TY - JOUR A1 - Chairopoulou, Makrina A. A1 - Garcia-Triñanes, Pablo A1 - Teipel, Ulrich T1 - Oyster shell reuse: A particle engineering perspective for the use as emulsion stabilizers JF - Powder Technology N2 - Oyster shells are an important bioresource that causes serious environmental problems and is currently only partially repurposed. Its versatile nature is reflected in the manifold studies already proposed for the material. In this study, we add to this effort by first grinding the material with a hammer mill, beater disc mill, pin mill and wet media mill, treating part of it in a muffle furnace, noting the shift in its properties such as particle size, morphology, surface free energy, specific surface area and choosing a fraction to incorporate in a particle stabilized emulsion. The particle stabilized emulsions were prepared with oyster shells grinded by the agitated wet media mill at 2000 rpm for 30 min, with a media at x50 = 0.79 μm, a SSA at 17.16 m2/g, a SFE at 32.53 mN/m and with particles resembling a spherical shape. The emulsion was studied in terms of particle concentration, ranging from 2 to 10 wt% with the 8 wt% showing the best stability. The 8 wt% oyster shell formulation was tested and compared with a formulation using 2 wt% Aerosil particles and a surfactant store-bought product. The oyster shell particle formulation exhibited minor viscosity changes in the studied period of 8 weeks, a constant LVE range and promising behaviour in the proposed application. KW - Oyster shells Biomaterials Recycling Pickering emulsions Particle engineering Y1 - 2022 U6 - https://doi.org/10.1016/j.powtec.2022.117721 SN - 0032-5910 VL - 408 PB - Elsevier BV ER - TY - JOUR A1 - Kugler, Felix A1 - Aumüller, Jessica A1 - Krcmar, Wolfgang A1 - Teipel, Ulrich T1 - Construction and Demolition Residuals as Raw Materials for the Production of Novel Geopolymer Building Materials JF - Crystals N2 - The increasing number of new construction projects requiring high-quality building products, which, in turn, emit enormous amounts of CO2, runs counter to European and global climate goals. The increasing occupation of valuable landfill space is also an ecological problem. To meet these challenges without having to lower living standards, more ecological building materials should be used in the future. Geopolymers or alkali-activated materials, which, unlike conventional building materials, can be produced and used without a prior burning or calcination process, offer a comparatively low-CO2 alternative. Significant CO2 emissions can already be saved by using this technology. The aim of this work is to investigate whether geopolymers can also be produced from construction and demolition residuals generated by the construction industry in order to counteract the problem of the increasing use of landfill space and, at the same time, to further reduce greenhouse gas emissions in the production of building materials. For this purpose, various residual materials from the construction and demolition industry are investigated by means of XRF, XRD, and IR spectroscopy for their setting behavior by alkaline activation. At the same time, the characteristic values of compressive strength, flexural strength, bulk density, and thermal conductivity, which are important for building materials, are determined in order to test the possible applications of the resulting materials as building materials. Y1 - 2022 U6 - https://doi.org/10.3390/cryst12050678 SN - 2073-4352 VL - 12 IS - 5 PB - MDPI AG ER - TY - JOUR A1 - Kugler, Felix A1 - Fehn, Thomas A1 - Sandner, Maximilian A1 - Krcmar, Wolfgang A1 - Teipel, Ulrich T1 - Microstructural and mechanical properties of geopolymers based on brick scrap and fly ash JF - International Journal of Ceramic Engineering & Science N2 - In the present work, the influence of increasing brick scrap additions on the setting behavior and material properties of fly ash‐based geopolymers is investigated. The geopolymers produced are tested for their compressive strengths, bulk densities, and thermal conductivities, among other properties. Both the starting materials and the produced geopolymers are also investigated by infrared spectroscopy, X‐ray diffraction analysis, and scanning electron microscopy to show the relationship between the solidification behavior and the resulting material properties. The investigations show that brick scrap is very suitable as a matrix material for geopolymer production. Increasing brick scrap additions lead, among other things, to a reduction in bulk density, thermal conductivity and compressive strength. KW - geopolymers KW - mechanical properties KW - microstructure KW - waste disposal Y1 - 2022 U6 - https://doi.org/10.1002/ces2.10120 SN - 2578-3270 VL - 4 IS - 2 SP - 92 EP - 101 PB - Wiley ER - TY - JOUR A1 - Kugler, Felix A1 - Karrer, Jörg A1 - Krcmar, Wolfgang A1 - Teipel, Ulrich T1 - Setting behavior and mechanical properties of concrete rubble fly ash geopolymers JF - Open Ceramics N2 - Due to concerns about the very high primary raw material consumption and CO2 emissions of the economically important construction sector, the demand for “green” binders is growing. One option that is receiving particular attention is the material class of “geopolymers”, which could be used as a substitute for Portland cement. This new group of binders not only exhibits improved mechanical properties, but is also characterized by particularly low carbon dioxide emissions in the course of its production. This work focuses on the influence of concrete rubble on the setting behavior and microstructural properties of fly ash-based geopolymers. In the course of the investigations, the manufactured geopolymer samples are examined for the material parameters relevant to building materials, namely compressive strength, raw density and thermal conductivity. The setting behavior and the forming structures are investigated by infrared spectroscopy, X-ray diffraction analysis and scanning electron microscopy. The present work is intended to contribute to the development of a suitable recycling strategy for the material recycling of concrete rubble in novel substitute construction materials, the geopolymers. KW - Geopolymer KW - Binder KW - Concrete rubble KW - Building material KW - Circular economy KW - CO2-Reduction Y1 - 2022 U6 - https://doi.org/10.1016/j.oceram.2022.100286 SN - 2666-5395 VL - 11 PB - Elsevier BV ER - TY - JOUR A1 - Teipel, Ulrich T1 - New separation function for the stationary screening process JF - The Canadian Journal of Chemical Engineering N2 - AbstractIn the present study, a new separation function T(x,α’,β) for the steady‐state screening process is presented. This new grade efficiency T(x,α’,β) presented here is a function of particle size x, separation sharpness α’, and the newly introduced separation efficiency β. With this new efficiency function, the screening classification process can be described exactly. Especially in the fine and coarse material ranges, a very good correlation of the calculated function with the measured values can be observed. A comparison of the grade efficiency function with separation sharpness α’, separation efficiency β, and only with the measure for separation efficiency has shown that the new grade efficiency T(x,α’,β) allows a significant improvement in the characterization of the stationary screen classification process. When compared with other models, the new model of the grade efficiency T(x,α’,β) shows a significantly higher correlation with the measured values and is therefore very well suited to describe a grade efficiency for the stationary screening process. Y1 - 2022 U6 - https://doi.org/10.1002/cjce.24416 SN - 0008-4034 VL - 100 IS - 9 SP - 2347 EP - 2354 PB - Wiley ER - TY - JOUR A1 - Chairopoulou, Makrina A. A1 - Kokkinos, Nikolaos A1 - Garcia-Triñanes, Pablo A1 - Mitropoulos, Athanassios C. A1 - Teipel, Ulrich T1 - Evaluation of particle recovery from microalgae JF - Advanced Powder Technology N2 - Coccoliths are micro-structured biomineral particles found in cell protective covering layers of coccolithophore species. They are mainly composed of CaCO3 and their individual crystal entities are arranged in such a way that they construct complex and unique structures. This complexity is found down to the individual particle level and appears to have promising properties to offer. This study focuses on the essential step prior to any kind of implementation, which is the recovery of the material. It summarizes cleaning protocols found in literature, compares them for the first time for the same freshly cultivated material and addresses challenges that still need to be overcome. Further, it highlight the advantages and disadvantages of the best cleaning protocols, suggests optimizations with promising results and uses size distribution measurements to analyse the recovery efficiency. To that end, further characterization techniques, new for coccoliths, are introduced and used to improve our current knowledge of the particles behaviour. KW - Coccoliths Particle recovery Microalgae Emiliania huxleyi Biomaterials Y1 - 2021 U6 - https://doi.org/10.1016/j.apt.2021.06.013 SN - 0921-8831 VL - 32 IS - 8 SP - 3023 EP - 3033 PB - Elsevier BV ER - TY - JOUR A1 - Eisenlauer, Moritz A1 - Teipel, Ulrich T1 - Comminution energy and particulate properties of cutting and hammer-milled beech, oak, and spruce wood JF - Powder Technology N2 - As a result of the development of innovative technologies for use of renewable