@article{ChairopoulouGarciaTrinanesTeipel2022, author = {Chairopoulou, Makrina A. and Garcia-Tri{\~n}anes, Pablo and Teipel, Ulrich}, title = {Oyster shell reuse: A particle engineering perspective for the use as emulsion stabilizers}, series = {Powder Technology}, volume = {408}, journal = {Powder Technology}, publisher = {Elsevier BV}, issn = {0032-5910}, doi = {10.1016/j.powtec.2022.117721}, pages = {13}, year = {2022}, abstract = {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.}, language = {en} } @article{KuglerAumuellerKrcmaretal.2022, author = {Kugler, Felix and Aum{\"u}ller, Jessica and Krcmar, Wolfgang and Teipel, Ulrich}, title = {Construction and Demolition Residuals as Raw Materials for the Production of Novel Geopolymer Building Materials}, series = {Crystals}, volume = {12}, journal = {Crystals}, number = {5}, publisher = {MDPI AG}, issn = {2073-4352}, doi = {10.3390/cryst12050678}, year = {2022}, abstract = {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.}, language = {en} } @article{KuglerFehnSandneretal.2022, author = {Kugler, Felix and Fehn, Thomas and Sandner, Maximilian and Krcmar, Wolfgang and Teipel, Ulrich}, title = {Microstructural and mechanical properties of geopolymers based on brick scrap and fly ash}, series = {International Journal of Ceramic Engineering \& Science}, volume = {4}, journal = {International Journal of Ceramic Engineering \& Science}, number = {2}, publisher = {Wiley}, issn = {2578-3270}, doi = {10.1002/ces2.10120}, pages = {92 -- 101}, year = {2022}, abstract = {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.}, language = {en} } @article{KuglerKarrerKrcmaretal.2022, author = {Kugler, Felix and Karrer, J{\"o}rg and Krcmar, Wolfgang and Teipel, Ulrich}, title = {Setting behavior and mechanical properties of concrete rubble fly ash geopolymers}, series = {Open Ceramics}, volume = {11}, journal = {Open Ceramics}, publisher = {Elsevier BV}, issn = {2666-5395}, doi = {10.1016/j.oceram.2022.100286}, pages = {11}, year = {2022}, abstract = {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.}, language = {en} } @article{Teipel2022, author = {Teipel, Ulrich}, title = {New separation function for the stationary screening process}, series = {The Canadian Journal of Chemical Engineering}, volume = {100}, journal = {The Canadian Journal of Chemical Engineering}, number = {9}, publisher = {Wiley}, issn = {0008-4034}, doi = {10.1002/cjce.24416}, pages = {2347 -- 2354}, year = {2022}, abstract = {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.}, language = {en} } @article{ChairopoulouKokkinosGarciaTrinanesetal.2021, author = {Chairopoulou, Makrina A. and Kokkinos, Nikolaos and Garcia-Tri{\~n}anes, Pablo and Mitropoulos, Athanassios C. and Teipel, Ulrich}, title = {Evaluation of particle recovery from microalgae}, series = {Advanced Powder Technology}, volume = {32}, journal = {Advanced Powder Technology}, number = {8}, publisher = {Elsevier BV}, issn = {0921-8831}, doi = {10.1016/j.apt.2021.06.013}, pages = {3023 -- 3033}, year = {2021}, abstract = {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.}, language = {en} } @article{EisenlauerTeipel2021, author = {Eisenlauer, Moritz and Teipel, Ulrich}, title = {Comminution energy and particulate properties of cutting and hammer-milled beech, oak, and spruce wood}, series = {Powder Technology}, volume = {394}, journal = {Powder Technology}, publisher = {Elsevier BV}, issn = {0032-5910}, doi = {10.1016/j.powtec.2021.03.072}, pages = {685 -- 704}, year = {2021}, abstract = {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.}, language = {en} } @article{ChairopoulouKratzerGrossetal.2020, author = {Chairopoulou, Makrina A. and Kratzer, Fabian and Groß, Roland and Herrmann, Michael and Teipel, Ulrich}, title = {Influence of the Temperature on Coccolith-Containing Systems from Emiliania huxleyi Cultivations}, series = {Chemical Engineering \& Technology}, volume = {43}, journal = {Chemical Engineering \& Technology}, number = {5}, publisher = {Wiley}, issn = {0930-7516}, doi = {10.1002/ceat.201900507}, pages = {904 -- 912}, year = {2020}, abstract = {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.