@article{DubberkeLinnemannAbbasetal.2018, author = {Dubberke, Frithjof H. and Linnemann, Matthias and Abbas, Wameedh Khider and Baumh{\"o}gger, Elmar and Priebe, Klaus-Peter and Roedder, Maximilian and Neef, Matthias and Vrabec, Jadran}, title = {Experimental setup of a cascaded two-stage organic Rankine cycle}, series = {Applied Thermal Engineering}, volume = {131}, journal = {Applied Thermal Engineering}, publisher = {Elsevier}, doi = {10.1016/j.applthermaleng.2017.11.137}, pages = {958 -- 964}, year = {2018}, abstract = {In combination with a bottoming cycle, operated with a pure fluid in transcritical mode, the usage of a zeotropic mixture as a working fluid appears to be exergetically favorable for power cycle efficiency in cascaded two-stage organic Rankine cycles (CORC). A CORC is set up and initially tested with cyclopentane and propane as working fluids in its high temperature and low temperature cycle, respectively. A thermal oil cycle serves as the heat source and is powered electrically with a maximum heat flow of 158 kW. The design of this experimental setup allows for a rapid replacement of individual components and for a wide range of conditions in terms of fluids and thermodynamic states. The components of all cycles and the measurement and control technology are described in detail. A testing procedure is presented, followed by a discussion of the measurement results, where it is shown that the intended concept of two cascaded organic Rankine cycles is operational and that the measured data are consistent.}, language = {en} } @article{FrankRoedderNeefetal.2021, author = {Frank, Lena and R{\"o}dder, Maximilian and Neef, Matthias and Adam, Mario}, title = {Heating, Ventilation, Domestic Appliances - an Energy Integrated System Concept for the Household of the Future}, series = {Energy}, volume = {234}, journal = {Energy}, publisher = {Elsevier}, issn = {0360-5442}, doi = {10.1016/j.energy.2021.121303}, year = {2021}, language = {en} } @article{BaierNeef2019, author = {Baier, Andr{\´e} and Neef, Matthias}, title = {Studierende lehren und lernen sozial-{\"o}kologische Verantwortung}, series = {Die Neue Hochschule}, volume = {60}, journal = {Die Neue Hochschule}, number = {5}, organization = {Hochschullehrerbund - Bundesvereinigung - e.V. (hlb)}, pages = {8 -- 11}, year = {2019}, language = {de} } @article{FesekerKinellNeef2018, author = {Feseker, Daniel and Kinell, Mats and Neef, Matthias}, title = {Experimental Study on Pressure Losses in Circular Orifices With Inlet Cross Flow}, series = {Journal of Turbomachinery}, volume = {140}, journal = {Journal of Turbomachinery}, number = {7}, address = {ASME}, doi = {10.1115/1.4039842}, pages = {210}, year = {2018}, abstract = {The ability to understand and predict the pressure losses of orifices is important in order to improve the air flow within the secondary air system. This experimental study investigates the behavior of the discharge coefficient for circular orifices with inlet cross flow which is a common flow case in gas turbines. Examples of this are at the inlet of a film cooling hole or the feeding of air to a blade through an orifice in a rotor disk. Measurements were conducted for a total number of 38 orifices, covering a wide range of length-to-diameter ratios, including short and long orifices with varying inlet geometries. Up to five different chamfer-to-diameter and radius-to-diameter ratios were tested per orifice length. Furthermore, the static pressure ratio across the orifice was varied between 1.05 and 1.6 for all examined orifices. The results of this comprehensive investigation demonstrate the beneficial influence of rounded inlet geometries and the ability to decrease pressure losses, which is especially true for higher cross flow ratios where the reduction of the pressure loss in comparison to sharp-edged holes can be as high as 54\%. With some exceptions, the chamfered orifices show a similar behavior as the rounded ones but with generally lower discharge coefficients. Nevertheless, a chamfered inlet yields lower pressure losses than a sharp-edged inlet. The obtained experimental data were used to develop two correlations for the discharge coefficient as a function of geometrical as well as flow properties.