materials, these materials are increasingly used for the production of precursors and basic chemicals for the chemical industry. The upstream process of comminution is a key element in the use of renewable raw materials, which impacts the consecutive disintegration of the materials, which means the separation of the three main components cellulose, hemicellulose and lignin as well as the handling. Energy efficiency of the comminution process is of utmost importance to make renewable resources more competitive with petrochemical products. The key parameters to increased energy efficiency are, besides the mill type and the mill operation parameters, the species of the renewable resource, in terms of moisture content and the mechanical properties. A better understanding of these interdependencies can help to improve the adjustment of particle size distribution and particle shape as well as the energy demand for the comminution process, which impacts the overall efficiency of the supply chain process, disintegration as well as the conversion. This work focuses on the comminution of lignocellulosic biomass in a cutting mill and a hammer mill and how the specific comminution energy and particulate properties are affected by the type of mill, the species of wood, the archived size reduction as well as the moisture content. Therefore two spices of hardwood, common beech (F. sylvatica L.) and oak (Q. robur L.), and one species of coniferous wood common, spruce (P. abies L.), where comminuted under variation of different process parameters. The specific comminution energies were determined and the comminution products were characterized by dynamic image analysis. This work describes the influence of the process parameters, internal classifying screen, type of stress and moisture content, on the comminution products and the specific comminution energy. From the results of the experiments, functions were determined which can describe the influence of the type of mill, the moisture content, the type of wood and the comminution ratio on the specific comminution energy. KW - Wood Specific comminution energy Particulate properties Hammer mill Cutting mill Y1 - 2021 U6 - https://doi.org/10.1016/j.powtec.2021.03.072 SN - 0032-5910 VL - 394 SP - 685 EP - 704 PB - Elsevier BV ER - TY - JOUR A1 - Chairopoulou, Makrina A. A1 - Kratzer, Fabian A1 - Groß, Roland A1 - Herrmann, Michael A1 - Teipel, Ulrich T1 - Influence of the Temperature on Coccolith‐Containing Systems from Emiliania huxleyi Cultivations JF - Chemical Engineering & Technology N2 - Thermogravimetric analysis of a coccolith‐containing biogenic broth showed a three‐step degradation process. According to this system behavior, the biogenic broth was heated to specific temperatures and characterized in terms of its morphology, surface chemistry, and crystallinity. The elemental and organic composition of the treated samples was also evaluated and compared to the reference material. The presented results were acquired in an effort to exploit pretreatment scenarios for such a biogenic system that would improve and support a separation process. Y1 - 2020 U6 - https://doi.org/10.1002/ceat.201900507 SN - 0930-7516 VL - 43 IS - 5 SP - 904 EP - 912 PB - Wiley ER - TY - JOUR A1 - Dresel, Alexander A1 - Teipel, Ulrich T1 - Jet Dispersion of Multiwall Carbon Nanotubes and Correlation with Suspension Rheology JF - Chemical Engineering & Technology N2 - A novel jet dispersion technique was developed and investigated which enabled excellent carbon nanotube (CNT) dispersion by high exfoliation at even very low pressure drops. Suitable procedures were developed for the characterization of agglomerate size and fraction of individual CNTs. The appropriate characterization enabled the definition of a dimensionless dispersing parameter and the development of a kinetic model that describes CNT dispersion in dependence of the volumetric energy input. The rheological behavior of CNT suspensions in steady‐shear flows was investigated and demonstrated how the agglomerate fracture and CNT individualization influence the suspension viscosity. Y1 - 2020 U6 - https://doi.org/10.1002/ceat.201900534 SN - 0930-7516 VL - 43 IS - 5 SP - 869 EP - 878 PB - Wiley ER - TY - JOUR A1 - Eisenlauer, Moritz A1 - Teipel, Ulrich T1 - Comminution of Wood – Influence of Process Parameters JF - Chemical Engineering & Technology N2 - An essential element for sustainable use of renewable resources is an efficient comminution process for which the relation between energy input and size reduction is of great importance. Fine comminution of beech, oak, and spruce wood chips in cutting and hammer mills at different moisture content levels is investigated. The influence of the different process parameters as well as the size reduction performed by the hammer and cutting mill on the specific comminution energy is reported and the particulate properties of the comminution products are reported. Considering the energy requirements, functional relations were derived from the experimental results, which describe the relation between comminution energy and size reduction. Y1 - 2020 U6 - https://doi.org/10.1002/ceat.201900488 SN - 0930-7516 VL - 43 IS - 5 SP - 838 EP - 847 PB - Wiley ER - TY - JOUR A1 - Teipel, Ulrich A1 - Wolf, Sebastian A1 - Schreiber, Alex T1 - Durchgangswiderstand von partikulären Systemen JF - Chemie Ingenieur Technik N2 - Die elektrischen Eigenschaften von Partikeln insbesondere der Durchgangswiderstand von Partikelschüttungen haben in vielen verfahrenstechnischen Prozessen, bei der Produktqualifizierung oder dem Brand‐ und Explosionsschutz eine entscheidende Bedeutung. Da sich der Ladungstransport in einem dispersen System von dem in einem homogenen Festkörper unterscheidet, ist der Durchgangswiderstand entscheidend von den Produkteigenschaften der Partikel und des Fluids abhängig. Im Rahmen dieser Arbeit wurde die Abhängigkeit des Durchgangswiderstandes von der inneren Struktur der Schüttung, der relativen Feuchtigkeit, der Konditionierungszeit bei unterschiedlichem Klima und der mittleren Partikelgröße in einer konzentrischen Messzelle untersucht. T2 - Electrostatic Resistance of Particulate Systems Y1 - 2020 U6 - https://doi.org/10.1002/cite.201800141 SN - 0009-286X VL - 92 IS - 3 SP - 229 EP - 237 PB - Wiley ER - TY - JOUR A1 - Gundermann, Michael A1 - Raab, Florian A1 - Raab, Daniel A1 - Botsch, Tilman T1 - Investigation of the heat transfer coefficient during the condensation of small quantities of water vapour from a mixture with a high proportion of non-condensable gas in a horizontal smooth tube JF - International Journal of Heat and Mass Transfer N2 - During heat recovery of exhaust gas energy in a shell and tube heat exchanger, the exhaust gas is cooled down and the water vapour content may condense when the corresponding temperature is reached. In this case, a condensation heat exchanger allows recovering the latent heat in addition to the sensible heat and is therefore beneficial for a preferably high heat recovery. The database and algorithms for the design of this kind of apparatus are still nowadays quite week because only little experimental work is realized with condensation of water vapour from a mixture with a very high proportion of non-condensable gas in horizontal tubes. The actual research work improves this database with a considerable amount of experimental data and proposes a correlation for the prediction of the heat transfer coefficient in an exhaust gas heat exchanger in which parts of the gas humidity condense. All experiments were carried out under conditions, which are typical for this kind of heat exchangers, hence the presented results can be used for the design of condensation heat exchangers in industrial heat transfer systems. A gas inlet temperature of 120 °C, a range of the air-steam mixture Reynolds number 11,000 Re 31,000, three tube lengths between 1.87 m and 3.04 m, water vapour volume fractions of 7 % to 14.5 % as well as tube diameters of 22 mm and 28 mm were selected to derive the correlation. Furthermore, additional tube lengths (0.574 m, 0.973 m, 1.373 m) were investigated to determine the parameters influencing the condensation rate and comprehensive location profiles over the tube length. A correlation for a correction factor is derived, which enables to calculate the increase of the heat transfer coefficient due to condensation from the dry heat transfer coefficient without condensation. This dry heat transfer coefficient is calculated by the measured values in the inlet and outlet for a purely dry air-steam mixture cooling without condensation. The correction factor depend on the water vapour volume fraction, the Reynolds number and the geometry ratio between the inner diameter and the tube length. KW - Condensation ; Non-condensable gas ; Heat transfer correlation ; Inside horizontal tube ; Heat exchangers ; Flue gas Y1 - 2021 U6 - https://doi.org/10.1016/j.ijheatmasstransfer.2021.121016 SN - 0017-9310 VL - 170 PB - Elsevier BV ER - TY - CHAP A1 - Weers, Martin A1 - Wollmann, Annett A1 - Teipel, Ulrich A1 - Weber, Alfred P. T1 - Dynamics of Separation Characteristics of Sieving and Flow Classification Processes T2 - Dynamic Flowsheet Simulation of Solids Processes Y1 - 2020 SN - 9783030451677 U6 - https://doi.org/10.1007/978-3-030-45168-4_10 SP - 349 EP - 390 PB - Springer International Publishing CY - Cham ER - TY - CHAP A1 - Raufeisen, A. A1 - Breuer, M. A1 - Kumar, V. A1 - Botsch, Tilman A1 - Durst, F. T1 - LES and