}, language = {en} } @article{DreselTeipel2020, author = {Dresel, Alexander and Teipel, Ulrich}, title = {Jet Dispersion of Multiwall Carbon Nanotubes and Correlation with Suspension Rheology}, series = {Chemical Engineering \& Technology}, volume = {43}, journal = {Chemical Engineering \& Technology}, number = {5}, publisher = {Wiley}, issn = {0930-7516}, doi = {10.1002/ceat.201900534}, pages = {869 -- 878}, year = {2020}, abstract = {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.}, language = {en} } @article{EisenlauerTeipel2020, author = {Eisenlauer, Moritz and Teipel, Ulrich}, title = {Comminution of Wood - Influence of Process Parameters}, series = {Chemical Engineering \& Technology}, volume = {43}, journal = {Chemical Engineering \& Technology}, number = {5}, publisher = {Wiley}, issn = {0930-7516}, doi = {10.1002/ceat.201900488}, pages = {838 -- 847}, year = {2020}, abstract = {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.}, language = {en} } @article{TeipelWolfSchreiber2020, author = {Teipel, Ulrich and Wolf, Sebastian and Schreiber, Alex}, title = {Durchgangswiderstand von partikul{\"a}ren Systemen}, series = {Chemie Ingenieur Technik}, volume = {92}, journal = {Chemie Ingenieur Technik}, number = {3}, publisher = {Wiley}, issn = {0009-286X}, doi = {10.1002/cite.201800141}, pages = {229 -- 237}, year = {2020}, abstract = {Die elektrischen Eigenschaften von Partikeln insbesondere der Durchgangswiderstand von Partikelsch{\"u}ttungen 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 Festk{\"o}rper unterscheidet, ist der Durchgangswiderstand entscheidend von den Produkteigenschaften der Partikel und des Fluids abh{\"a}ngig. Im Rahmen dieser Arbeit wurde die Abh{\"a}ngigkeit des Durchgangswiderstandes von der inneren Struktur der Sch{\"u}ttung, der relativen Feuchtigkeit, der Konditionierungszeit bei unterschiedlichem Klima und der mittleren Partikelgr{\"o}ße in einer konzentrischen Messzelle untersucht.}, language = {en} } @article{GundermannRaabRaabetal.2021, author = {Gundermann, Michael and Raab, Florian and Raab, Daniel and Botsch, Tilman}, title = {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}, series = {International Journal of Heat and Mass Transfer}, volume = {170}, journal = {International Journal of Heat and Mass Transfer}, publisher = {Elsevier BV}, issn = {0017-9310}, doi = {10.1016/j.ijheatmasstransfer.2021.121016}, pages = {15}, year = {2021}, abstract = {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.}, language = {en} } @incollection{WeersWollmannTeipeletal.2020, author = {Weers, Martin and Wollmann, Annett and Teipel, Ulrich and Weber, Alfred P.}, title = {Dynamics of Separation Characteristics of Sieving and Flow Classification Processes}, series = {Dynamic Flowsheet Simulation of Solids Processes}, booktitle = {Dynamic Flowsheet Simulation of Solids Processes}, publisher = {Springer International Publishing}, address = {Cham}, isbn = {9783030451677}, doi = {10.1007/978-3-030-45168-4_10}, pages = {349 -- 390}, year = {2020}, language = {en} } @incollection{RaufeisenBreuerKumaretal.2007, author = {Raufeisen, A. and Breuer, M. and Kumar, V. and Botsch, Tilman and Durst, F.}, title = {LES and DNS of Melt Flow and Heat Transfer in Czochralski Crystal Growth}, series = {High Performance Computing in Science and Engineering '06}, booktitle = {High Performance Computing in Science and Engineering '06}, publisher = {Springer}, address = {Berlin, Heidelberg}, isbn = {9783540361657}, doi = {10.1007/978-3-540-36183-1_20}, pages = {279 -- 291}, year = {2007}, abstract = {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.}, language = {en} } @incollection{RaufeisenBotschKumaretal.2007, author = {Raufeisen, A. and Botsch, Tilman and Kumar, V. and Breuer, M. and Durst, F.