}, language = {en} } @article{BonkLauxRoedderetal.2017, author = {Bonk, Christian Dirk and Laux, Christoph and R{\"o}dder, Maximilian and Neef, Matthias}, title = {Design of a 1 KW Organic Rankine Cycle for Teaching and Research Issues}, series = {Energy Procedia}, volume = {129}, journal = {Energy Procedia}, publisher = {Elsevier}, doi = {10.1016/j.egypro.2017.09.117}, pages = {931 -- 938}, year = {2017}, abstract = {This paper deals with the design of a micro-scale ORC plant for teaching and research including the development of an automated control concept. The aim is to provide a safe and environmentally acceptable micro-scale heat engine, which can be developed, implemented and used in university labs for the education of students as well as for small research projects. The test rig allows the support of several learning outcomes on a multi-disciplinary level particularly for the implementation and simulation of small power systems. Special attention was given to the organic working fluid characteristics and its selection process. In addition to the above-mentioned performance goals, favourable safety properties and low global warming potential were decisive in the selection of the novel organic fluid called 3M™ Novec™ 649. The performance and the fluid behaviour of Novec 649 in a micro-scale power cycle are of major interest and the research goal for the test rig presented in this paper. Due to the expected power output of 1 kW, a scroll expander was chosen as the generator drive for the micro plant. In order to design the major parts of the ORC, the thermodynamic simulation software EBSILON®Professional was used. The supply temperature was set to 140 °C. As a result of the simulation, feasible expander inlet pressures spread from 5.5 bar to 8.5 bar. This leads to thermal efficiencies of the ORC in the order of 5 \%. Adding a recuperator to the cycle system decreases the operating pressure range but in the end, the thermal efficiency can be increased by 1.5 \%-points up to 6.2 \%. Finally, an automated control concept is introduced, where the pump is controlled via the fill level measurement system.}, language = {en} } @article{NeefZielkeFussenecker2017, author = {Neef, Matthias and Zielke, Thomas and Fussenecker, Claudia}, title = {„Engineering Conferences": Wissenschaftlich Kommunizieren im Master}, series = {Die Neue Hochschule}, volume = {58}, journal = {Die Neue Hochschule}, number = {3}, pages = {4}, year = {2017}, language = {de} } @article{RoedderNeefLauxetal.2016, author = {Roedder, Maximilian and Neef, Matthias and Laux, Christoph and Priebe, Klaus-P.}, title = {Systematic Fluid Selection for Organic Rankine Cycles and Performance Analysis for a Combined High and Low Temperature Cycle}, series = {Journal of Engineering for Gas Turbines and Power}, volume = {138}, journal = {Journal of Engineering for Gas Turbines and Power}, number = {031701}, publisher = {ASME}, doi = {10.1115/1.4031361}, pages = {168}, year = {2016}, abstract = {The organic Rankine cycle (ORC) is an established thermodynamic process that converts waste heat to electric energy. Due to the wide range of organic working fluids available the fluid selection adds an additional degree-of-freedom to the early design phase of an ORC process. Despite thermodynamic aspects such as the temperature level of the heat source, other technical, economic, and safety aspects have to be considered. For the fluid selection process in this paper, 22 criteria were identified in six main categories while distinguishing between elimination (EC) and tolerance criteria (TC). For an ORC design, the suggested method follows a practical engineering approach and can be used as a structured way to limit the number of interesting working fluids before starting a detailed performance analysis of the most promising candidates. For the first time, the selection process is applied to a two-stage reference cycle, which uses the waste heat of a large reciprocating engine for cogeneration power plants. It consists of a high temperature (HT) and a low temperature (LT) cycle in which the condensation heat of the HT cycle provides the heat input of the LT cycle. After the fluid selection process, the detailed thermodynamic cycle design is carried out with a thermodynamic design tool that also includes a database for organic working fluids. The investigated ORC cycle shows a net thermal efficiency of about 17.4\% in the HT cycle with toluene as the working fluid and 6.2\% in LT cycle with isobutane as the working fluid. The electric efficiency of the cogeneration plant increases from 40.4\% to 46.97\% with the both stages of the two-stage ORC in operation.