DNS of Melt Flow and Heat Transfer in Czochralski Crystal Growth T2 - High Performance Computing in Science and Engineering ’06 N2 - In the present work, computations of flow and heat transfer in an idealized cylindrical Czochralski configuration are conducted using Large Eddy Simulation (LES) with the flow solver FASTEST-3D developed at LSTM Erlangen. The results match well with DNS data from the literature. However, detailed data for analysis of turbulent quantities are not available. Therefore, DNS computations are conducted using the code LɛSOCC, employing explicit time marching. Preliminary simulations show the high efficiency of the solver on the NEC SX-8. Furthermore, from a study of the velocity profiles at the wall, the resolution requirements had to be corrected such that the computational grid will now consist of approximately 8 × 106 control volumes. The present run of the DNS took more than 540 hours of walltime on 8 processors. With the results, the LES computations will be thoroughly validated so that appropriate models and parameters can be chosen for efficient and accurate simulations of practically relevant cases. Y1 - 2007 SN - 9783540361657 U6 - https://doi.org/10.1007/978-3-540-36183-1_20 SP - 279 EP - 291 PB - Springer CY - Berlin, Heidelberg ER - TY - CHAP A1 - Raufeisen, A. A1 - Botsch, Tilman A1 - Kumar, V. A1 - Breuer, M. A1 - Durst, F. T1 - Prediction of Flow and Heat Transfer in a Czochralski Crucible using LES with Interface Tracking T2 - Springer Proceedings in Physics Y1 - 2007 SN - 9783540326021 U6 - https://doi.org/10.1007/978-3-540-32603-8_59 SP - 289 EP - 292 PB - Springer CY - Berlin, Heidelberg ER - TY - GEN A1 - Neumeister, Roberta Fatima A1 - Reichel, Christoph A1 - Prisco Petry, Adriane A1 - Viçosa Möller, Sergio T1 - NUMERICAL ANALYSIS OF FLOW INTERACTIONS WITHIN A BANK OF TUBES WITH CLOSE SPACE RATIO T2 - FIV-2024-0052, FIV2024; FSI & FIV + N 10th Symposium on Fluid-Structure Interactions, Flow-sound Interactions, Flow-Induced Vibration & Noise N2 - The flow within a tube bank is characterized by multiple concurrent interaction mechanisms, contributing to a complex response. To gain a better understanding of these mechanisms, it can be helpful to simplify the problem by focusing on fixed rows to apply the free-to-vibrate approach later. This study conducts a numerical analysis of the fundamental characteristics of crossflow in five rows of stationary cylinders. Our goal is to establish a connection between the variations in velocity fields, the forces acting on the cylinders, and the expected vibration response. Simulations of cylinder rows were executed within a domain featuring a cross-section of 0.193 m x 0.146 m and a length of 0.8 m. The cylinders, with an external diameter of 25 mm, were placed with a longitudinal and transverse spatial ratio of 1.26. The governing equations, including continuity and Navier-Stokes equations, were solved using Large Eddy Simulation with the Smagorinski-Lilly subgrid model, employing dynamic stress modeling within Ansys Fluent 19. The Reynolds number was set at 8.4 x 10^3, based on the gap flow velocity and the diameter of a single cylinder. The results from the transient field indicate interactions between the gap flow and the cylinders following literature experimental visualizations and numerical simulations. Variations in velocity within the gaps between the cylinders highlight the dynamic redistribution of flow. This flow pattern significantly influences the forces acting on the cylinders, demonstrating an increase in force coefficients at specific cylinder positions. The sudden increase in the lift force in one of the cylinders can be the main factor related to the fluid-elastic instability occurrence. KW - numerical analysis, crossflow, tube bank, velocity fields. Y1 - 2024 ER - TY - RPRT A1 - Reichel, Christoph A1 - Reichel, Philip T1 - Simulation of Tube Bundle Vibrations with CFX10 BT - Mendeley Data, V1, CFX User Fortran subroutines for the simulation of tube bundle vibrations N2 - For the work documented in https://mediatum.ub.tum.de/doc/601988/file.pdf (or alternatively in https://www.researchgate.net publication/36418211_Numerische_Simulation_fluidinduzierter_Rohrbundelschwingungen#fullTextFileContent) and DOI: 10.1115/PVP2009-77530 on the simulation of tube and tube bundle vibrations CFX User Fortran subroutines were created and used. A small/short documentation (hand written pdf) has been added to the Fortran Code. The Code is uploaded here. An application example with CFX ccl.files and CFX-runs (def, out, res ...) is added in another zip-file. The code and CFX ccl will not run with actual versions of CFX. It was running with CFX 5.7.1 and with CFX 10. PGI (Portland Group) Fortran Compiler had to be used, because of file input and output operations. We approached ANSYS to transform to newer versions of CFX (and probably Intel OneAPI Fortran). If successful, we also plan to provide the transformed code. KW - Computer Simulation, Vortex Induced Vibration Y1 - 2024 PB - Mendeley Data ER - TY - JOUR A1 - Nöske, Markus A1 - Müller, Jannes A1 - Nowak, Christine A1 - Li, Kangqi A1 - Xu, Xiaolu A1 - Breitung-Faes, Sandra A1 - Kwade, Arno T1 - Multicomponent Comminution within a Stirred Media Mill and Its Application for Processing a Lithium-Ion Battery Slurry JF - Processes N2 - This study presents an approach for targeted comminution of component mixtures within a wet-operated stirred media mill. In the first step, a general understanding of the interactions between individual components on the grinding result with mixtures could be gained with basic experiments and following our former research work. In particular, a protective effect of the coarser particles on the fines could be elucidated. These findings were used to develop a process for the production of a battery slurry containing fine ground silicon particles as well as dispersed carbon black and graphite particles. By a tailored sample preparation applying a combination of particle dissolution and separation, the particle size distributions of carbon black and graphite particles were analyzed separately within the produced battery slurries. Based on the selective particle size analysis, the slurry preparation could be transferred from a complex multistage batch process using a dissolver to a stirred media mill, which was finally operated in a continuous one-passage mode. The prepared slurries were subsequently further processed to silicon-rich anodes using a pilot scale coating and drying plant. Afterward, the produced anodes were electrochemically characterized in full cells. The cell results prove a comparable electrochemical behavior of anode coatings derived from a dissolver- or mill-based slurry production process. Therefore, we could demonstrate that it is possible to integrate the mixing process for the production of multicomponent slurries into the comminution process for the preparation of individual materials upstream. Even with nearly identical starting sizes of their feed materials, the targeted particle size distributions of the single components can be reached, taking into account the different material-dependent particle strengths and sequential addition of single components to the multicomponent comminution process. KW - multicomponent comminution KW - stirred media mill KW - battery slurry KW - silicon anode Y1 - 2022 U6 - https://doi.org/10.3390/pr10112309 SN - 2227-9717 VL - 10 IS - 11 PB - MDPI AG ER - TY - JOUR A1 - Miethke, Lina A1 - Prziwara, Paul A1 - Finke, Jan Henrik A1 - Breitung-Faes, Sandra T1 - Opposing Effects of Additives in Dry Milling and Tableting of Organic Particles JF - Pharmaceutics N2 - Applying additives and excipients during the dry processing of fine particles is a common measure to control the particle–particle interactions, to specifically influence the powder properties and to enhance the process efficiency or product quality. In this study, the impacts of a particulate lubricant, a nano-disperse flow additive and liquid grinding aids on the dry fine milling and subsequent tableting of the ground material were investigated for three different organic model compounds. It is presented that the three additive classes cause varying and partly opposing effects during these process steps. Especially the lubricant and the grinding aids were shown to increase the efficiency of the milling process as well as the product fineness of the ground material, and to avoid critical product adhesions on the machine surfaces. Thereby, stable and efficient grinding conditions were partially not possible without the addition of such additives. However, as these positive effects are attributed to a reduction of the adhesive forces between the particles, much lower tablet strengths were achieved for these additives. This propagation of powder, and in turn, final product properties over whole process chains, has not been studied in detail so far. It was further revealed that the material behavior and the microstructure of the product particles is decisive for the processing as well, which is why additive effects may be product-specific and can even be suppressed under certain processing conditions. In comparison to the process performances, the powder properties and surface energies of the product particles were less influenced by the additives. On the contrary, particle-based morphologies or deformation behavior seem to play a major role in comparison to inorganic materials. Thus, it can be stated that global