}, title = {Prediction of Flow and Heat Transfer in a Czochralski Crucible using LES with Interface Tracking}, series = {Springer Proceedings in Physics}, booktitle = {Springer Proceedings in Physics}, publisher = {Springer}, address = {Berlin, Heidelberg}, isbn = {9783540326021}, doi = {10.1007/978-3-540-32603-8_59}, pages = {289 -- 292}, year = {2007}, language = {en} } @misc{NeumeisterReichelPriscoPetryetal.2024, author = {Neumeister, Roberta Fatima and Reichel, Christoph and Prisco Petry, Adriane and Vi{\c{c}}osa M{\"o}ller, Sergio}, title = {NUMERICAL ANALYSIS OF FLOW INTERACTIONS WITHIN A BANK OF TUBES WITH CLOSE SPACE RATIO}, series = {FIV-2024-0052, FIV2024; FSI \& FIV + N 10th Symposium on Fluid-Structure Interactions, Flow-sound Interactions, Flow-Induced Vibration \& Noise}, journal = {FIV-2024-0052, FIV2024; FSI \& FIV + N 10th Symposium on Fluid-Structure Interactions, Flow-sound Interactions, Flow-Induced Vibration \& Noise}, pages = {8}, year = {2024}, abstract = {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.}, language = {en} } @techreport{ReichelReichel2024, author = {Reichel, Christoph and Reichel, Philip}, title = {Simulation of Tube Bundle Vibrations with CFX10}, publisher = {Mendeley Data}, year = {2024}, abstract = {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.}, language = {en} } @article{NoeskeMuellerNowaketal.2022, author = {N{\"o}ske, Markus and M{\"u}ller, Jannes and Nowak, Christine and Li, Kangqi and Xu, Xiaolu and Breitung-Faes, Sandra and Kwade, Arno}, title = {Multicomponent Comminution within a Stirred Media Mill and Its Application for Processing a Lithium-Ion Battery Slurry}, series = {Processes}, volume = {10}, journal = {Processes}, number = {11}, publisher = {MDPI AG}, issn = {2227-9717}, doi = {10.3390/pr10112309}, pages = {25}, year = {2022}, abstract = {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.}, language = {en} } @article{MiethkePrziwaraFinkeetal.2021, author = {Miethke, Lina and Prziwara, Paul and Finke, Jan Henrik and Breitung-Faes, Sandra}, title = {Opposing Effects of Additives in Dry Milling and Tableting of Organic Particles}, series = {Pharmaceutics}, volume = {13}, journal = {Pharmaceutics}, number = {9}, publisher = {MDPI AG}, issn = {1999-4923}, doi = {10.3390/pharmaceutics13091434}, pages = {26}, year = {2021}, abstract = {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.}, language = {en} } @article{BotschStumpmeierGanser2010, author = {Botsch, T. W. and Stumpmeier, S. and Ganser, J.}, title = {Simulation of the transient condensation process in steam pipes during start up of a steam power plant}, series = {Heat and Mass Transfer}, volume = {46}, journal = {Heat and Mass Transfer}, number = {10}, publisher = {Springer Science and Business Media LLC}, issn = {0947-7411}, doi = {10.1007/s00231-010-0714-3}, pages = {1187 -- 1197}, year = {2010}, abstract = {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.}, language = {en} } @inproceedings{NeumeisterReichelPriscoPetryetal.2023, author = {Neumeister, Roberta Fatima and Reichel, Christoph and Prisco Petry, Adriane and M{\"o}ller, Sergio Vi{\c{c}}osa}, title = {Numerical analysis of crossflow over one and two rows of cylinders}, series = {Proceedings of the 27th International Congress of Mechanical Engineering}, booktitle = {Proceedings of the 27th International Congress of Mechanical Engineering}, publisher = {ABCM}, doi = {10.26678/ABCM.COBEM2023.COB2023-0404}, year = {2023}, abstract = {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.}, language = {en} } @article{SterlingBreitungFaesKwade2024, author = {Sterling, David and Breitung-Faes, Sandra and Kwade, Arno}, title = {Improved energy transfer model for mechanistic scale-up of stirred media mills}, series = {Powder Technology}, volume = {444}, journal = {Powder Technology}, publisher = {Elsevier BV}, issn = {0032-5910}, doi = {10.1016/j.powtec.2024.119978}, pages = {14}, year = {2024}, abstract = {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.