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Netzwerk Nagetier-übertragene Pathogene: Monitoring von Hantavirus-Infektionen in Deutschland
(2009)
Zur Förderung einer nachhaltigeren Wertschöpfungskette werden im Rahmen der Energiewende ständig neue Verfahren und Konzepte zu deren Umsetzung entwickelt. Eines dieser Konzepte befasst sich mit der Zusammenführung bislang entkoppelter Prozessschritte in Gasreinigungssystemen aus der Energie- und Anlagentechnik. Aus den daraus resultierenden Einsparungen bei den Investitionskosten profitieren nicht nur die klassischen Energieerzeugeuer und Produktionsanlagen in der chemischen Industrie, sondern es werden auch neue Anreize zur dezentralen Energieeinspeisung von kleineren und mittelständischen Unternehmen gesetzt.
Elementarer Bestandteil dieser Gasreinigungssysteme sind häufig Elektroabscheider, welche weit verbreitet im Einsatz sind um Abgase von Stäuben bzw. Aerosolen zu befreien, oder um staubförmige Wertprodukte aus Gasströmungen abzuscheiden. Die in Elektroabscheidern prinzipbedingt vorhandenen elektro¬¬hydro¬dyna¬mischen Strömungen, auch als elektrischer Wind bezeichnet, sollen nun systematisch genutzt werden, um neben der Aerosolabscheidung gleichzeitig Aufgaben des Wärme- und Stoffaustauschs zu lösen.
Inhalte der Untersuchungen
Zur Validierung der Machbarkeit dieser neuen Techniken wurde der Einfluss des elektrischen Windes auf die turbulente Quervermischung, anhand des verbesserten Wärme- und Stofftransports, sowie des Druckverlusts im Rohrelektroabscheider getestet. Bei den Untersuchungen wurden unterschiedliche Strömungsgeschwindigkeiten, Elektrodengeometrien und Betriebsspannungen, sowie die Anwesenheit von Aerosol berücksichtigt. Ein Teil der Ergebnisse diente bereits als Validierungsgrundlage für numerische Simulationen mit einem neuartigen Turbulenzmodell [1].
[1] Medina, J., Schmidt, H., Riebel, U., Application of the one-dimensional turbulence model for electrohydrodynamic variable density flows, 17th European Turbulence Conference, 3-6 September 2019, Torino, Italy
Modeling One and Two Passive Scalar Mixing in Turbulent Jets Using One-Dimensional Turbulence
(2021)
Turbulent mixing of two passive scalars is investigated in a constant-property jets using stochastic one-dimensional turbulence (ODT). Scalars are separately injected by a central round and a surrounding annular jet that issue into a uniform co-flow of low velocity. These scalars are transported downstream and dispersed in radial direction by turbulent advection and molecular diffusion. The jet as well as the turbulent inflow are numerically simulated with ODT as stand-alone tool using a temporal (T-ODT) and spatial (S-ODT) formulation. We show that ODT captures key properties of the turbulent mixing for one scalar by performing individual scalar statistics and for two scalars by computation of joint probabilities. Some limitations of the one-dimensional modeling approach are also discussed.
Map-based stochastic modeling distinguishes molecular-diffusive from turbulent-advective transport processes in fluid flows. In the one-dimensional turbulence (ODT) model, a stochastic point process with energetically constrained rejection sampling of discrete eddy events is used to economically model the effects of turbulence on all relevant scales of the flow. Here I will discuss the model formulation and its application to passive scalar mixing in a confined jet.
[1] M. Klein, C. Zenker, H. Schmidt (2019) Chem. Eng. Sci. 204:186-202
CeOx-Cu inverse catalysts have been shown to convert CO2 into valuable chemicals through catalytic hydrogenation. The catalytic activity may further be enhanced by alloying ceria with trivalent, catalytically active metals, such as Sm, promoting the formation of Ce3+ active sites. In this work, the structural and chemical properties of (111)- and (100)- oriented CeOx islands alloyed with samarium were explored by low-energy electron microscopy and X-ray photoemission electron microscopy. After Sm deposition on the as-grown CeOx islands, the near-surface region of (100)-oriented CeOx is reduced after exposure to H2 at 470 ∘C, whereas the deeper layers as well as the whole (111)-oriented islands retain the Ce4+ state. Subsequent reoxidation with O2 leads to the complete Ce4+ state recovery, suggesting the healing of oxygen vacancies. Additional annealing at 470 ∘C induces samarium diffusion into the ceria matrix. Yet, subsequent exposure to H2 reduces neither the (111)- nor the (100)-oriented CeSmOx islands, suggesting a quite unexpected stability of this system.