bulk properties and surface energies provide first indications of powder behavior and susceptibility. However, additional specific properties need to be evaluated to more clearly understand the influences of additives. KW - organic particles KW - additives KW - dry milling KW - tableting KW - compaction KW - lubricants KW - flow aids KW - grinding aids Y1 - 2021 U6 - https://doi.org/10.3390/pharmaceutics13091434 SN - 1999-4923 VL - 13 IS - 9 PB - MDPI AG ER - TY - JOUR A1 - Botsch, T. W. A1 - Stumpmeier, S. A1 - Ganser, J. T1 - Simulation of the transient condensation process in steam pipes during start up of a steam power plant JF - Heat and Mass Transfer N2 - This paper introduces a model predicting the unsteady conditions in vertical pipes of a steam power station during start up of the plant. Knowing the time depending variation in the rate of condensation in the pipe is helpful for optimizing the design of the drainage system, which removes the condensate collected from the pipes. At present this system is designed on the basis of the total amount of condensate produced in a particular pipe during start up of the power plant. The model presented will provide a design based on the true maximum flow rate during said period. The paper describes the mass and energy balances for the gas and the condensate as well as the energy balance for the wall. All equations are transformed into a set of differential and algebraic equations and solved at once. The model was subsequently applied on genuine industrial scenarios. The results obtained from the model are discussed in detail and compared with experimental data. In all situations considered, the maximum condensate flow rate calculated was less than 50% of the estimated value using standard design methods. Y1 - 2010 U6 - https://doi.org/10.1007/s00231-010-0714-3 SN - 0947-7411 VL - 46 IS - 10 SP - 1187 EP - 1197 PB - Springer Science and Business Media LLC ER - TY - CHAP A1 - Neumeister, Roberta Fatima A1 - Reichel, Christoph A1 - Prisco Petry, Adriane A1 - Möller, Sergio Viçosa T1 - Numerical analysis of crossflow over one and two rows of cylinders T2 - Proceedings of the 27th International Congress of Mechanical Engineering N2 - The flow inside a bank of tubes is complex and presents several interaction mechanisms acting at the same time in different positions of the equipment. Simplifying the structures to two cylinders or a few rows can be a way to understand part of the mechanisms and then extrapolate them to a bank of tubes. The flow over a single row in closed space presents wide and narrow wakes, similar to the structure observed in two cylinders side by side, these structures interacting with a second row show a significant change in the incoming flow parameters. The present study aims to show a numerical analysis of the main characteristics of the crossflow in one and two rows of fixed cylinders and to relate the changes in the pressure fields and forces in the cylinders to the expected vibration response. Simulations of rows of cylinders were performed in a domain with a cross-section of 0.193 x 0.05 m and a length of 0.8 m. Five and ten cylinders with an external diameter of 25 mm were applied. The longitudinal and transverse spatial ratio is 1.26 and all cylinders were fixed. The continuity and Navier-Stokes equations were solved using the Large Eddy Simulation with the Smagorinski-Lilly subgrid model with dynamic stress in Ansys Fluent 19. The Reynolds number is 5 x 10^4, based on the gap flow velocity and the diameter of a single cylinder. The transient analysis is performed with a time step of 1 x10^-5 s and the 10^-6 convergence criterion is used for all monitored variables. Preliminary results show wake asymmetry after the first and second rows of cylinders. There is an asymmetry between the velocity in the gaps between the cylinders indicating a redistribution of the flow, increasing and decreasing the velocity in the gaps between the cylinders. This velocity and pressure distribution influences the forces along the cylinders showing an increase in forces coefficients at some cylinder positions. The non-homogeneous distribution of velocity in the gaps is an important factor in determining the vibrational response, as the models use this information as an input parameter to determine the instability limits. KW - numerical analysis, crossflow, row of cylinders, flow-induced vibration Y1 - 2023 U6 - https://doi.org/10.26678/ABCM.COBEM2023.COB2023-0404 PB - ABCM ER - TY - JOUR A1 - Sterling, David A1 - Breitung-Faes, Sandra A1 - Kwade, Arno T1 - Improved energy transfer model for mechanistic scale-up of stirred media mills JF - Powder Technology N2 - Wet-operated stirred media mills are commonly used in the field of fine and ultra-fine grinding. Depending on the application, there are different mill geometries, sizes and mill equipment materials of which the grinding chamber lining and the stirrer are made. Increasing energy prices demand an energy-efficient mill operation for a desired product, which can be achieved with mechanistic stress models. Here, besides the mill geometry and volume, the process parameters and various energy-transfer-coefficients are of importance. In this work, the impact of different mill equipment materials affecting the mill-related-energy-transfer-coefficients on performance prediction and scale-up using the advanced stress model are investigated. It was found that the mill-related-energy-transfer-coefficients as well as the improved grinding-media-energy-transfer-coefficients have a significant effect on the prediction precision of the comminution times and specific energies for chosen target particle sizes. KW - Stirred media mill KW - Scale up KW - Mechanistic model KW - Mill equipment materials KW - Advanced stress model KW - Energy transfer coefficient KW - Energy efficiency Y1 - 2024 U6 - https://doi.org/10.1016/j.powtec.2024.119978 SN - 0032-5910 VL - 444 PB - Elsevier BV ER - TY - JOUR A1 - Peppersack, Christoph A1 - Flach, Frederik A1 - Prziwara, Paul A1 - Damm, Cornelia A1 - Breitung-Faes, Sandra A1 - Peukert, Wolfgang A1 - Kwade, Arno T1 - Conceptual stabilizer selection for nanomilling based on dispersibility parameters JF - Advanced Powder Technology N2 - The choice of stabilizers to prevent particle agglomeration during nanomilling is an elaborate process which is often based on empirical rules and experience. Usually, extensive screening studies are required to find an appropriate stabilizing additive. The present study shows how the selection of polymeric stabilizers can be narrowed down to a couple of additives based on Hansen solubility parameters. The stabilizing capability was found to be a function of the difference between solubility parameters of additive and particulate species. Solubility parameters of different additives and two particle species were determined by inverse gas chromatography and the stabilization performance was evaluated by nanomilling experiments conducted with a stirred media mill. It is shown that a certain difference of solubility parameters between particle and additive is necessary in order to provide colloidal stability of small particles after milling. On the one hand, the additive needs a certain affinity to the particle surface, while on the other hand it also has to be compatible with the solvent. Based on experimental data, a solubility parameter difference in the range of 7.5–10 MPa0.5 was identified as a good measure for a proper stabilizer selection. The approach was proved for two organic particle species and represents a promising tool for a more efficient formulation development of drug nanosuspensions. KW - Nanomilling KW - Colloidal stability KW - Hansen solubility parameter KW - Inverse gas chromatography Y1 - 2023 U6 - https://doi.org/10.1016/j.apt.2023.104197 SN - 0921-8831 VL - 34 IS - 10 PB - Elsevier BV ER - TY - JOUR A1 - Peppersack, Christoph A1 - Kwade, Arno A1 - Breitung-Faes, Sandra T1 - Selective particle size analysis in binary submicron particle mixtures using density dependent differential sedimentation JF - Advanced Powder Technology N2 - Particle size characterization of heterogeneous mixtures is a challenging task, as it is not feasible to assign the measured signals to the individual components. Within this framework, the study proposes a method that applies the working principle of differential centrifugal sedimentation (DCS) in order to simultaneously separate and measure the denser component within a binary material mixture of submicron particles. The method was validated using a model system consisting of polyvinyl chloride (PVC) and diamond particles in a size range of 0.5 – 1.5 µm. The results proved that by applying a proper density gradient fluid, the diamond particles can be selectively analyzed by hindering the sedimentation of the lighter PVC component. Furthermore, a very promising application could be found with respect to wet fine grinding processes in stirred media mills. In fact, the approach was utilized to individually determine the particle size distribution of the grinding media wear within an ultrafine organic product. Despite the low quantity of wear particles, it was possible to separate them from the organic product under appropriate density conditions. The size distributions of both the wear and the product particles were validated with SEM images, confirming the feasibility of the method. KW - Grinding media wear KW - Differential centrifugal sedimentation KW - Selective particle