Insulating polymeric foams have an important role to play in increasing energy efficiency and therefore contributing to combating climate change. Their development in recent years has been driven towards the reduction of thermal conductivity and achievement of the required mechanical properties as main targets towards sustainability. This perception of sustainability has overseen the choice of raw materials, which are often toxic, or has placed research efforts on optimizing one constituent while the other necessary reactants remain hazardous. The transition to the circular economy requires a holistic understanding of sustainability and a shift in design methodology and the resulting research focus. This paper identifies research needs and possible strategies for polymeric foam development compatible with Circular Product Design and Green Engineering, based on an extensive literature review. Identified research needs include material characterization of a broader spectrum of polymer melt–gas solutions, ageing behavior, tailoring of the polymer chains, detailed understanding and modeling of the effects of shear on cell nucleation, and the upscaling of processing tools allowing for high and defined pressure drop rates.
Fernwärmeleitungen werden durch erhebliche Temperaturwechsel beansprucht und interagieren deshalb bei der üblichen Erdverlegung intensiv mit dem umgebenden Boden, der die temperaturinduzierte Verformung behindert. Die axiale Verformung der Leitung mobilisiert Reibungskräfte und die laterale Verformung z. B. in Bogenbereichen Bettungswiderstände. Beide Bodenwiderstände verändern sich mit der Betriebsdauer der Leitung infolge ihrer Zyklenabhängigkeit. Die mobilisierbare Reibungskraft ist überdies von der Betriebstemperatur der Leitung abhängig, sodass sich ein sehr komplexes Tragverhalten ergibt, das in der derzeitigen Bemessungspraxis nur stark vereinfacht erfasst wird. Der vorliegende Fachaufsatz stellt den Kenntnisstand bezüglich der Reibungskräfte und Bettungswiderstände zusammengefasst dar und beschreibt den in einem laufenden Forschungsprojekt verfolgten Ansatz zur genaueren Erfassung des Tragverhaltens erdverlegter Fernwärmeleitungen.
The earth pressure acting on buried pipes is decisive for the pipe design. For pipes shifting in the ground, such as district heating pipes, which are subjected to cyclic temperature loading, the mobilizable friction force, which is also dependent on the earth pressure load, is a very important quantity. Friction force changes with cyclic axial displacement of a pipeline in operation. A special testing device was designed to investigate the friction forces and the normal pressures on a pipe buried in sand and how these change during cyclic axial displacement dependent on system and soil parameters. The experimental setup is presented, and in particular the application of the tactile pressure sensor, the special measuring technique used, is described. The dependence of the decrease in friction force on pipe diameter, soil overburden height, and relative density of the soil was investigated in the tests. The results are presented and the findings are discussed.
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