1,721,029 research outputs found
Lokale Gefügeänderung von Lithium Aluminium Silikat (LAS) mittels ultrakurzer Laserpulse
No full textAlternative Ansätze und Weiterentwicklungen zum Reaktivlöten von Metall-Keramik-Verbindungen für den Einsatz in der Hochtemperatur-Brennstoffzelle
No full textThermochemische Beständigkeit von Carbonat-Keramik-Membranen für die CO-Abtrennung in Wassergas-Shift-Reaktoren
No full textThis dissertation investigates a membrane reactor consisting of an upstream water-gas shiftreaction and a CO2-permeable two-phase membrane to be used in an integrated gasification combined cycle (IGCC). This involves the reduction of CO2 emissions through a sensible use of power plant technology by means of a membrane reactor. Aim of this dissertation was to develop a material combination that is thermochemically stable under gasification conditions. This material combination was composed of a porous oxygen-ion conductor and a fluid moltencarbonate. Materialwise, the membrane consisted of a porous oxygen-ion conductor made from eitherCe0,8Gd0,2O2−d (CGO) or Ce0,8Sm0,2O2−d (SDC resp. CSO), and molten cabornate as a second phase. The chemical stability of CGO and CSO was investigated via exposure experiments and X-ray powder diffraction to ensure uniform membrane performance. Under the selected boundary conditions, both CGO and CSO were found to be chemically stable in an IGCC with and without H2S contamination. I calculated the vapor pressure of different molten carbonates using FactSage, both with and without syngas. On the basis of these calculations, the systems of Li2CO3/CaCO3 andLi2CO3/SrCO3 were closely examined. Differential thermal analysis (DTA) was used to determine the eutectic for both mixtures with an open ceramic and a closed platinum crucible. UnderCO2 atmosphere, the eutectic for 64 mol% Li2CO3/36 mol% CaCO3 was found to be 654 !C. ForLi2CO3/SrCO3, the eutectic was found to be at 25 mol% and 30 mol% SrCO3 at a melting point of 674 !C. Additionally, the combination of the two membrane phases was investigated. The hot stagemicroscope was used to analyse the penetration of Li2CO3/CaCO3 (eutec.) in CSO (1100 !C, holding time: 5 h) and CGO (1200 !C, holding time: 5 h). The element distribution in the samples was determined with energy dispersive X-ray spectroscopy (EDX). In the samples we are found CaCO3 and inhomogenously distributed Ca. Moreover Li could not be detected as it isoutside EDX’s measuring range. Finally, XRD measurements demonstrated very good chemical stability without and for200 ppm-H2S-contaminated CGO and CSO towards sulfur and each other. Furthermore, the dual gas stability measurements and EDX investigations showed high chemical stability and compatibility between catalyst and membrane. The measurement was performed with infiltrated membrane with the catalyst (86 wt.% Fe/14 wt.% Cr) in syngas. FactSage calculations and stability measurements agreed on the decomposition point of CaCO3 being not higher than800 !C. Further research investigations may lay the basis for membrane reactor improvement and will generate novel scientific findings in this research domain
Strömungsmechanische Simulation und experimentelle Validierung des kryogenen Wasserstoff-Moderators für die Europäische Spallationsneutronenquelle ESS
No full textThe European spallation neutron source ESS is currently under construction and should start part-load operation in 2023. With an average proton beam power of 5 MW, it will become the most powerful spallation neutron source worldwide. A key component of a spallation neutron source is the cold moderator. At the ESS, the cold moderator will be operated with liquid parahydrogen at a temperature and pressure around 20 K and 10 bar respectively and is intended to slow down (moderate) the fast neutrons, released by the spallation process, to the required low velocity level. Latest particle-transport-simulations show that the neutron yield can be increased by up to 30 % by optimizing the existing cold moderator. The present dissertation therefore examines the technical feasibility of this new moderator for full-load operation of the European spallation neutron source ESS. The primary goal is to verify whether the cold moderator can be operated at full proton beam power or up to which beam power a safe operation is possible. In addition, the feasibility from the structural mechanical and manufacturing point of view will be assessed. In order to investigate the flow behavior in the cold moderator, a numerical flow simulation was first carried out. The flow guiding has been optimized for the best possible heat transfer because the pulsed proton beam causes an enormous fluctuation in thermal load. Furthermore, sources of errors of the simulation were identified and minimized. For this purpose, the model error of the flow simulation was determined by particle image velocimetry (PIV) comparison measurements. As part of the parameter studies, it turned out that the cold moderator can only be safely operated up to a proton beam power of approx. 3.4 MW under the given requirements and with a conservative consideration of all errors. Therefore, a several additional options were shown, by which the proton beam power might be significantly increased, and the goal of 5 MW would still be possible. The structural mechanical part of this work, in which the cold moderator was designed according to the nuclear code RCC-MRx, showed that the pressure vessel withstands all static and dynamic loads. Thereby the radiation as well as all loads in normal and abnormal operation were considered. Finally, an initial prototype of the optimized cold moderator has been manufactured and tested. The joining technology for the selected aluminum alloy AW 6061-T6 was of special importance, since this alloy is generally difficult to weld. Electron beam welding was used because it leads to lowest possible distortions and minimized local heat input. Finally, non-destructive tests were carried out to confirm the high quality of the manufacturing, and thus the suitability of the cold moderator for a safe operation under the extreme operating conditions
Alternative Ansätze und Weiterentwicklungen zum Reaktivlöten von Metall-Keramik-Verbindungen für den Einsatz in der Hochtemperatur-Brennstoffzelle
No full textData Handling for PLC-based Research Facilities - How to Interact With Data?