The detailed numerical representation of turbulent mixing processes is a standing challenge for non-premixed chemically reacting flows. The full range of relevant flow scales needs to be captured and it is also necessary to distinguish turbulent advective from molecular diffusive processes in order to represent Reynolds and Schmidt number effects. These requirements are addressed here by utilizing two different map-based stochastic turbulence modeling strategies. The one-dimensional turbulence (ODT) model utilizes event-based turbulence modeling, whereas the hierarchical parcel-swapping (HiPS) model is a fully event-based mixing model. ODT provides full-scale resolution at affordable costs by dimensional model reduction based on the boundary-layer approximation to shear flow. HiPS is far less costly than ODT but currently limited to locally homogeneous isotropic turbulence. The physics-compatible modeling capabilities with respect to phase-space representation of turbulent mixing are demonstrated for two canonical cases using standalone model formulations.
Modeling turbulent mixing is a standing challenge for nonpremixed chemically reacting flows. Key complications arise from the requirement to capture all relevant scales of the flow and the necessity to distinguish between turbulent advective transport and molecular diffusive transport processes. In addition, anisotropic mean shear, variable advection time scales, and the coexistence of turbulent and nonturbulent regions need to be represented. The fundamental issues at stake are addressed by investigating multi-scalar mixing in a three-stream coaxial jet with a map-based stochastic one-dimensional turbulence model. ODT provides full-scale resolution at affordable costs by a radical reduction of complexity compared to high-fidelity Navier–Stokes solvers. The approach is partly justified by an application of the boundary-layer approximation, but neglects fluctuating axial pressure gradients. It is demonstrated that low-order scalar statistics are reasonably but not fully captured. Despite this shortcoming, it is shown that the model is able to reproduce experimental state-space statistics of multi-stream multi-scalar mixing. The model therefore offers physics-compatible improvements in multi-stream mixing modeling despite some fundamental limitations that remain from unjustified assumptions.
We have used low-energy electron microscopy (LEEM), micro-illumination low-energy electron diffraction (µLEED) supported by ab initio calculations, and X-ray absorption spectroscopy (XAS) to investigate in-situ and in real-time the structural properties of Sm2O3 deposits grown on Ru(0001), a rare-earth metal oxide model catalyst. Our results show that samarium oxide grows in a hexagonal A-Sm2O3 phase on Ru(0001), exhibiting a (0001) oriented-top facet and (113) side facets. Upon annealing, a structural transition from the hexagonal to cubic phase occurs, in which the Sm cations exhibit the +3 oxidation state. The unexpected initial growth in the A-Sm2O3 hexagonal phase and its gradual transition to a mixture with cubic C-Sm2O3 showcases the complexity of the system and the critical role of the substrate in the stabilization of the hexagonal phase, which was previously reported only at high pressures and temperatures for bulk samaria. Besides, these results highlight the potential interactions that Sm could have with other catalytic compounds with respect to the here gathered insights on the preparation conditions and the specific compounds with which it interacts.
Modeling complex mixing processes is a standing challenge for a number of applications ranging from chemical to mechanical and environmental engineering. Here, the gas-phase turbulent mixing in a three-stream concentric coaxial jet is investigated as a canonical problem. Reynolds-averaged Navier–Stokes simulations (RANS) suggest that the gas-phase mixing can be accurately modeled by air doped with passive scalars, for which small-scale resolving numerical simulations
are performed with the one-dimensional turbulence (ODT) model as stand-alone tool. We show that both the spatial (S-ODT) and temporal (T-ODT) model formulations yield qualitatively similar results exhibiting reasonable to good agreement with available reference experiments, Reynolds-averaged and large-eddy simulations, as well as mixing models. This is demonstrated for low-order statistics, like the scalar variance and dissipation, but also the two-scalar joint probability density functions that can not be obtained with RANS. Our results suggest that S-ODT has better capabilities than T-ODT to model the mixing processes in the jet which we attribute to the account of local advective time scales.
