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Im 21. Jahrhundert haben einige Länder als Reaktion auf die Nuklearkatastrophe von Fukushima bereits den Ausstieg aus der Kernkraft beschlossen oder zumindest in Erwägung gezogen. Das Ende der Kohleverstromung ist in einigen Ländern bereits umgesetzt oder wie in Deutschland für 2038 zumindest beschlossen, um den globalen Klimawandel zu verlangsamen. Es stellt sich also die Frage, ob die „Dampfmaschine“, das heißt der Rankine-Kreisprozess noch eine Zukunft hat?

Entgegen dem aktuellen Trend, Abwärme im kleinen Leistungsbereich unter 100 kW(el.) mittels einer ORC-Anlage in Strom umzuwandeln, wird im vorliegenden Beitrag das Konzept eines Mikro-Dampfkraftwerks verfolgt. Nachfolgend wird erläutert, warum die Wahl der Turbine auf eine geschwindigkeitsgestufte zweikränzige Curtis-Turbine gefallen ist und das dafür verwendete 1-D-Turbinendesign-Tool wird kurz vorgestellt. Der parametrisierte Ansatz des Turbinenentwurfs in 3-D-CAD/CFD wird erläutert und schließlich werden das CFD-Strömungsfeld und die Leistungskennfelder der entworfenen Turbine diskutiert.

Introduction: We aimed to examine whether student teachers’ tendency to test anxiety relates to their later perspective-taking tendency and self-efficacy. The purpose of the presented study was to obtain first insights into the relationship between test anxiety, perspective-taking, and self-efficacy tendencies in student teachers. These tendencies may determine student orientation across different situations. We tested the hypothesis that the test anxiety components emotionality and worry relate to later low perspective-taking and self-efficacy. Methods: We conducted a longitudinal study with 275 student-teachers and analyzed the obtained data using structural equation modeling. Results: The data analysis revealed that only emotionality is related to lower perspective-taking and self-efficacy in later life. Discussion: We conclude that lowering student teachers’ test anxiety emotionality (e.g. through interventions) would result to later increased perspective-taking tendency. Limitations: Participants attended the study voluntarily, so it was a self-selected sample. We employed a correlational design over two measurement times instead of experimental methods. Conclusions: The obtained results give an explanation of why student teachers focused rather on themselves than on school students in classes. The perspective-taking tendency is important for teachers’ student orientation. The role of perspective-taking in different teaching situations might be investigated in further research.

Waste Heat Recovery at industrial processes becomes more and more important. The thermal profiles in these processes undergo high fluctuations, which pose a problem for downstream Organic Rankine Cycles. A possibility to cope with this circumstance is the implementation of storages or intermediate cycles, but in this paper, a different approach is followed. The ORC conditions should be kept constant by means of an adaptable turbine geometry. The present publication deals with the investigation of two different technologies to adjust the swallowing capacity of a cantilever ORC turbine - rotatable nozzle ring (RNR) and adjustable nozzle height (ANH). The considerations were performed on a reference turbine using pressurized air as working fluid. But a transfer of the findings to ORC application is reasonable. By performing comprehensive CFO analysis of the two technologies, the ANH technology was found to be superior. This is why a prototype of this technology was built and tested on a pressurized air test rig. Only small deteriorations of the total-to-static turbine efficiency at 50% design mass flow rate were observed. Based on this result, a ORC prototype of the ANH technology will be tested in future.