No full textThe simple access to and long-term storage of measurement data at research facilities play an important role and represents an essential basis for scientific work. There are various solutions for data acquisition, such as the Experimental Physics and Industrial Control System (EPICS) Archiver or the TANGO Framework, which are particularly suitable for use with large scientific devices. For small to medium-sized Programmable Logic Controller (PLC) controlled systems, it is often not worth the effort of such a framework, so that there is often still a lot of room for improvement. This paper describes the development of a database-based acquisition system that offers the researcher easy access to the measurement data, while ensuring good usability. In addition to data storage, the system has the ability to transfer data like parameters or test routines to the PLC for execution
Theoretical optimization and experimental validation of a microchannel target for a high-current accelerator-driven neutron source
No full textThe High Brilliance neutron Source (HBS) project aims to develop a high-current accelerator-driven neutron source (Hi-CANS) to deliver high-brilliant neutron beams to a variety of neutron scattering instruments. One of the key components of such a facility is the target that generates neutrons from nuclear reactions between protons and atoms of the target material. Within the HBS project, a solid tantalum target with an innovative internal microchannel water-cooling structure was developed for a 70 MeV pulsed proton beam with a peak current of 100 mA, a duty cycle of 1.43% and an average power of 100 kW deposited on a surface area of 100 cm². Known potential risks like blistering, sufficient heat dissipation and thermomechanical stresses have been consequently tackled during the development by optimizing the neutron-producing target accordingly. The first solid tantalum target with an internal microchannel water-cooling structure was manufactured and tested with a high-power electron beam. It was shown that a power of 1 kW/cm² can be dissipated with the special microchannel cooling. In addition, a new target with an optimized microchannel structure was obtained from an iteration between particle transport simulations with FLUKA and thermomechanical simulations with ANSYS. Only 4.56% of protons accumulate in the neutron-producing tantalum and hence blistering issues are minimized. Additionally, a homogeneous heat deposition within the target was achieved minimizing strains and stresses. Steady-state and transient analysis on the cooling effect of the target in operation shows that the maximum temperature and heat flux could be kept in a safe range with the proposed microchannel structure. A prototype of the optimized target was manufactured via wire erosion and the tolerances were examined successfully with computed tomography. The maximum machining error is 0.2 mm and the effect on the target’s lifetime is negligible, proving the optimized microchannel target is manufacturable and reliable
Auslegung einer Lager- und Antriebseinheit für ein neuartiges Röntgentarget zur Strahlentherapie
No full textCancer is one of the major health problems in Europe and leads to enormous socioeconomic burdens. In 2019, 1.55 million people in the EU died from cancer, and 50\% of all cancer patients receive radiotherapy during the course of their disease. Microbeam radiation therapy is a promising approach to successfully minimize the damage to healthy tissue. Preclinical research with MST only became possible with the advent of large synchrotron facilities in the 1990s. However, these costly research facilities are unsuitable for widespread use in the healthcare system, leaving an unmet need for compact sources of microbeam therapy. The core of this work is the design and construction of a bearing and drive unit of a novel x-ray target for a compact microbeam source prototype. In addition to the historical development of x-ray sources, a principal design system is described in which the three bearing variants: rolling bearings, magnetic bearings and sliding bearings are compared on the basis of their technical characteristrics. The principle of a liquid metal lubricated plain bearing provided the best compromise with respect to the given requirements. For the design of the bearing system, the state of the art is analyzed based on a literature review. The relevant fundamentals for modeling the bearing, taking turbulence and cavitation into account, are presented. A recalculation and comparison with other models from the literature is carried out using numerical methods and an analytical solution of the pressure distribution. Based on this, the optimized