radial heat transport close to the reactor wall, leading to an overall increased thermal performance of the system. In a wide flow range (100<Rep<1000), an increase of up to 35% in wall heat transfer coefficient and almost 90% in effective radial thermal conductivity is observed, respectively.TU Berlin, Open-Access-Mittel – 202

Enhancing the Thermal Performance of Slender Packed Beds through Internal Heat Fins

Slender packed beds are widely used in the chemical and process industry for heterogeneous catalytic reactions in tube-bundle reactors. Under safety and reaction engineering aspects, good radial heat transfer is of outstanding importance. However, because of local wall effects, the radial heat transport in the vicinity of the reactor wall is hindered. Particle-resolved computational fluid dynamics (CFD) is used to investigate the impact of internal heat fins on the near wall radial heat transport in slender packed beds filled with spherical particles. The simulation results are validated against experimental measurements in terms of particle count and pressure drop. The simulation results show that internal heat fins increase the conductive portion of the radial heat transport close to the reactor wall, leading to an overall increased thermal performance of the system. In a wide flow range (100&lt;Rep&lt;1000), an increase of up to 35% in wall heat transfer coefficient and almost 90% in effective radial thermal conductivity is observed, respectively