}, language = {en} } @article{WolterZekornNeef2016, author = {Wolter, Nina and Zekorn, Thomas and Neef, Matthias}, title = {Station{\"a}re thermodynamische Prozesssimulationen am Beispiel eines Industriekraftwerks}, series = {BWK: das Energie-Fachmagazin}, volume = {68}, journal = {BWK: das Energie-Fachmagazin}, number = {6}, pages = {6 -- 10}, year = {2016}, abstract = {Um bauliche Ver{\"a}nderungen in bestehenden Kraftwerksprozessen auf ihre Wirkungsweise untersuchen und thermodynamisch beziehungsweise wirtschaftlich bewerten zu k{\"o}nnen, werden thermische Kraftwerksprozesse mit geeigneter Simulationssoftware abgebildet und in verschiedenen Detaillierungsstufen ausgelegt oder nachgerechnet. Im Folgenden wird ein Weg aufgezeigt, wie mit Hilfe einer station{\"a}ren Simulationssoftware die Gesamtjahresbilanz eines Kraftwerks vorausberechnet werden kann. Mit Hilfe von Prozessdaten aus Vorjahren wird nachgewiesen, dass das Berechnungsmodell das bestehende Kraftwerk mit einer Abweichung von weniger als drei Prozent bez{\"u}glich erzeugter elektrischer Leistung und Brennstoffeinsatz und bei bekannter Dampfproduktion abbilden kann. Das so verifizierte Modell kann zur Untersuchung von Zubaumaßnahmen oder Ver{\"a}nderungen im Kraftwerksprozess eingesetzt werden.}, language = {de} } @article{NeefFritzenSchumacher2003, author = {Neef, Matthias and Fritzen, J. P. and Schumacher, G.}, title = {Evaluation of mount loads in dynamic testing of a jet engine}, series = {Mechanical Systems and Signal Processing}, volume = {17}, journal = {Mechanical Systems and Signal Processing}, number = {3}, publisher = {Elsevier}, doi = {10.1006/mssp.2001.1405}, pages = {665 -- 681}, year = {2003}, abstract = {In the dynamic testing of jet engines the evaluation of loads on the mount structure is vital for comparison with finite element calculations of such testing. Measuring these loads with the help of strain gauges applied to the structure becomes difficult if the mount is overdetermined and thus not every strain gauge can be assigned to a single load direction. In this study, the overdetermined mount structure of the BR715 engine was examined at one of the three mounting points between the Boeing 717 airframe and the engine, where loads in five directions were reacted. Firstly, the dependence of five measured strains upon known static load conditions at the mounting point had to be determined. For this purpose a static calibration test was carried out where defined forces and moments in known directions were applied to the structure while the output from five strain gauges was measured accordingly. The result was the desired relationship between loads and strains in terms of a matrix, which yields the corresponding load condition of the examined mounting point if multiplied with a set of strains. The same calibration procedure was carried out with a finite element model of the mount, where direct comparison to dynamic load results from the model itself was possible. With this model the validity of the above method was shown as well as possible errors which may occur while evaluating dynamic test results. The method was found to give satisfactory results even for dynamic loading, although some inertia forces disturb the signals in dynamic testing. Finally, the results from an actual dynamic engine test were processed into loads and then compared to the simulated loads from a finite element model of the engine. Good agreement was found and the indication of any remaining discrepancies was used to update the model for an even better representation of the dynamic test loads.}, language = {en} } @article{RoedderFrankKirschneretal.2018, author = {R{\"o}dder, Maximilian and Frank, Lena and Kirschner, Daniel and Neef, Matthias and Adam, Mario}, title = {EnergiBUS4home - Sustainable energy resourcing in low-energy buildings}, series = {Energy}, volume = {159}, journal = {Energy}, publisher = {Elsevier}, doi = {10.1016/j.energy.2018.06.145}, pages = {638 -- 647}, year = {2018}, language = {en} }