parameters for the bearing of the rotating anode are calculated. In addition, the influences of frictional heat, manufacturing aspects of the bearing and corrosion due to the liquid metal are discussed and preventive measures are taken. With the bearing calculation completed, the design, construction and calculation of the drive train with target connection is carried out, which consists of two rotating rotor carriers running concentrically around a stationary axis. The liquid metal bearing is formed between the axis and the rotating anode. An asynchronous machine with a separation tube as vacuum boundary drives the rotor. As part of a preliminary test, the behaviour of the liquid metal when it is filled into a vacuum chamber is investigated. For the overall system integration, which consists of a total of 4635 individual parts, the construction and assembly within a radiation protection cabinet is considered and the boundary conditions are planned and carried out
Entwicklung glasbasierter Dichtungsmaterialien für das Fügen von Sauerstofftransportmembranen
No full textIn this thesis, different glass-based sealants were developed for joining oxygen transport membranes (OTM) to obtain matching the coefficient of thermal expansion (CTE) with membrane and support metals. The crystallization behavior of the BaO–CaO–SiO2–B2O3 system glass (H) and BaO–SrO–SiO2–B2O3 system glasses (BS) will be discussed. In addition, the glass-forming stability of glass matrices, filler type and amount effect on CTE, chemical compatibility, mechanical strength, shrinking behavior, viscous flow property, joining behavior, thermal cycling and long-term thermal stability were analyzed for various glass-based sealants. The feasibility of the fast joining process was also investigated to economize the energy costs of the heating process. SrTi0.75Fe0.25O3-δ (STF25) was used as an OTM, and the sealing partners were ferritic steel Aluchrom, pre-oxidized Aluchrom and Crofer22APU.BaO–CaO–SiO2–B2O3 system glass H matrix was first investigated with respect to its glass-forming tendency, crystallization and CTE. The crystalline behavior of glass H as the sealant matrix was investigated and predicted by experimental X-ray diffraction (XRD) analysis and the simulation using the thermodynamic package FactSage. Glass H exhibits a relatively low CTE (9.6 × 10-6 K-1) compared to STF25 and Aluchrom. Nine different filler materials were added to glass H in various amount for improving the CTE of glass-based composite sealants. Dilatometric tests were carried out to observe the influence of filler on thermal expansion. The viscous flow behavior of the composite sealant was investigated by hot stage microscopy (HSM) to determine the optimal joining temperature. The joining behavior of glass-based sealants for different thermal joining processes were analyzed via helium leakage testing, X-ray computed tomography (CT) inspection, scanning electron microscopy (SEM) analysis on cross-sections of the joints. The joints showed low helium leak rates smaller than 10-9 mbar·l·s-1 and good adherence of the glass sealants to the support metals and STF25. The mechanical shear strengths of sealants were measured by torsion testing on hourglass-shaped samples. A higher shear stress up to 62.2 MPa was found on composite joint which 40 wt.% Ag (HAg40) was added. HAg40 was able to withstand 20 times thermal cycles between room temperature and 800 °C and exhibited good thermal stability at 800 °C for up to 1500 h. These glass H-based sealants are promising candidates for OTMs.Three new BaO–SrO–SiO2–B2O3 (BS) glass sealants with different SrO contents (6-25 mol%) were developed for OTM joining applications. The strontium content was investigated in terms of its effect on the glass-forming tendency, thermal expansion, crystallization, shrinkage behavior, viscous flow, and joining behavior. The CTE value decreases with the increasing SrO content of the BS glasses. The glass with 15 mol% (BS15) SrO produced the best matching CTE (11.9 × 10-6 K-1) with STF25 and Aluchrom. The crystallization behavior of the BS glasses was investigated by XRD. Sinking dilatometric measurements simulated the joining procedure and observed the shrinkage behavior of the BS glasses. The viscous flow behavior of the BS glasses was investigated via HSM. The optimal joining temperature of the BS15 glass was chosen close at half-ball temperature. The sandwiched sample sealed by the BS15 glass achieved good gas-tightness with a low helium leak rate of < 10-9 mbar·l·s-1
Auswirkungen von Kohlenstoffmonoxid auf den Betrieb katalytischer Wasserstoffrekombinatoren in Leichtwasserreaktor-Sicherheitsbehältern
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