size analysis KW - Heterogeneous mixtures KW - Stirred media milling Y1 - 2021 U6 - https://doi.org/10.1016/j.apt.2021.09.010 SN - 0921-8831 VL - 32 IS - 11 SP - 4049 EP - 4057 PB - Elsevier BV ER - TY - JOUR A1 - Sterling, David A1 - Breitung-Faes, Sandra A1 - Kwade, Arno T1 - Experimental evaluation of the energy transfer within wet operated stirred media mills JF - Powder Technology N2 - Wet-operated stirred media mills are commonly used in the field of fine and ultra-fine grinding. Depending on the application, there are different mill geometries and mill equipment materials of which the grinding chamber lining and the stirrer are made. Polyurethane and ceramics are frequently implemented materials. Besides the process-relevant effects such as cooling and wear prevention, an energy efficient mill operation is intended, which can be achieved, by using mechanistic stress models. Here, besides the mill geometry, the process parameters, various energy-transfer-coefficients are also determined. In this work, the effect of different mill equipment materials on the mill-related-energy-transfer-coefficient are investigated by experiments while operating different mills only with water and grinding media but without feed material. It was found that the mill equipment material has a significant effect on the power consumption and thus, the energy transfer within the mill as a result of friction between different materials. KW - Stirred media mill KW - Grinding chamber and stirrer materials KW - Advanced stress model KW - Energy transfer coefficient KW - Energy efficiency Y1 - 2023 U6 - https://doi.org/10.1016/j.powtec.2023.118579 SN - 0032-5910 VL - 425 PB - Elsevier BV ER - TY - JOUR A1 - Peppersack, Christoph A1 - Wermbter, Karsten A1 - Kwade, Arno A1 - Garnweitner, Georg A1 - Breitung-Faes, Sandra T1 - Top-Down Formulation of Goethite Nanosuspensions for the Production of Transparent, Inorganic Glass Coatings JF - Coatings N2 - This study presents a simple but effective process route for the production of transparent coatings on glass substrates from inorganic pigment goethite. For this purpose, coating suspensions were prepared by wet milling with a stirred media mill. A water/ethanol mixture was used as the liquid medium to take advantage of the resulting low surface tension for the coating process. In this manner, stable suspensions with particles of down to 50 nm in size were obtained, which already showed a significant increase in transparency. With regard to grinding characteristics, particularly low stress energies proved to be energetically reasonable. The coating step was performed by wet film deposition, achieving coating thicknesses in a range of 0.5–2.5 µm via dip coating. Highly transparent coatings were obtained by applying small particles of 50 nm, which exhibited a significantly lower scattering loss of light (≈3%) in comparison to particles of around 300 nm (70–80%). Additionally, the film color could be adjusted through a variation of the drying temperature due to a conversion of goethite to hematite by dehydration. Since transparency was not affected, this provides an easy-to-implement process adaptation for controlling coating colors. KW - goethite KW - stirred media milling KW - top-down formulation KW - transparent coating KW - dip coating Y1 - 2022 U6 - https://doi.org/10.3390/coatings12030330 SN - 2079-6412 VL - 12 IS - 3 PB - MDPI AG ER - TY - JOUR A1 - Sterling, David A1 - Schons, Didier A1 - Breitung-Faes, Sandra A1 - Kwade, Arno T1 - Effects of axial grinding media distribution on the disc wear behavior of a stirred media mill JF - Minerals Engineering N2 - Stirred media mills are commonly used process units for wet fine grinding and dispersing. During operation the grinding media and the feed material can cause wear to the process units of the stirred media mill. One typical representative of horizontal stirred media mills is the IsaMillTM, in which an internal classifier diverts the grinding media away from the discharge and implies a counteracting current force to the drag forces caused by the suspension flow. In this work, the disc wear of a pilot scale horizontal mill was investigated with regard to the axial grinding media distribution and other process parameters. In order to create quickly and well visible disc wear patterns, manufactured aluminum discs instead of the original polyurethane discs were specially used. For each set of operating parameters, a separate new pair of discs was installed. A radiometric densitometer was installed to measure the axial grinding media filling degree lengthwise to the M4 IsaMillTM. This method allows the determination of the local filling degree by correlation of the attenuation of gamma radiation from a Cs137 nuclide. The experiments showed that the disc wear per energy input increases with rising stress energy. With respect to the axial grinding media distribution, higher wear rates were observed in areas of increased grinding media filling ratios. As a result, it can be stated that the wear is a function of the local grinding media distribution and of the stress energy. In zones with a higher local grinding media filling degree, an increased disc wear is evident. Consequently, mills on a production scale could theoretically realize longer plant operating times and lower maintenance costs by securing a more homogeneous grinding media distribution. KW - Disc and stirrer wear KW - Stirred media mill KW - Axial grinding media filling degree KW - Radiometric density measurement Y1 - 2022 U6 - https://doi.org/10.1016/j.mineng.2022.107702 SN - 0892-6875 VL - 185 PB - Elsevier BV ER - TY - JOUR A1 - Cai, Yingying A1 - Peng, Wentao A1 - Song, Qingyuan A1 - Pluta, Denis A1 - Peppersack, Christoph A1 - Breitung-Faes, Sandra A1 - Kwade, Arno A1 - Bigall, Nadja C. A1 - Vana, Philipp T1 - Nanoengineering of Egyptian Blue Nanosheets: Advantages and Limitations for Near-Infrared Photoluminescence Applications JF - ACS Applied Optical Materials N2 - The ancient inorganic pigment Egyptian Blue is a fluorophore with outstanding near-infrared (NIR) performance and is thus considered as an emerging optical material that meets the current demand for cheap, efficient, and nontoxic NIR nanofluorophores. Herein, we present a protocol for the quick mass production of Egyptian Blue (CaCuSi4O10) nanosheets (EBNSs) with lateral size down to ∼100 nm by applying state-of-the-art ball-milling techniques. A systematic decay of the NIR photoluminescence behavior with decreasing size of the EBNSs was found, which challenges the desired application of EBNSs as bioimaging markers and other nanoapplications. To pave the way to surface modifications of EBNSs, we deposited a thin layer of silica on the surface of the EBNSs. Taking advantage of this modification, we subsequently performed surface-initiated reversible addition–fragmentation chain transfer (RAFT) polymerization in order to grow both hydrophilic and hydrophobic polymer brushes from EBNSs, which enhanced dispersibility of the nanosheets and even delivered function. By matching the refractive index of the EBNS with its polymer shell, the quality of the NIR photoluminescence of the EBNS could significantly be improved, since disturbing light scattering at the interface could effectively be suppressed. Our results provide a clear picture of the advantages and limitations of EBNSs as optical nanomaterials for NIR fluorescence applications. KW - cuprorivaite KW - NIR fluorophore KW - NIR photoluminescence KW - nanocomposite KW - Layered silicate KW - surface modification KW - surface-initiated polymerization KW - silica coating Y1 - 2022 U6 - https://doi.org/10.1021/acsaom.2c00114 SN - 2771-9855 VL - 1 IS - 1 SP - 465 EP - 472 PB - American Chemical Society (ACS) ER - TY - JOUR A1 - Kwade, Arno A1 - Möller, Marcel A1 - Müller, Jannes A1 - Hesselbach, Jutta A1 - Zellmer, Sabrina A1 - Doose, Stefan A1 - Mayer, Julian A1 - Michalowski, Peter A1 - Powell, Malcolm A1 - Breitung-Faes, Sandra T1 - Comminution and Classification as Important Process Steps for the Circular Production of Lithium Batteries JF - KONA Powder and Particle Journal N2 - Lithium-ion batteries (LIBs) provide the largest source of electrical energy storage today. This paper covers the use of comminution processes and, thus, crushers and mills for particle breakage and dispersing, as well as classifiers for particle separation within the process chain, from the raw material to the final lithium battery cell and its recycling at end of life. First of all, the raw materials for the active material production have to be produced either by processing primary raw materials, or by recycling the spent lithium batteries. The end-of-life battery cells have to be shredded, the materials separated and then milled in order to achieve the so-called black mass, which provides a secondary material source with very valuable components. Using these materials for the synthesis of the cathode active materials, milling has to be applied in different stages. The natural graphite, increasingly used as anode material, has to be designed in mills and classifiers for achieving targeted properties. Nanosized silicon is produced by nanomilling using stirred media mills as a primary option. Conductive additives for LIBs, like carbon black, have to be dispersed in a solvent with machines like planetary mixers, extruders or stirred media mills. In the future, mechanochemical synthesis of solid electrolytes will especially require additional application