}, language = {en} } @article{PeppersackFlachPrziwaraetal.2023, author = {Peppersack, Christoph and Flach, Frederik and Prziwara, Paul and Damm, Cornelia and Breitung-Faes, Sandra and Peukert, Wolfgang and Kwade, Arno}, title = {Conceptual stabilizer selection for nanomilling based on dispersibility parameters}, series = {Advanced Powder Technology}, volume = {34}, journal = {Advanced Powder Technology}, number = {10}, publisher = {Elsevier BV}, issn = {0921-8831}, doi = {10.1016/j.apt.2023.104197}, pages = {12}, year = {2023}, abstract = {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.}, language = {en} } @article{PeppersackKwadeBreitungFaes2021, author = {Peppersack, Christoph and Kwade, Arno and Breitung-Faes, Sandra}, title = {Selective particle size analysis in binary submicron particle mixtures using density dependent differential sedimentation}, series = {Advanced Powder Technology}, volume = {32}, journal = {Advanced Powder Technology}, number = {11}, publisher = {Elsevier BV}, issn = {0921-8831}, doi = {10.1016/j.apt.2021.09.010}, pages = {4049 -- 4057}, year = {2021}, abstract = {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.}, language = {en} } @article{SterlingBreitungFaesKwade2023, author = {Sterling, David and Breitung-Faes, Sandra and Kwade, Arno}, title = {Experimental evaluation of the energy transfer within wet operated stirred media mills}, series = {Powder Technology}, volume = {425}, journal = {Powder Technology}, publisher = {Elsevier BV}, issn = {0032-5910}, doi = {10.1016/j.powtec.2023.118579}, pages = {17}, year = {2023}, abstract = {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.}, language = {en} } @article{PeppersackWermbterKwadeetal.2022, author = {Peppersack, Christoph and Wermbter, Karsten and Kwade, Arno and Garnweitner, Georg and Breitung-Faes, Sandra}, title = {Top-Down Formulation of Goethite Nanosuspensions for the Production of Transparent, Inorganic Glass Coatings}, series = {Coatings}, volume = {12}, journal = {Coatings}, number = {3}, publisher = {MDPI AG}, issn = {2079-6412}, doi = {10.3390/coatings12030330}, pages = {18}, year = {2022}, abstract = {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.}, language = {en} } @article{SterlingSchonsBreitungFaesetal.2022, author = {Sterling, David and Schons, Didier and Breitung-Faes, Sandra and Kwade, Arno}, title = {Effects of axial grinding media distribution on the disc wear behavior of a stirred media mill}, series = {Minerals Engineering}, volume = {185}, journal = {Minerals Engineering}, publisher = {Elsevier BV}, issn = {0892-6875}, doi = {10.1016/j.mineng.2022.107702}, pages = {11}, year = {2022}, abstract = {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.}, language = {en} } @article{CaiPengSongetal.2022, author = {Cai, Yingying and Peng, Wentao and Song, Qingyuan and Pluta, Denis and Peppersack, Christoph and Breitung-Faes, Sandra and Kwade, Arno and Bigall, Nadja C. and Vana, Philipp}, title = {Nanoengineering of Egyptian Blue Nanosheets: Advantages and Limitations for Near-Infrared Photoluminescence Applications}, series = {ACS Applied Optical Materials}, volume = {1}, journal = {ACS Applied Optical Materials}, number = {1}, publisher = {American Chemical Society (ACS)}, issn = {2771-9855}, doi = {10.1021/acsaom.2c00114}, pages = {465 -- 472}, year = {2022}, abstract = {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.}, language = {en} } @article{KwadeMoellerMuelleretal.2023, author = {Kwade, Arno and M{\"o}ller, Marcel and M{\"u}ller, Jannes and Hesselbach, Jutta and Zellmer, Sabrina and Doose, Stefan and Mayer, Julian and Michalowski, Peter and Powell, Malcolm and Breitung-Faes, Sandra}, title = {Comminution and Classification as Important Process Steps for the Circular Production of Lithium Batteries}, series = {KONA Powder and Particle Journal}, volume = {40}, journal = {KONA Powder and Particle Journal}, number = {0}, publisher = {Hosokawa Powder Technology Foundation}, issn = {0288-4534}, doi = {10.14356/kona.2023006}, pages = {50 -- 73}, year = {2023}, abstract = {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.