A new non-conforming finite element discretization methodology for second order elliptic partial differential equations involving higher order local absorbing boundary conditions in 2D and 3D is proposed. The novelty of the approach lies in the application of C⁰-continuous finite element spaces, which is the standard discretization of second order operators, to the discretization of boundary differential operators of order four and higher. For each of these boundary operators, additional terms appear on the bound-ary nodes in 2D and on the boundary edges in 3D, similarly to interior penalty discontinuous Galerkin
methods, which leads to a stable and consistent formulation. In this way, no auxiliary variables on the boundary have to be introduced and trial and test functions of higher smoothness along the boundary are not required. As a consequence, the method leads to lower computational costs for discretizations with higher order elements and is easily integrated in high-order finite element libraries. A priori h-conver-gence error estimates show that the method does not reduce the order of convergence compared to usual Dirichlet, Neumann or Robin boundary conditions if the polynomial degree on the boundary is increased simultaneously. A series of numerical experiments illustrates the utility of the method and validates the theoretical convergence results.
The epitaxial quality of thin films crucially depends on their interaction with the substrate. Up to now, Ag-terminated Si(111) has been employed as the model substrate for the growth of 3,4,9,10-perylene tetracarboxylic dianhydride
(PTCDA) on semiconductors. In this study, we will show that Bi termination results in PTCDA films of superior epitaxial quality. We have studied the growth of PTCDA on bismuth-passivated Si(111) in detail by means of spot profile analysis of low-energy electron diffraction (SPA-LEED), X-ray photoemission spectroscopy (XPS), near-edge X-ray absorptionfine structure
(NEXAFS), and scanning tunneling microscopy (STM). The XPS results reveal the presence of intact PTCDA molecules on the surface upon adsorption. NEXAFS data indicate the PTCDA molecules being oriented with their molecular plane parallel to
the surface. STM shows a very smooth growth front of the PTCDA film, preserving the step structure of the substrate. High-resolution SPA-LEED data demonstrate the presence of a multidomain surface with a rich variety of PTCDA surface structures,
which were identified to be most prominently herring-bone polytypes. However, in the monolayer range, quadratic brick-wall structures and a nearly square-like structure as well as a perylene-like structure have also been found. Despite the simultaneous
presence of multiple domains, the individual domains show excellent lateral ordering, with larger domain sizes as compared to the case of Ag-terminated Si(111).
Electrohydrodynamic‐enhanced internal pipe flows from a One‐Dimensional Turbulence perspective
(2020)
The publishers are receiving more and more inquiries about the topic “Floating Architecture”, particularly about technical details, water chemistry, as well as ice and wave problems. Since there is a lack of technical literature on this topic, most students working on projects or theses related to this topic send their inquiries. A time of general and quick changes results in a large number of daily publications. Therefore it is difficult to understand why there is a lack of lit-erature about floating structures. One has to consider that sea levels will continue to rise and consequently a larger number of people will have to live on the surface of the sea. Obviously, some expert knowledge is required which needs a longer period of time to be gained through scientific advancements and experience. The publishers, who have been dealing with the topic of floating houses for some years, are grateful to the authors for their agreement to allow the publication of their papers on floating architecture. These papers were mainly prepared for two conferences on floating architecture held in the study centre of the IBA building, Großräschen. Therefore, the reader should know that, along with the usual papers, only a selection of self-explaining transparencies is shown in order to meet the printing requirements. The included list of both the authors and their addresses makes it easy for interested people to send any inquiries to them. A short introduction as well as an outlook at the end of each paper is meant to draw attention to current events in order to be able to promptly identify opportunities and risks connected with living on the water.
Ökologische und ökonomische Bewertung von Agroforstsystemen in der landwirtschaftlichen Praxis
(2008)
Development of a Method for Multiplex Real-Time Analysis of Enzymatic Activity on a Microbead-Chip
(2013)
Development of a Method for Multiplex Real-Time Analysis of Enzymati c Activity on a Microbead-Chip.
(2013)
Micromechanical element
(2015)