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Semi-solid metal alloys, as used in industrial thixoforming, have a special microstructure of globular grains suspended in a liquid metal matrix. The complex rheological properties are strongly influenced by the local solid fraction, particle shape, particle size and state of agglomeration. It was analysed how the microstructure develops in dependence of the shear rate and cooling rate during the solidification and it was observed that the average particle size increased with increasing shear rate and decreasing cooling rate. In order to account for those phenomena, the rate of crystal growth and the relationship between average particle diameter and viscosity was modelled by applying the Sherwood two-film model for the mass transport. The dependence of the viscosity from the particle size were modelled with a modified Krieger–Dougherty model. Based on the rheological and microstructural observations an evaluation method was elaborated that allows for the construction of objective master curves that are independent of the particle growth during the experimentation. The isothermal experiments for the characterisation of the rheological behaviour consisted of step-change of shear-rate and yield-stress experiments. From the experimental data the steady-state flow curves could be determined as well as the time-dependent relaxation of the shear stress after a change of shear rate. The steady-state rheological behaviour was found to be shear thinning. Nevertheless, immediately after a shear-rate change an overshoot was observed that resulted from a short-time shear-thickening behaviour. The yield stress was found to strongly depend on the microstructure and the degree of agglomeration of the solid phase. With increasing rest time the yield stress was increasing strongly, because of the agglomeration of the solid particles. Based on the step-change of shear-rate experiments a single-phase flow has been developed that consists of a modified Herschel–Bulkley approach and accounts for the thixotropic as well as for the yield-stress behaviour of the alloys.
Semi-solid metal alloys, as used in thixoforming, have a special microstructure of globular grains suspended in a liquid metal matrix. The complex rheological properties are strongly influenced by the local solid fraction, particle shape, particle size and state of agglomeration. There is a high demand for models and software tools allowing the simulation of semi-solid casting processes. The material under investigation is a tin-lead alloy (Sn-15%Pb) which exhibits a similar microstructure to aluminium alloys. The experiments were performed with a concentric cylinder rheometer of the Searle type. Initially, the liquid alloy is cooled down to the semi-solid range under constant shearing and then kept under isothermal conditions for further experimentation. Based on the experimental data, a single-phase model has been derived where the semi-solid alloy is regarded as a homogeneous material with thixotropic properties and the microstructure is characterised by a structural parameter. The model consists of two parts: the equation of state, including a finite yield stress, and a rate equation for the structural parameter. The model equations are employed in numerical software and used for the simulation of characteristic filling cases and the comparison with the conventional filling.
Semi-solid metal alloys, as used in thixoforming, have a special microstructure of globular grains suspended in a liquid metal matrix. The material under investigation is a tin–lead alloy (Sn–15% Pb) which exhibits a similar microstructure as aluminum alloys. The experiments were performed with concentric cylinder rheometers. Initially, the liquid alloy is cooled down to the semi-solid range under constant shearing and then kept under isothermal conditions for further experimentation. The microstructure is characterized in dependence of the shearing time. The rheological techniques consisted of step change of shear rate and shear stress ramp experiments for different solid fractions (40–50%). Based on the experimental data a single phase model has been derived, where the semi-solid alloy is regarded as a homogeneous material with thixotropic properties and the microstructure is characterized by a structural parameter. The model consists of two parts: the equation of state, including a finite yield stress, and a rate equation for the structural parameter. The model equations are employed into numerical software and used for the simulation of a characteristic thixocasting process. The results are compared to real experiments.
The deployment of containers as building modules has grown in popularity over the past years due to their inherent strength, modular construction, and relatively low cost. The upcycled container architecture is being accepted since it is more eco-friendly than using the traditional building materials with intensive carbon footprint. Moreover, owing to the unquestionable urgency of climate change, existing climate-adaptive design strategies may no longer respond effectively as they are supposed to work in the previous passive design. Therefore, this paper explores the conceptual design for an upcycled shipping container building, which is designed as a carbon-smart modular living solution to a single family house under three design scenarios, related to cold, temperate, and hot–humid climatic zones, respectively. The extra feature of future climate adaption has been added by assessing the projected future climate data with the ASHRAE Standard 55 and Current Handbook of Fundamentals Comfort Model. Compared with the conventional design, Rome would gradually face more failures in conventional climate-adaptive design measures in the coming 60 years, as the growing trends in both cooling and dehumidification demand. Consequently, the appropriate utilization of internal heat gains are proposed to be the most promising measure, followed by the measure of windows sun shading and passive solar direct gain by using low mass, in the upcoming future in Rome. Future climate projection further shows different results in Berlin and Stockholm, where the special attention is around the occasional overheating risk towards the design goal of future thermal comfort.