}, language = {en} } @article{RaufeisenBreuerBotschetal.2010, author = {Raufeisen, A. and Breuer, Michael and Botsch, T. and Delgado, A.}, title = {Prediction of the three-phase boundary movement in Czochralski crystal growth}, series = {Journal of Crystal Growth}, volume = {312}, journal = {Journal of Crystal Growth}, number = {16/17}, publisher = {Elsevier BV}, issn = {0022-0248}, doi = {10.1016/j.jcrysgro.2010.05.009}, pages = {2297 -- 2299}, year = {2010}, abstract = {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.}, language = {en} } @article{LemoueddaBreuerFranzetal.2010, author = {Lemouedda, A. and Breuer, Michael and Franz, E. and Botsch, T. and Delgado, A.}, title = {Optimization of the angle of attack of delta-winglet vortex generators in a plate-fin-and-tube heat exchanger}, series = {International Journal of Heat and Mass Transfer}, volume = {53}, journal = {International Journal of Heat and Mass Transfer}, number = {23/24}, publisher = {Elsevier BV}, issn = {0017-9310}, doi = {10.1016/j.ijheatmasstransfer.2010.07.017}, pages = {5386 -- 5399}, year = {2010}, abstract = {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.}, language = {en} } @incollection{RaufeisenBreuerBotschetal.2011, author = {Raufeisen, A. and Breuer, Michael and Botsch, T. and Delgado, A.}, title = {Time-Dependent Three-Dimensional Simulation of the Turbulent Flow and Heat Transfer in Czochralski Crystal Growth Including the Three-Phase Boundary Movement}, series = {High Performance Computing in Science and Engineering '10}, booktitle = {High Performance Computing in Science and Engineering '10}, publisher = {Springer}, address = {Berlin, Heidelberg}, isbn = {9783642157479}, doi = {10.1007/978-3-642-15748-6_27}, pages = {353 -- 367}, year = {2011}, abstract = {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.}, language = {en} } @incollection{LemoueddaBreuerFranz2009, author = {Lemouedda, A. and Breuer, Michael and Franz, E.}, title = {Pareto optimization of heat transfer enhancement of finned-tube heat exchangers with delta-winglet vor-tex generators}, series = {Turbulence, heat and mass transfer 6 : proceedings of the Sixth International Symposium on Turbulence, Heat and Mass Transfer Rome, Italy, 14 - 18 September, 2009}, booktitle = {Turbulence, heat and mass transfer 6 : proceedings of the Sixth International Symposium on Turbulence, Heat and Mass Transfer Rome, Italy, 14 - 18 September, 2009}, isbn = {978-1-56700-262-1}, issn = {2377-2816}, doi = {10.1615/ICHMT.2009.TurbulHeatMassTransf.1860}, pages = {1015 -- 1018}, year = {2009}, abstract = {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.}, language = {en} } @misc{Tuerk2025, author = {T{\"u}rk, Ben}, title = {Planning of a test facility to investigate NOx reduction using the SNCR process for decentralized biomass boilers}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:92-opus4-38028}, year = {2025}, abstract = {Poster}, language = {en} } @article{RaufeisenBreuerBotschetal.2008, author = {Raufeisen, A. and Breuer, Michael and Botsch, T. and Delgado, A.}, title = {DNS of rotating buoyancy- and surface tension-driven flow}, series = {International Journal of Heat and Mass Transfer}, volume = {51}, journal = {International Journal of Heat and Mass Transfer}, number = {25/26}, publisher = {Elsevier BV}, issn = {0017-9310}, doi = {10.1016/j.ijheatmasstransfer.2008.01.041}, pages = {6219 -- 6234}, year = {2008}, language = {en} } @incollection{RaufeisenBreuerBotschetal.2007, author = {Raufeisen, A. and Breuer, Michael and Botsch, T. and Delgado, A.}, title = {Analysis of Turbulent Structures in a Czochralski System Using DNS and LES Predictions}, series = {High Performance Computing in Science and Engineering `07}, booktitle = {High Performance Computing in Science and Engineering `07}, publisher = {Springer}, address = {Berlin, Heidelberg}, isbn = {9783540747383}, doi = {10.1007/978-3-540-74739-0_25}, pages = {371 -- 386}, year = {2007}, abstract = {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.