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Für Fernwärmeversorger spielt die Lastprognose bei der Anlageneinsatzplanung eine zentrale Rolle. Benötigte Fernwärme oder auch -kälte lassen sich umso kostengünstiger, effizienter und emissionsärmer bereitstellen, je exakter die zu erwartende Last abgeschätzt werden kann. Ein neuartiges, an der Hochschule Kempten entwickeltes Verfahren namens »Deep DHC« kann die Genauigkeit dieser Lastprognosen deutlich erhöhen
Using scanning transmission X-ray microscopy combined with X-ray magnetic circular dichroism, element-specific hysteresis loops with a 25 nm X-ray probe are obtained on 35 nm Fe/Gd multilayer nanoislands fabricated by extreme ultra-violet interference lithography. Local hysteresis loops measured for the individual islands and the antidot film between the islands display similar behavior resulting from the lateral confinement. Line scan measurements confirm ferrimagnetic coupling between Fe and Gd in the patterned region. The ability to measure magnetization reversal with X-rays at high spatial resolution will provide an important tool for future characterization of sub-50 nm nanostructures.
Group III nitrides are promising materials for light emitting diodes (LEDs). The occurrence of structural defects strongly affects the efficiency of these LEDs. We investigate the optical properties of basal plane stacking faults (BFSs), and the assignment of specific spectral features to distinct defect types by direct correlation of localized emission bands measured by cathodoluminescence in a scanning electron microscope with defects found in high resolution (scanning) transmission electron microscopy and electron beam induced current at identical sample spots. Thus, we are able to model the electronic structure of BSFs addressing I-1, I-2, and E type BSFs in GaN and AlGaN with low Al content. We find hints that BSFs in semipolar AlGaN layers cause local changes of the Al content, which strongly affects the usability of AlGaN as an electron blocking layer in nitride based LEDs.
The implementation of friction crush welding (FCW) offers a versatile application in the welding of sheet metals. Three materials (EN AW 5754H22, DC01 and Cu-DHP) were analysed by applying the method with flanged edges. The additional material required to form the weld is provided by the flanged edges of the parent sheet metal. The joint is formed by the relative motion between a rotating disc, which is applied with a crushing force, and two sheet metal parts. The fundamental process variables and the requirements of the welding preparation are shown. Bond strengths, as a percentage of the yield strength of the parent material, of around 95% (DC01) 90% (EN AW 5754H22) and 62% (Cu-DHP) are achieved. Microstructural investigations reveal that a dynamic solid-state deformation and recrystallization of the additional flanged material results in a fine grain microstructure in the weld region. Reduced metallurgical changes along with minimized distortion and residual stresses in the parent material indicate low heat input. By creating a fine grain microstructure in the welding line, the friction crush welding method reveals great potential, especially for welding steel.
For further optimization of the automotive power train of diesel engines, advanced combustion processes require a highly flexible injection system, provided e. g. by the common rail (CR) injection technique. In the past, the feasibility to implement injection nozzle volumetric flow sensors based on the thermo-resistive measurement principle has been demonstrated up to injection pressures of 135 MPa (1350 bar). To evaluate the transient behaviour of the system-integrated flow sensors as well as an injection amount indicator used as a reference method, hydraulic simulations on the system level are performed for a CR injection system. Experimentally determined injection timings were found to be in good agreement with calculated values, especially for the novel sensing element which is directly implemented into the hydraulic system. For the first time pressure oscillations occurring after termination of the injection pulse, predicted theoretically, could be verified directly in the nozzle. In addition, the injected amount of fuel is monitored with the highest resolution ever reported in the literature.