Hintergrund: Im Zuge der weltweiten Flüchtlingsbewegungen ist in den letzten Jahren eine hohe Anzahl an geflüchteten Personen nach Deutschland gekommen. Laut amtlicher Statistik lebten Ende 2018 ca. 1.780.000 Schutzsuchende in Deutschland (Statistisches Bundesamt 2019). Der Anteil weiblicher Schutzsuchender beträgt ca. 37,4 Prozent. Zirka 51 Prozent der geflüchteten Frauen, die in Deutschland ankommen und Asyl beantragen, befinden sich im gebärfähigen Alter zwischen 15 und 45 Jahren (Statistisches Bundesamt 2019a; _b). Darüber, wie viele schutzsuchende Frauen schwanger eingereist sind oder zum Zeitpunkt ihres Aufenthaltes in der Erstaufnahmeeinrichtung schwanger geworden sind, liegen keine Daten vor. Ebenso fehlen bisher in Deutschland repräsentative gesundheitsbezogene Daten von Schutzsuchenden (Frank, Yesil-Jürgens & Razum et al. 2017). Insbesondere zu den gesundheitlichen Problemlagen und Bedürfnissen von schutzsuchenden Frauen im Bereich Schwangerschaft, Geburt und postpartaler Phase liegen keine Erkenntnisse vor (Bozorgmehr, Mohsenpour & Saure et al. 2016; Heslehurst, Brown & Pemu et al. 2018). Internationale Studien deuten allerdings darauf hin, dass die gesundheitsbezogene Bedarfslage schutzsuchender Frauen komplex ist (Gagnon, Zimbeck & Zeitlin et al. 2009;van den Akker & van Roosmalen 2016). Die systematische Identifizierung von Versorgungsbedarfen und eine bedarfsgerechte Versorgungsplanung sind deshalb derzeit kaum möglich (Mörath 2019). Aus rechtlicher Perspektive ist diese unbefriedigende Situation ebenfalls problematisch (Klotz 2018). Die Umsetzung des völkerrechtlich bindenden internationalen Rechts auf ein für sie [Anmerk. d. V. : die Person] erreichbares Höchstmaß an körperlicher und geistiger Gesundheit (BGBI. 1976), welches von Deutschland 1976 ratifiziert wurde, sowie des UN-Übereinkommens zur Beseitigung jeder Diskriminierung der Frau von 1979 (BGBI. 1985) und der in der EU-Richtlinie 2013/33/EU in Kapitel IV aufgeführten Bestimmungen für schutzbedürftige Personen erfordert für diese spezifische Personengruppe vielfache Bemühungen. Denn die Förderung und Verbesserung der sexuellen und reproduktiven Gesundheit bzw. Rechte von schutzsuchenden Frauen kann einen Beitrag zu ihrer gesellschaftlichen Integration nach sich ziehen (Janssens, Bosmans & Temmerman 2005). Zuzüglich zur rechtlichen Situation schutzsuchender Frauen gilt das Recht ihrer Kinder auf Gesundheit. Im Artikel 24 der UN-Kinderrechtskonvention (UN, Committee on the Rights of the Child 2013) ist dieses verankert und unterstreicht u. a. für die Vor- und Nachsorge relevante Versorgungsbereiche wie z. B. prä- und postnatale Versorgung der Mütter, Aufklärung über Gesundheit und Ernährung u. w. m. (Deutsches Institut für Menschenrechte 2017).
Making solar thermal systems less expensive, often results in a lower system efficiency. However, the cost-benefit ratio is relevant from the perspective of the consumer. The complex impact of component-related and system-related design parameters on the economics of a complete system makes the evaluation and economical optimization difficult.
Therefore, a complete simulation environment has been developed, which can automatically optimize solar-thermal systems,including collector and system parameters. The main collector module consists of a one-dimensional thermal model that was validated with a commercial solar collector. The efficiency curve and the production cost werecalculated as a function of several design and construction parameters. The collector module was linked to the commercial software Polysun®, so that parametric studies can be performed with minimaleffort. Optimization problems can be solved by using the Matlab® optimization toolbox.
The simulation environment wasused for sensitivity studies and optimization problems in order to analyze the impact of collector design-parameters with respect to system cost, system yield andeconomic values. We will demonstrate how a collector can be optimized and how the ideal system parameters like collector number and storage volume can be easily calculated. Finally, we will show how the optimizer is used for a given system in order to find ideal values for the absorber-sheet thickness and the number of pipes. Due to the holistic approach, the application of this tool set can be used for collector development as well as for system planning.
Die Auswahl einer geeigneten Forschungsmethode hängt von der Forschungsfrage, den TeilnehmerInnen einer Studie und von den angestrebten Daten ab. Sie ist die zentrale Voraussetzung für einen gelingenden Forschungsprozess. Wie eine Methodenentscheidung im Verlauf eines Forschungsprojektes getroffen wird, zeigt das Beispiel einer Befragung von Hebammen und Pflegenden in der Familiengesundheitsversorgung.