}, language = {en} } @article{RaufeisenBreuerBotschetal.2009, author = {Raufeisen, A. and Breuer, Michael and Botsch, T. and Delgado, A.}, title = {Transient 3D simulation of Czochralski crystal growth considering diameter variations}, series = {Journal of Crystal Growth}, volume = {311}, journal = {Journal of Crystal Growth}, number = {3}, publisher = {Elsevier BV}, issn = {0022-0248}, doi = {10.1016/j.jcrysgro.2008.09.073}, pages = {695 -- 697}, year = {2009}, abstract = {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.}, language = {en} } @article{RaufeisenJanaBreueretal.2007, author = {Raufeisen, A. and Jana, S. and Breuer, Michael and Botsch, T. and Durst, F.}, title = {3D computation of oxygen transport in Czochralski crystal growth of silicon considering evaporation}, series = {Journal of Crystal Growth}, volume = {303}, journal = {Journal of Crystal Growth}, number = {1}, publisher = {Elsevier BV}, issn = {0022-0248}, doi = {10.1016/j.jcrysgro.2006.11.349}, pages = {146 -- 149}, year = {2007}, abstract = {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.}, language = {en} } @article{RaufeisenBreuerBotschetal.2009, author = {Raufeisen, Alexander and Breuer, Michael and Botsch, T. and Delgado, A.}, title = {LES validation of turbulent rotating buoyancy- and surface tension-driven flow against DNS}, series = {Computers \& Fluids}, volume = {38}, journal = {Computers \& Fluids}, number = {8}, publisher = {Elsevier BV}, issn = {0045-7930}, doi = {10.1016/j.compfluid.2009.01.002}, pages = {1549 -- 1565}, year = {2009}, language = {en} } @article{AltunPrziwaraBreitungFaesetal.2021, author = {Altun, Okay and Prziwara, Paul and Breitung-Faes, Sandra and Kwade, Arno}, title = {Impacts of process and design conditions of dry stirred milling on the shape of product size distribution}, series = {Minerals Engineering}, volume = {163}, journal = {Minerals Engineering}, publisher = {Elsevier BV}, issn = {0892-6875}, doi = {10.1016/j.mineng.2021.106806}, pages = {12}, year = {2021}, abstract = {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.}, language = {en} } @article{PrziwaraThakeBreitungFaesetal.2021, author = {Prziwara, Paul and Thake, Simon and Breitung-Faes, Sandra and Kwade, Arno}, title = {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}, series = {Minerals Engineering}, volume = {163}, journal = {Minerals Engineering}, publisher = {Elsevier BV}, issn = {0892-6875}, doi = {10.1016/j.mineng.2021.106781}, pages = {12}, year = {2021}, abstract = {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.}, language = {en} } @inproceedings{DibrovaAppoldtBreitungFaes2023, author = {Dibrova, Sofiia and Appoldt, Leon and Breitung-Faes, Sandra}, title = {Influence of additives on classification and transportation efficiency in fine powder handling}, series = {BOOK OF ABSTRACTS}, booktitle = {BOOK OF ABSTRACTS}, publisher = {VDI Verlag GmbH}, address = {D{\"u}sseldorf}, isbn = {978-3-18-990139-9}, issn = {0083-5560}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:92-opus4-42745}, pages = {778 - 785}, year = {2023}, abstract = {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, M{\"a}rz 2020, doi: 10.1016/j.powtec.2020.01.012.}, language = {en} } @inproceedings{DibrovaBreitungFaes2025, author = {Dibrova, Sofiia and Breitung-Faes, Sandra}, title = {Modification of Powder Properties by Liquid Additives}, series = {BOOK OF ABSTRACTS}, booktitle = {BOOK OF ABSTRACTS}, publisher = {VDI Verlag GmbH}, address = {D{\"u}sseldorf}, isbn = {978-3-18-990143-6}, issn = {0083-5560}, pages = {179}, year = {2025}, abstract = {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.}, language = {en} } @article{MohanUlmerHurtadoetal.2020, author = {Mohan, Abhinav and Ulmer, Ulrich and Hurtado, Lourdes and Loh, Joel and Li, Young Feng and Tountas, Athanasios A. and Krevert, Carola and Chan, Chakyu and Liang, Yilei and Brodersen, Peter and Sain, Mohini M. and Ozin, Geoffrey A.