Development of micro ORC systems with 1-15 kW power output for micro-cogeneration and waste heat recovery at the Czech Technical University in Prague, University Centre for Energy Efficient Buildings (CTU UCEEB) has over ten years of history with many successes. These include 6 different ORC units, all with in-house designed rotary vane expanders (RVE) of many versions throughout this development. Among main advantages of the RVE belong relatively simple and robust design at low cost even at very small series of single-unit production and all that with acceptable efficiency. The ORC units operate with hexamethyldisiloxane (MM) working fluid at high pressure ratios and expansion ratios and the isentropic efficiency of RVE has a limit at these conditions around 60%, often however only at values around 50%. While this might be enough on a cost side for commercialization of this technology, in pursuit of higher efficiency solutions, different expander technology needs to be selected. A turbo-expander is a logical choice with prospect of higher efficiency. At the same time, a literature review has found a lack of reported detailed experimental data for micro (5-50 kW) turbo-expanders, possibly hindering global development towards economically feasible solutions. A project named Dexpand, “Optimised expanders for small-scale distributed energy systems” aims at these issues by objectives in designing, optimizing, manufacturing and testing several ORC expanders with MM and isobutane and their subsequent performance mapping and comparison. One major task is a design of a turboexpander for a 120 kWth biomass fired microcogeneration ORC unit currently operated at the CTU UCEEB. An axial impulse single stage turboexpander was selected as a suitable choice, providing a prospect of a decent efficiency at technically manageable rotational speed and size. This paper provides a detail of currently performed design activities, starting from boundary conditions specification, over development and optimization of a 1D model, preliminary 2D CFD calculations and finishing in a state of a robust and detailed 3D CFD model with a real gas model. Note that the working fluid, high molar mass organic vapour, is highly non-ideal in its behaviour and the flow conditions with pressure design ratio around 13 is highly supersonic (nozzle outlet isentropic Mach number exceeds 2). The current results based on 3D CFD indicate a prospect of an isentropic efficiency 71% at mechanical power output of 11 kW. Lastly, ongoing and future work is outlined, which includes aerodynamic optimization based on the developed 3D CFD model and construction design of the entire turbine assembly.

In order to meet the targets set out in the Paris climate agreement of 2015, the energy sector needs to be restructured. In Germany for example the goal is to move out of both nuclear and coal-fired power. In order to fulfil more demanding energy requests alternative sources of energy must be found and made available. One component is the usage of Waste Heat Recovery. This paper deals with the evaluation simulation of an Elektra turbine, which concept is a velocity compounded radial re-entry single wheel turbine. Based on the first turbine design, multiple simulations were carried out in order to maximize the efficiency. With these simulations, optimization opportunities are described and identified. The paper concludes with a comparison of the results achieved by numerical simulation and on the experimental test bench. The main focus for this paper is to analyze the actual flow phenomena to identify possibilities for further improvements. All simulations were calculated with the commercial software FINETM/TURBO 15.1.

The paper deals with the CFD simulation and investigation of an axial Micro-ORC-Turbine, running with the working fluid hexamethyldisiloxane (MM). The CFD results are compared to the experimental results of the turbine, which were determined at the Center of Energy Technology at the University of Bayreuth. The simulation software Fine/Turbo by NUMECA was used for the meshing and simulation of the turbine. After the mesh studys and optimization of the geometry grid have been carried out, different pressure ratios and rotational speeds have been simulated. The simulated efficiency maps were compared to the experimentally determined efficiency maps. The simulated efficiency characteristics show principally a very similar turbine operating behavior to the measured ones. However, the simulated efficiencies are about 2 to 3 percentage points higher than the measured data. Through the detailed analysis of the blade-to-blade flow fields, it was possible to plausibly trace the integral course of the efficiency curves. Thus, CFD turbine flow simulation proved to be a valuable tool to predict the efficiency characteristics of a Micro-ORC-Turbine.

Due to the various ORC applications, it is not expedient to design and build one standard turbogenerator. Therefore, authors developed a flexible “micro-turbine-generator-construction-kit (MTG-c-kit)” by means of which a customized turbogenerator can be made for any required power output between 1 and 200 kW, for a wide range of working fluids and boundary conditions – quickly, cost effectively and with high expander efficiency. The architecture and main features of this kit are briefly introduced. However, more focus is put on the developed 1D turbine design tool. It allows to quickly design and optimize a single stage turbine for any fluid and boundary conditions. The implemented models are presented on two specific design examples - an axial impulse and a radial inflow cantilever turbine. Also, the experimental results of the two micro turbines designed and built according to this approach, are presented and discussed. Focusing to further accelerate and cheapen the customized micro-turbogenerators for low temperature applications, we provide an outlook of possibilities of additive manufacturing methods like 3D printing of turbine nozzles and rotors. These new possibilities provide potential to improve the competiveness of small-scale ORC. A simple air turbine design with plastic and metal components has been manufactured and tested.