of comminution processes. KW - graphite KW - silicon KW - battery recycling KW - active material synthesis KW - solid state batteries KW - electrode production Y1 - 2023 U6 - https://doi.org/10.14356/kona.2023006 SN - 0288-4534 VL - 40 IS - 0 SP - 50 EP - 73 PB - Hosokawa Powder Technology Foundation ER - TY - JOUR A1 - Raufeisen, A. A1 - Breuer, Michael A1 - Botsch, T. A1 - Delgado, A. T1 - Prediction of the three-phase boundary movement in Czochralski crystal growth JF - Journal of Crystal Growth N2 - A numerical algorithm is presented which allows three-dimensional time-dependent simulations of Czochralski and other crystal growth processes. Besides the computation of turbulent flow and heat transfer in the melt, it includes the movement of the crystallization interface between melt and crystal, the dynamics of the melt free surface with the meniscus and the variation of the three-phase boundary. Thus, there is the potential that crystal diameter variations, which occur during growth of the start and the end cone can be predicted. This is illustrated by results of sample computations. Y1 - 2010 U6 - https://doi.org/10.1016/j.jcrysgro.2010.05.009 SN - 0022-0248 VL - 312 IS - 16/17 SP - 2297 EP - 2299 PB - Elsevier BV ER - TY - JOUR A1 - Lemouedda, A. A1 - Breuer, Michael A1 - Franz, E. A1 - Botsch, T. A1 - Delgado, A. T1 - Optimization of the angle of attack of delta-winglet vortex generators in a plate-fin-and-tube heat exchanger JF - International Journal of Heat and Mass Transfer N2 - Delta-winglet vortex generators (VGs) are known to enhance the heat transfer between the energy-carrying fluid and the heat transfer surfaces in plate-fin-and-tube banks. In this study optimal angles of attack of the delta-winglets are investigated based on the Pareto optimal strategy. The optimization process combines a CFD analysis, genetic algorithms and the response surface methodology. The angle of attack of a pair a delta-winglet-type VGs mounted behind each tube is varied between β = −90° and +90°. Three circular tube rows with inline and staggered tube arrangements are investigated for Reynolds numbers from 200 to 1200 (based on the inlet height and inlet velocity). The flow structure and heat transfer behavior is analyzed in detail for certain cases and the staggered and the inline tube arrangements are compared. Finally, for each of these arrangements the optimal sets of angles of attack for different Reynolds numbers are presented. Y1 - 2010 U6 - https://doi.org/10.1016/j.ijheatmasstransfer.2010.07.017 SN - 0017-9310 VL - 53 IS - 23/24 SP - 5386 EP - 5399 PB - Elsevier BV ER - TY - CHAP A1 - Raufeisen, A. A1 - Breuer, Michael A1 - Botsch, T. A1 - Delgado, A. T1 - Time-Dependent Three-Dimensional Simulation of the Turbulent Flow and Heat Transfer in Czochralski Crystal Growth Including the Three-Phase Boundary Movement T2 - High Performance Computing in Science and Engineering '10 N2 - In the literature, numerical computations of the Czochralski process for crystal growth are conducted using a quasi-steady state assumption for the crystallization neglecting time-dependent effects. In the present work, an algorithm is developed, which allows to calculate the transient behavior of the crystallization interface including the movement of the three-phase boundary and the free surface of the melt. Thus, in conjunction with the computation of the turbulent melt flow and heat transfer, more realistic predictions of the crystal growth can be achieved. Test cases show that with the algorithm, realistic phenomena like crystal diameter increase and decrease during the growth process could be reproduced. Y1 - 2011 SN - 9783642157479 U6 - https://doi.org/10.1007/978-3-642-15748-6_27 SP - 353 EP - 367 PB - Springer CY - Berlin, Heidelberg ER - TY - CHAP A1 - Lemouedda, A. A1 - Breuer, Michael A1 - Franz, E. T1 - Pareto optimization of heat transfer enhancement of finned-tube heat exchangers with delta-winglet vor-tex generators T2 - Turbulence, heat and mass transfer 6 : proceedings of the Sixth International Symposium on Turbulence, Heat and Mass Transfer Rome, Italy, 14 - 18 September, 2009 N2 - For circular finned tubes often used in heat exchangers, the wake regions behind the tubes are regions with low heat transfer coefficient. Delta-winglet vortex generators on the fin surfaces reduce the width of the wake regions and improve the overall heat transfer rate. The present work studies numerically the effect of enhancing the performance of the finned-tubes using delta-winglets. Simulations were carried out on a model of three circular tube rows with circular fins for Reynolds numbers of 500, 700, and 900 (based on the inlet velocity and the hydraulic diameter of unit cell). Eighteen basic configurations with different number and positions of delta-winglets were investigated. The flow and heat transfer behaviors are analyzed for certain configurations. Finally, the optimal configurations are presented based on the Pareto optimality strategy. Y1 - 2009 SN - 978–1–56700–262–1 U6 - https://doi.org/10.1615/ICHMT.2009.TurbulHeatMassTransf.1860 SN - 2377-2816 SP - 1015 EP - 1018 ER - TY - GEN A1 - Türk, Ben T1 - Planning of a test facility to investigate NOx reduction using the SNCR process for decentralized biomass boilers N2 - Poster Y1 - 2025 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:92-opus4-38028 ER - TY - JOUR A1 - Raufeisen, A. A1 - Breuer, Michael A1 - Botsch, T. A1 - Delgado, A. T1 - DNS of rotating buoyancy– and surface tension–driven flow JF - International Journal of Heat and Mass Transfer Y1 - 2008 U6 - https://doi.org/10.1016/j.ijheatmasstransfer.2008.01.041 SN - 0017-9310 VL - 51 IS - 25/26 SP - 6219 EP - 6234 PB - Elsevier BV ER - TY - CHAP A1 - Raufeisen, A. A1 - Breuer, Michael A1 - Botsch, T. A1 - Delgado, A. T1 - Analysis of Turbulent Structures in a Czochralski System Using DNS and LES Predictions T2 - High Performance Computing in Science and Engineering `07 N2 - A DNS of the turbulent flow and heat transfer in an idealized Czochralski configuration was conducted using a very fine grid. The results show the irregular forming of buoyant thermal plumes as well as the occurrence of a large, stable vortical structure in the bulk of the melt. In the averaged flow field a B´enard-cell-like pattern can be recognized. The DNS data served also as a reference for the validation of the LES method. The LES computations were conducted using different grid sizes, SGS models, and discretization methods. For relatively fine grids and central differences, the results agree very well with the DNS. Using an upwind discretization introduces numerical errors. In combination with coarser grids, this leads to large deviations and even qualitative differences. However, overall the computational effort could be reduced significantly by LES. Thus a compromise between accuracy achieved and effort required has to be found. Y1 - 2007 SN - 9783540747383 U6 - https://doi.org/10.1007/978-3-540-74739-0_25 SP - 371 EP - 386 PB - Springer CY - Berlin, Heidelberg ER - TY - JOUR A1 - Raufeisen, A. A1 - Breuer, Michael A1 - Botsch, T. A1 - Delgado, A. T1 - Transient 3D simulation of Czochralski crystal growth considering diameter variations JF - Journal of Crystal Growth N2 - For numerical simulations of the Czochralski crystal growth process, in the literature the quasi-steady state approach is used, i.e. the diameter of the crystal is kept constant. However, this leads to errors in the computation of the phase interface. In the present work, for the first time in 3D, the three-phase junction between melt, crystal and atmo-sphere is allowed to move in horizontal direction. Thus, diameter changes during the crystal growth process could be simulated accordingly. In the future, the vertical movement will be allowed as well, considering the free surface stresses. This will enable realistic predictions of the transient behavior of the crystallization front. Y1 - 2009 U6 - https://doi.org/10.1016/j.jcrysgro.2008.09.073 SN - 0022-0248 VL - 311 IS - 3 SP - 695 EP - 697 PB - Elsevier BV ER - TY - JOUR A1 - Raufeisen, A. A1 - Jana, S. A1 - Breuer, Michael A1 - Botsch, T. A1 - Durst, F. T1 - 3D computation of oxygen transport in Czochralski crystal growth of silicon considering evaporation JF - Journal of Crystal Growth N2 - For Czochralski (Cz) growth of silicon single crystals, 3D unsteady simulations of the oxygen transport in the turbulent melt flow were conducted using a new formulation for the evaporation at the free surface found by Sakai et al. [Electrochem. Solid-State Lett. 5 (8) (2002) G72]. Compared with 2D results from literature, the computed oxygen concentration now fits the experimental data better, showing lower values in the critical region beneath the crystal than in previous simulations, which mostly arises from the more accurate prediction of the flow field. Further computations of Cz configurations show how the oxygen distribution can be influenced by rotation of the crucible and crystal. Y1 - 2007 U6 - https://doi.org/10.1016/j.jcrysgro.2006.11.349 SN - 0022-0248 VL - 303 IS - 1 SP - 146 EP - 149 PB - Elsevier BV ER - TY - JOUR A1 - Raufeisen, Alexander A1 - Breuer, Michael A1 - Botsch, T. A1 - Delgado, A. T1 - LES validation of turbulent rotating buoyancy- and surface tension-driven flow against DNS JF - Computers & Fluids Y1 - 2009 U6 - https://doi.org/10.1016/j.compfluid.2009.01.002 SN - 0045-7930 VL - 38 IS - 8 SP - 1549 EP - 1565 PB - Elsevier BV ER - TY - JOUR A1 - Altun, Okay A1 - Prziwara, Paul A1 - Breitung-Faes, Sandra A1 - Kwade, Arno T1 - Impacts of process and design conditions of dry stirred milling on the shape of product size distribution JF - Minerals Engineering N2 - A grinding technology should consider the physical properties of the material, i.e., size, shape, which have effects on the product specifications, i.e., quality, strength or overall process efficiency. In this respect, this study aimed at evaluating the variations in the shape of product size distribution of a stirred media mill as the attention on this technology has been growing in the recent years. Within the scope of the research, series of grinding tests were performed at different operating conditions, i.e. bead size, bead type, tip speed, feed rate and mill design, with a laboratory scale continuously operated horizontal stirred media mill. The investigations proved that the use of coarser and denser beads as well as adjusting higher tip speeds resulted in obtaining narrower product size distribution for the same mean size. For a better understanding of the process, the stress energy and mean residence time evaluations were also undertaken. It was found that the stress energy and its normalization with the mean residence time are directly proportional to the slope of the distributions. As a conclusion, the dry stirred media mill is able to adjust the shape of the distribution, which may be beneficial regarding to the mechanical properties of the end products (cement manufacturing) or efficiency of the mineral beneficiation processes. KW - Grinding media KW - Dry stirred media milling KW - Process optimization KW - Product size distribution Y1 - 2021 U6 - https://doi.org/10.1016/j.mineng.2021.106806 SN - 0892-6875 VL - 163 PB - Elsevier BV ER - TY - JOUR A1 - Prziwara, Paul A1 - Thake, Simon A1 - Breitung-Faes, Sandra A1 - Kwade, Arno T1 - Comparison of open and closed circuit mode using a dry horizontal stirred media mill with special regard to the powder flowability and residence time distribution JF - Minerals Engineering N2 - A dry operated, horizontal stirred media mill was used for the fine grinding of limestone and compared in open and closed circuit modes. It was found that the choice of grinding aids as well as the stirrer tip speed are crucial for the mill operation, especially in terms of the grinding efficiency and the transport behavior through the mill. Independent of the process mode, both a too low and an excessive additive-induced flow behavior led to unfavorable stress conditions inside the mill, and thus, inefficient grinding. In the open circuit, especially high flowabilities turned out to be crucial, as thereby the stress conditions are negatively affected as a consequence of the material transport in combination with the overlapping impact of a mill- internal deflector wheel. Different important aspects were seen for the closed circuit grinding; especially when aiming for high finenesses or using high tip speeds, it is essential to ensure both a minimum flowability and a sufficient particle stabilization to ensure a fast removal of fine particles from the mill. High flowabilities in turn are not as critical during closed circuit grinding, but are accompanied by high material recirculations. KW - Dry continuous fine grinding KW - Open and closed circuit KW - Dry KW - Operated stirred media mill KW - Grinding aids KW - Powder behavior Y1 - 2021 U6 - https://doi.org/10.1016/j.mineng.2021.106781 SN - 0892-6875 VL - 163 PB - Elsevier BV ER - TY - CHAP A1 - Dibrova, Sofiia A1 - Appoldt, Leon A1 - Breitung-Faes, Sandra T1 - Influence of additives on classification and transportation efficiency in fine powder handling T2 - BOOK OF ABSTRACTS N2 - In this study, the effect of additives on very fine limestone powder was investigated for a fine limestone powder with regard to construction and pharmaceutical applications. Three different additives were considered in an attempt to reduce the tendency towards agglomeration and caking, which are occuring effect, reducing process efficiency and stability. The selection of these additives was based on their performance in previous studies on the limestone and lactose material systems during dry grinding [1] – [3]. Instead of grinding especially separation and transport processes were taken into account. To test the efficiency of the additives used, the sieving capacity of the powders, the separation behavior in a zig-zag air classifier as well as the flow behavior in a vibratory feeder were tested. Here, only the results of the sieve analysis for the additive heptanoic acid are described since heptanoic acid showed the most significant effect compared to the other additives. Additionally, the results of the dynamic image analysis, laser diffraction spectroscopy and the flowability measurements are provided and will be discussed. [1] P. Prziwara, S. Breitung-Faes, und A. Kwade, „Impact of grinding aids on dry grinding performance, bulk properties and surface energy“, Advanced Powder Technology, Bd. 29, Nr. 2, S. 416–425, Feb. 2018, doi: 10.1016/j.apt.2017.11.029. [2] L. Miethke, P. Prziwara, J. H. Finke, und S. Breitung-Faes, „Opposing Effects of Additives in Dry Milling and Tableting of Organic Particles“, Pharmaceutics, Bd. 13, Nr. 9, S. 1434, Sep. 2021, doi: 10.3390/pharmaceutics13091434. [3] P. Prziwara, L. D. Hamilton, S. Breitung-Faes, und A. Kwade, „Evaluation of the capturing of dry fine particles between grinding media by drop-weight tests“, Powder Technology, Bd. 363, S. 326–336, März 2020, doi: 10.1016/j.powtec.2020.01.012. Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:92-opus4-42745 SN - 978-3-18-990139-9 SN - 0083-5560 PB - VDI Verlag GmbH CY - Düsseldorf ER - TY - CHAP A1 - Dibrova, Sofiia A1 - Breitung-Faes, Sandra T1 - Modification of Powder Properties by Liquid Additives T2 - BOOK OF ABSTRACTS N2 - Additives are applied to dry, fine powders to achieve a wide range of objectives, including the reduction of energy consumption, refinement of particle size distributions, enhancement of product throughput or dosing behavior. These modifications often result in improvements in flowability, a reduction in agglomeration tendency, decreased frictional resistance, and the development of anti-stick properties. While numerous individual studies have investigated various additives across diverse processes, many results remain fragmented, and a comprehensive understanding of the mechanisms underlying the actions of different additives is still lacking. Consequently, the selection of suitable additives continues to rely predominantly on empirical knowledge. In this work, the addition of liquid additives from various substance classes to powders was investigated in greater detail. In particular, the effects of additive incorporation on the behavior of powders during interactions with other materials were examined—whether during the admixing of additives in different mixing systems or upon contact with various surfaces in the fluidized state, using a specially developed experimental setup. While simple geometries and varying process parameters can be tested in the experimental rig, practical testing of the additive products was also conducted in more complex systems. Simultaneously, other properties—e.g., changes in surface energy, dusting propensity, or agglomerate strength—were also studied. The results obtained aim to broaden the understanding of the effects of specific additive classes on products from different perspectives, thereby increasing the transparency and soundness of the additive selection process for diverse future applications. Y1 - 2025 SN - 978-3-18-990143-6 SN - 0083-5560 PB - VDI Verlag GmbH CY - Düsseldorf ER - TY - JOUR A1 - Mohan, Abhinav A1 - Ulmer, Ulrich A1 - Hurtado, Lourdes A1 - Loh, Joel A1 - Li, Young Feng A1 - Tountas, Athanasios A. A1 - Krevert, Carola A1 - Chan, Chakyu A1 - Liang, Yilei A1 - Brodersen, Peter A1 - Sain, Mohini M. A1 - Ozin, Geoffrey A. T1 - Hybrid Photo- and Thermal Catalyst System for Continuous CO2 Reduction JF - ACS Applied Materials & Interfaces N2 - Heterogeneous thermal catalytic processes are vital for industrial production of fuels, fertilizers, and other chemicals necessary for sustaining human life. However, these processes are highly energy-intensive, requiring a vast consumption of fossil fuels. An emerging class of heterogeneous catalysts that are thermally driven but also exhibit a photochemically enhanced rate can potentially reduce process energy intensity by partially substituting conventional heat (where fossil fuels are needed) with solar energy. Such catalyst systems have yet to be practically utilized. Here, we demonstrate a compact electrically heated photo- and thermal annular reactor module to reduce CO2 to CO, via the reverse water gas shift reaction. A first-principles-based design approach was taken in developing a SiO2 on an Al photo- and thermal catalyst system for the model photo- and thermal indium oxide hydroxide (In2O3–x(OH)y) catalysts. A 5-fold light enhancement in the CO production rate and over 70 h of stable CO production were achieved. This represents the highest light enhancement effect reported for this model photocatalyst to date. The reactor presented herein allows continuous operation and a significant reduction of 31% in heater power consumption when provided with an additional 2 suns of irradiation, demonstrating the strong photo- and thermal-harvesting performances of the catalyst system developed in this work. Y1 - 2020 U6 - https://doi.org/10.1021/acsami.0c06232 SN - 1944-8244 VL - 12 IS - 30 SP - 33613 EP - 33620 PB - American Chemical Society (ACS) ER - TY - JOUR A1 - Gerhard, Daniel A1 - Kramarska, Katarzyna A1 - Ulmer, Ulrich T1 - Exploring Hydrogen Technology Adoption in the German Energy Sector — A Dynamic Capabilities Perspective JF - Sustainability N2 - The transition to hydrogen is an important element of the sustainable transition of Germany’s industry. Regional German municipal utilities play a key role in this transition, as they are at the core position between local demand and regional supply. They play an important role when it comes to planned infrastructure development on the regional level. As energy infrastructure development is a long-term project, they need to deal with the hydrogen transition at a very early stage, including pilot projects, organizational changes, and business model adaptations. Yet, not much is known about how these entities organize the transition to hydrogen. Using a qualitative research approach, this study takes a dynamic-capability perspective to shed light on the hydrogen transition activities of German municipal utilities. Industry and other energy sector participants can learn from these insights on how to organize the transition path towards hydrogen. Findings indicate that strong partnerships play a key role in identifying new opportunities and that balancing risk and benefit is a key challenge when it comes to realizing new technological hydrogen projects. KW - hydrogen adoption; dynamic capabilities; technology adoption Y1 - 2025 U6 - https://doi.org/10.3390/su172310545 VL - 17 ER - TY - JOUR A1 - Dong, Yuchan A1 - Duchesne, Paul A1 - Mohan, Abhinav A1 - Ghuman, Kulbir Kaur A1 - Kant, Paul A1 - Hurtado, Lourdes A1 - Ulmer, Ulrich A1 - Loh, Joel Y. Y. A1 - Tountas, Athanasios A. A1 - Wang, Lu A1 - Ali, Feysal M. A1 - Xia, Meikun A1 - Dittmeyer, Roland A1 - Ozin, Geoffrey A. T1 - Shining light on CO2: from materials discovery to photocatalyst, photoreactor and process engineering JF - Chemical Society Reviews N2 - Heterogeneous catalysis, a process in which the reaction of gaseous or liquid chemical reagents is facilitated at the surface of a solid material, is responsible for the majority of industrial-scale chemical and fuel production reactions. The energy required to drive these reactions has historically been derived from the combustion of non-renewable fossil fuels and carries an unavoidably large carbon footprint. More recently, the development of environmentally responsible and sustainable chemical industries is increasingly motivated by greenhouse gas-induced climate change, thus creating demand for eco-friendly heterogeneous catalytic processes. This includes innovative approaches enabled by renewable forms of energy, such as the electrification of chemical and petrochemical processes, utilization of CO2 as a feedstock and the incorporation of light into catalytic reactions. Herein we review the conversion of solar energy to chemical energy using CO2, and describe how the photophysical and photochemical properties of nanostructured metal oxide photocatalysts have been engineered to efficiently incorporate light into heterogeneous gas–solid CO2 hydrogenation reactions. Realizing high photonic and energy efficiencies in these systems has demanded innovation in not only photocatalyst engineering, but also photoreactor and process engineering. Rather than exclusively providing an in-depth discussion of the chemistry and science within each individual study, this Tutorial Review highlights the multidisciplinary character of photocatalysis studies by covering the four essential components of a typical research work in this field (materials engineering, theoretical modelling, reactor engineering and process development) via case studies of the archetypal indium oxide catalyst materials. Through advances in these four components, progress has been made towards the ultimate goal of industrializing the production of CO2-derived chemicals and fuels. Y1 - 2020 U6 - https://doi.org/10.1039/D0CS00597E SN - 0306-0012 VL - 49 IS - 16 SP - 5648 EP - 5663 PB - Royal Society of Chemistry (RSC) ER - TY - JOUR A1 - Guo, Jiuli A1 - Duchesne, Paul N. A1 - Wang, Lu A1 - Song, Rui A1 - Xia, Meikun A1 - Ulmer, Ulrich A1 - Sun, Wei A1 - Dong, Yuchan A1 - Loh, Joel Y. Y. A1 - Kherani, Nazir P. A1 - Du, Jimin A1 - Zhu, Baolin A1 - Huang, Weiping A1 - Zhang, Shoumin A1 - Ozin, Geoffrey A. T1 - High-Performance, Scalable, and Low-Cost Copper Hydroxyapatite for Photothermal CO2 Reduction JF - ACS Catalysis Y1 - 2020 U6 - https://doi.org/10.1021/acscatal.0c03806 SN - 2155-5435 VL - 10 IS - 22 SP - 13668 EP - 13681 PB - American Chemical Society (ACS) ER - TY - JOUR A1 - Neberich, Marcel A1 - Opferkuch, Frank T1 - Standardizing Melanopic Effects of Ocular Light for Ecological Lighting Design of Nonresidential Buildings—An Overview of Current Legislation and Accompanying Scientific Studies JF - Sustainability N2 - DIN SPEC 5031-100 and CIE S 026:2018 are regulatory frameworks that are intended to establish health-preserving indoor lighting in Europe. Therefore, they are crucial for the visual environment and its sustainability. The standards are largely congruent. Inconsistencies should now be harmonized with the newly published draft standard DIN/TS 5031-100, for which the objection period ended on 3 June 2020; thus, it can be expected that the standard will soon be put into operation. This publication provides the reader with a detailed technical as well as medical overview of the scope and background information on how the standard came about. Applicable laws, ordinances and standards were compiled across countries, and related studies were reviewed. It is demonstrated that the focus of this new standard, as with previous versions, is on the melanopic sensitivity of ganglion cells. The authors base this on a literature search for projects about ecological lighting design over the past 20 years. However, in practice, the publication of the standard does not yet completely counteract the health effects of inappropriate indoor lighting. KW - human centric lighting KW - standardization KW - DIN/TS 5031-100 KW - melanopic effect Y1 - 2021 U6 - https://doi.org/10.3390/su13095131 SN - 2071-1050 VL - 13 IS - 9 PB - MDPI AG ER - TY - JOUR A1 - Xia, Meikun A1 - Mao, Chengliang A1 - Gu, Alan A1 - Tountas, Athanasios A. A1 - Qiu, Chenyue A1 - Wood, Thomas E. A1 - Li, Young Feng A1 - Ulmer, Ulrich A1 - Xu, Yangfan A1 - Viasus, Camilo J. A1 - Ye, Jessica A1 - Qian, Chenxi A1 - Ozin, Geoffrey T1 - Solar Urea: Towards a Sustainable Fertilizer Industry JF - Angewandte Chemie N2 - Urea, an agricultural fertilizer, nourishes humanity. The century‐old Bosch–Meiser process provides the world's urea. It is multi‐step, consumes enormous amounts of non‐renewable energy, and has a large CO2 footprint. Thus, developing an eco‐friendly synthesis for urea is a priority. Herein we report a single‐step Pd/LTA‐3A catalyzed synthesis of urea from CO2 and NH3 under ambient conditions powered solely by solar energy. Pd nanoparticles serve the dual function of catalyzing the dissociation of NH3 and providing the photothermal driving force for urea formation, while the absorption capacity of LTA‐3A removes by‐product H2O to shift the equilibrium towards urea production. The solar urea conversion rate from NH3 and CO2 is 87 μmol g−1 h−1. This advance represents a first step towards the use of solar energy in urea production. It provides insights into green fertilizer production, and inspires the vision of sustainable, modular plants for distributed production of urea on farms. Y1 - 2021 U6 - https://doi.org/10.1002/ange.202110158 SN - 0044-8249 VL - 134 IS - 1 PB - Wiley ER - TY - JOUR A1 - Hurtado, Lourdes A1 - Mohan, Abhinav A1 - Ulmer, Ulrich A1 - Natividad, Reyna A1 - Tountas, Athanasios A. A1 - Sun, Wei A1 - Wang, Lu A1 - Kim, Boeun A1 - Sain, Mohini M. A1 - Ozin, Geoffrey A. T1 - Solar CO2hydrogenation by photocatalytic foams JF - Chemical Engineering Journal N2 - Here we report the enhanced light penetration and mass transfer efficiency of photocatalytic foams to convert CO2 to CO. The viability of utilizing a metallic foam as a model photocatalyst support is used to evaluate the photochemical and thermochemical reverse water gas shift reaction catalyzed by photoactive indium oxide hydroxide nanorods uniformly coated on nickel foams. A light-enhanced CO production rate up to 130% higher than the dark CO production was achieved through enhanced light penetration. A remarkably high thermo- chemical CO production rate of 0.75 mmol gcat 1 h 1 was achieved at 295 ◦C. Whilst several approaches to optimization of photocatalyst morphology at the nanoscale have been successful in extending electron hole-pair lifetime and modifying the site of reactions, these advantages cannot be significantly realized unless microscale to macroscale structuring efforts, that shorten the path length for diffusion of the reactant gas molecule and lengthen photon penetration to these catalytic sites are integrated. The superior catalytic performance of the indium oxide hydroxide nanorods on an optimized coated foam configuration compared to the performance of packed bed and thin film configurations demonstrates the critical importance of using structured supports in scale up of future photocatalytic processes. Y1 - 2022 U6 - https://doi.org/10.1016/j.cej.2022.134864 SN - 1385-8947 VL - 435 PB - Elsevier BV ER -