The relative humidity level in the immediate vicinity of objects such as foods and technical items has an influence on transpiration and undesired relative humidity dependent reactions on their surfaces such as water vapour condensation, chemical reactions and microbial growth. Desirable are therefore materials that regulate the relative humidity to predefined levels in closed spaces such as in packagings and also in housing spaces. Such materials should be able to adjust the surface humidity of objects via water vapour diffusion in the gas phase without being in direct contact. A strategy to create such humidity regulating materials is the use of substances that absorb and desorb high amounts of water vapour, such as sodium chloride. Sodium chloride (NaCl) particles absorb water vapour at a relative humidity above 75% at 23 degrees C and then they form NaCl solution. NaCl solution desorbs water vapour when the relative humidity in the immediate vicinity decreases below the equilibrium relative humidity of that salt solution. Therefore, this system is able to regulate the relative humidity in its immediate vicinity. A strategy to provide free space in polymeric structures for the NaCl solution is the creation of cavities by foaming and stretching. However, only little knowledge exists about the influence of the combination of both processes on the functional properties of humidity regulating films with salt as active substance. Hence, the aim of this study was to investigate how and to which extend foaming and/or stretching affects the functional properties, i.e. water vapour sorption and mechanical properties, of polypropylene (PP) films containing NaCl particles. For this study, foamed and non-foamed PP with 3 and 6 weight-% NaCl were extruded into films. In the next step, some of these samples were biaxially stretched and their structures, water vapour absorption, porosities and mechanical strengths were analysed. The only-foamed films had a porosity of 0.3, the porosity of only-biaxially stretched films was between 0.1 and 0.2. The porosity increased to 0.7 when the films were first foamed and stretched afterward. Foamed and then stretched films with 6 wt.-% NaCl absorbed a high amount of water vapour from air with a value of 0.8 g H2O/g film at 97% relative humidity. Stretching of filled and non-filled foamed films also resulted in higher mechanical strength of the pure matrix polymer in comparison to the pure matrix polymer of non-stretched films. By the results of this study is shown that humidity regulating films with high water vapour sorption capacity can be produced via extrusion, foaming and stretching processes which are established processes in the polymer industry.
Natural gas-fueled combined cycle (NGCC) allows to reach the best performance among power plants fed by fossil fuels, but causes considerable CO2 emissions. With the aim of reducing greenhouse gases impact, NGCC could be integrated with post-combustion CO2 removal systems, typically based on chemical solvents like amines, that cause very large net efficiency penalties (about 9-12 percentage points at 90% overall CO2 capture). To reduce these high capture penalties, exhaust gas recirculation (EGR) has been studied. To further enhance the overall plant efficiency, the recovery of available low temperature heat from the solvent-based CO2 removal systems could be also performed. Low temperature heat is available in flue gas coolers (80-100 degrees C), in the amine reboiler water cooling (130-140 degrees C) and in the splitter condenser (100-130 degrees C). This waste thermal energy could be recovered by means of an Organic Rankine Cycle (ORC) that is able to convert heat into electricity efficiently even at comparably low temperatures. N-Butane was found to be as the most promising organic working fluid for the cycle operating temperatures and pressures. ORC produces additional electrical power improving the global performance of the power plant, for example, up to 1-1.5 percentage points in efficiency.
Polymers with dispersed desiccants are relevant for various packaging applications to protect packaged goods from water vapor. The intention of this study was to analyze and to describe a relevant system. Therefore, films with calcium oxide (CaO) were investigated, because such materials are hardly described in scientific literature. Monolayer films with 0.14 to 0.51 g dispersed CaO per 1 g film (PE-LD) were prepared and they absorbed up to 0.2 g water vapor per 1 g of film. The water vapor absorption was described by effective diffusion coefficients. By the use of effective diffusion coefficients and the absorption capacity, the absorption behavior of layers with various thicknesses can be estimated. The steady state (effective) water vapor permeation coefficients of the films with dispersed CaO were a factor of 2 to 24 (8.4 to 101.5 mg cm [cm(2) s Pa](-1) x 10(12), at 23 degrees C) higher than for pure PE-LD films (4.26 mg cm [cm(2) s Pa](-1) x 10(12), 23 degrees C). The tensile stress changed only slightly (pure PE-LD: 9.5 N mm(-2); PE-LD with 0.14 g dispersed CaO per 1 g film: 8.1 N mm(-2); PE-LD with 0.51 g dispersed CaO per 1 g film: 10.5 N mm(-2)), while the tensile strain at break was reduced with higher CaO concentration from 318% (pure PE-LD) to 10% (PE-LD with 0.51 g dispersed CaO per 1 g film). (c) 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47460.