}, title = {Hybrid Photo- and Thermal Catalyst System for Continuous CO2 Reduction}, series = {ACS Applied Materials \& Interfaces}, volume = {12}, journal = {ACS Applied Materials \& Interfaces}, number = {30}, publisher = {American Chemical Society (ACS)}, issn = {1944-8244}, doi = {10.1021/acsami.0c06232}, pages = {33613 -- 33620}, year = {2020}, abstract = {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.}, language = {en} } @article{GerhardKramarskaUlmer2025, author = {Gerhard, Daniel and Kramarska, Katarzyna and Ulmer, Ulrich}, title = {Exploring Hydrogen Technology Adoption in the German Energy Sector — A Dynamic Capabilities Perspective}, series = {Sustainability}, volume = {17}, journal = {Sustainability}, doi = {10.3390/su172310545}, pages = {16}, year = {2025}, abstract = {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.}, language = {en} } @article{DongDuchesneMohanetal.2020, author = {Dong, Yuchan and Duchesne, Paul and Mohan, Abhinav and Ghuman, Kulbir Kaur and Kant, Paul and Hurtado, Lourdes and Ulmer, Ulrich and Loh, Joel Y. Y. and Tountas, Athanasios A. and Wang, Lu and Ali, Feysal M. and Xia, Meikun and Dittmeyer, Roland and Ozin, Geoffrey A.}, title = {Shining light on CO2: from materials discovery to photocatalyst, photoreactor and process engineering}, series = {Chemical Society Reviews}, volume = {49}, journal = {Chemical Society Reviews}, number = {16}, publisher = {Royal Society of Chemistry (RSC)}, issn = {0306-0012}, doi = {10.1039/D0CS00597E}, pages = {5648 -- 5663}, year = {2020}, abstract = {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.}, language = {en} } @article{GuoDuchesneWangetal.2020, author = {Guo, Jiuli and Duchesne, Paul N. and Wang, Lu and Song, Rui and Xia, Meikun and Ulmer, Ulrich and Sun, Wei and Dong, Yuchan and Loh, Joel Y. Y. and Kherani, Nazir P. and Du, Jimin and Zhu, Baolin and Huang, Weiping and Zhang, Shoumin and Ozin, Geoffrey A.}, title = {High-Performance, Scalable, and Low-Cost Copper Hydroxyapatite for Photothermal CO2 Reduction}, series = {ACS Catalysis}, volume = {10}, journal = {ACS Catalysis}, number = {22}, publisher = {American Chemical Society (ACS)}, issn = {2155-5435}, doi = {10.1021/acscatal.0c03806}, pages = {13668 -- 13681}, year = {2020}, language = {en} } @article{NeberichOpferkuch2021, author = {Neberich, Marcel and Opferkuch, Frank}, title = {Standardizing Melanopic Effects of Ocular Light for Ecological Lighting Design of Nonresidential Buildings—An Overview of Current Legislation and Accompanying Scientific Studies}, series = {Sustainability}, volume = {13}, journal = {Sustainability}, number = {9}, publisher = {MDPI AG}, issn = {2071-1050}, doi = {10.3390/su13095131}, pages = {23}, year = {2021}, abstract = {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.}, language = {en} } @article{XiaMaoGuetal.2021, author = {Xia, Meikun and Mao, Chengliang and Gu, Alan and Tountas, Athanasios A. and Qiu, Chenyue and Wood, Thomas E. and Li, Young Feng and Ulmer, Ulrich and Xu, Yangfan and Viasus, Camilo J. and Ye, Jessica and Qian, Chenxi and Ozin, Geoffrey}, title = {Solar Urea: Towards a Sustainable Fertilizer Industry}, series = {Angewandte Chemie}, volume = {134}, journal = {Angewandte Chemie}, number = {1}, publisher = {Wiley}, issn = {0044-8249}, doi = {10.1002/ange.202110158}, pages = {6}, year = {2021}, abstract = {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.}, language = {en} } @article{HurtadoMohanUlmeretal.2022, author = {Hurtado, Lourdes and Mohan, Abhinav and Ulmer, Ulrich and Natividad, Reyna and Tountas, Athanasios A. and Sun, Wei and Wang, Lu and Kim, Boeun and Sain, Mohini M. and Ozin, Geoffrey A.}, title = {Solar CO2hydrogenation by photocatalytic foams}, series = {Chemical Engineering Journal}, volume = {435}, journal = {Chemical Engineering Journal}, publisher = {Elsevier BV}, issn = {1385-8947}, doi = {10.1016/j.cej.2022.134864}, pages = {11}, year = {2022}, abstract = {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.}, language = {en} }