Manfred Greger

Thermophilic digestion of cellulose at high-organic loading rates

The influence of high punctual organic loadings on performance of anaerobic biocenosis was examined. Thermophilic batch series with microcrystalline cellulose at six organic loading rates (OLRs) were performed (5.7–34.3 kg VS/m3). With the loading increase and exceeding of recommended substrate/inoculum ratio of 0.5 for volatile solids, an inhibitory state was targeted. Although extreme OLRs had been applied, they did not lead to the permanent acidosis. The only explicit sign of system stress was the increasing total degradation time and the extended period of higher biogas production rate with every increase of OLR. Measured fermentation parameters (pH, oxidation–reduction potential, volatile acids and acids/buffer capacity ratio) were changed simultaneously during fermentation. A clear system evaluation was not possible with any of these parameters without gas production. This confirms gas production as the first and most important control parameter for the supervision of the fermenting process. Also, propionic/acetic acid ratio as well as C4‐C5 fatty acids delivered only ambiguous results. Even significant exceeding of limits given by the literature did not result in extreme system performance. The observed signs of system stress were not proportional to the applied OLRs. They resulted from hydrolysis or acetogenesis rate delay. In addition, they prove a much higher than expected adaptation level of microbial biocenosis to increasing OLR if the loads are introduced gradually.

Thermal and electrical aging of laser braze-welded aluminum–copper interconnects

Aluminum–copper (Al–Cu) interconnects are of great interest for a variety of electrical applications, such as lithium-ion batteries. In this paper, the effects of thermal and electrical aging on the intermetallic compound growth of laser braze-welded Al–Cu interconnects are reported. Thermal aging was studied in a temperature range from 200 to 500 °C for durations between 1 and 120 h. Electrical aging was studied with 200 A direct current application with different polarities and durations between 1 and 24 h. The formation of intermetallic compounds was found to be dependent on the type of aging and, for electrical aging, on the polarity of the current. The growth of intermetallic compounds under the influence of the electric current was distinctly higher than for thermal annealing conditions. The formation of voids at the transition between intermetallic compounds indicates that electromigration may be the main driving force for the accelerated intermetallic growth.

Überarbeitete Methode zur hydraulischen Berechnung von Stabrechen

Der hydraulische Verlust von Feinrechenanlagen wird sehr oft uber die Berechnungsmethode nach Kirschmer ermittelt. Vergleiche der Berechnungsergebnisse mit realen Messwerten ergaben Differenzen. Die bekannte Formel wurde erweitert und evaluiert.

Schwingfestigkeit von Leichtbauplatten mit Wabenkernstruktur.

Kurzfassung Leichtbauplatten mit Deckschichten aus Aluminium und Aluminiumwabenkern wurden in zyklischen Vierpunktbiegeversuchen getestet. Dabei wurden in Folge konstanter und variabler Lastamplituden Wöhler- und Gaßnerlinien ermittelt. Die Versuche erfolgten mit zwei verschiedenen Plattenkonfigurationen, wobei der Unterschied in der Orientierung des Wabenkerns lag. Als Versagensbild waren lediglich Risse im Deckblech im Bereich reiner Biegung zu beobachten. Um eine rechnerische Vorhersage der Lebensdauer von Bauteilen zu ermöglichen, wurde ein Finite-Elemente-Modell mit homogenisiertem Wabenkern entwickelt. Unter Zuhilfenahme der aus den Vierpunktbiegeversuchen ermittelten Wöhler- und Gaßnerlinien können mit diesem FE-Modell Lebensdauern berechnet werden, wobei zunächst eine Aussage bzgl. der Deckbleche möglich ist.