@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} } @misc{FrankRoedderNeefetal.2018, author = {Frank, Lena and R{\"o}dder, Maximilian and Neef, Matthias and Adam, Mario}, title = {Heizung, L{\"u}ftung, Weiße Ware - Ein integriertes Systemkonzept f{\"u}r das Haus der Zukunft}, series = {KKA - K{\"a}lte Klima Aktuell}, volume = {37}, journal = {KKA - K{\"a}lte Klima Aktuell}, number = {4}, publisher = {Bauverl. BV}, issn = {0722-4605}, pages = {42 -- 47}, year = {2018}, language = {de} } @misc{FrankRoedderNeefetal.2020, author = {Frank, Lena and R{\"o}dder, Maximilian and Neef, Matthias and Adam, Mario}, title = {energiBUS4home - Integration von Haushaltsger{\"a}ten in ein multifunktionales W{\"a}rmepumpensystem}, series = {KI K{\"a}lte Luft Klimatechnik}, volume = {56}, journal = {KI K{\"a}lte Luft Klimatechnik}, number = {8/9}, publisher = {H{\"u}thig}, issn = {1865-5432}, pages = {41 -- 45}, year = {2020}, language = {de} } @inproceedings{RoedderFrankKirschneretal.2017, 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 = {12th Conference on Sustainable Development of Energy, Water and Environment Systems, 04.-08.10.2017, Dubrovnik}, booktitle = {12th Conference on Sustainable Development of Energy, Water and Environment Systems, 04.-08.10.2017, Dubrovnik}, editor = {The International Centre for Sustainable Development of Energy, Water and Environment Systems,}, year = {2017}, 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} } @inproceedings{RoedderNeefLauxetal.2015, author = {R{\"o}dder, Maximilian and Neef, Matthias and Laux, Christoph and Priebe, Klaus-P.}, title = {Systematic Fluid Selection for Organic Rankine Cycles (ORC) and Performance Analysis for a Combined High and Low Temperature Cycle}, series = {Volume 3: Coal, Biomass and Alternative Fuels; Cycle Innovations; Electric Power; Industrial and Cogeneration}, booktitle = {Volume 3: Coal, Biomass and Alternative Fuels; Cycle Innovations; Electric Power; Industrial and Cogeneration}, publisher = {American Society of Mechanical Engineers}, organization = {International Gas Turbine Institute}, isbn = {978-0-7918-5667-3}, doi = {10.1115/GT2015-42432}, year = {2015}, 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 and tolerance criteria. 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 and a low temperature cycle in which the condensation heat of the high temperature (HT) cycle provides the heat input of the low temperature (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 high temperature cycle with Toluene as the working fluid and 6,2\% in low temperature cycle with iso-Butane 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} } @inproceedings{HelmSpliethoffNeef2007, author = {Helm, Peter and Spliethoff, Hartmut and Neef, Matthias}, title = {Closing the Gap: Measuring Bristle Blow Down of Brush Seals}, series = {19 th International Conference on Fluid Sealing, Poitiers}, booktitle = {19 th International Conference on Fluid Sealing, Poitiers}, address = {Poitiers}, year = {2007}, language = {en} } @inproceedings{NeefHepermannSuerkenetal.2007, author = {Neef, Matthias and Hepermann, Florian and S{\"u}rken, Norbert and Schettel, Joachim}, title = {Brush Seal Porosity Modeling: Applicability and Limitations}, series = {ETC7 - 7th Conference on Turbomachinery, Athens}, booktitle = {ETC7 - 7th Conference on Turbomachinery, Athens}, address = {Athens}, year = {2007}, language = {en} } @inproceedings{NeefHummel2000, author = {Neef, Matthias and Hummel, Dietrich}, title = {Euler solutions for a finite-span flapping wing}, series = {"Fixed, flapping and rotary wing vehicles at very low Reynolds numbers, Notre Dame, Indiana, USA}, booktitle = {"Fixed, flapping and rotary wing vehicles at very low Reynolds numbers, Notre Dame, Indiana, USA}, year = {2000}, 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} } @inproceedings{NeefFusseneckerNiemannetal.2018, author = {Neef, Matthias and Fussenecker, Claudia and Niemann, J{\"o}rg and Zielke, Thomas}, title = {Publish your undergraduate research! A mandatory course for master students in engineering}, series = {Creativity, innovation and entrepreneurship for engineering education excellence : proceedings of the 46th SEFI Annual Conference 2018, Copenhagen, Denmark}, booktitle = {Creativity, innovation and entrepreneurship for engineering education excellence : proceedings of the 46th SEFI Annual Conference 2018, Copenhagen, Denmark}, editor = {Clark, Robin and Munkebo Hussmann, Peter and J{\"a}rvinen, Hannu-Matti}, publisher = {SEFI - Soci{\´e}t{\´e} Europ{\´e}enne pour la Formation des Ing{\´e}nieurs}, address = {Brussels}, organization = {European Society for Engineering Education SEFI}, isbn = {978-2-87352-016-8}, year = {2018}, abstract = {Undergraduate students in engineering often have little exposure to the world of scientific publishing and the culture of sharing research work. While the beneficial exchange between research and teaching is well promoted, while the benefits of conference participation for students have already been surveyed and while courses on scientific writing are readily available, the concept of mini-conferences as part of the curriculum combines all three aspects into one. Therefore, the course "Engineering Conferences" was developed and installed as a mandatory part of a master program for engineering students. The idea is to go beyond simply teaching the standards of academic writing and skills for using scientific publications. By using a learner-centered approach, the students are engaged in typical activities around an active attendance of a real conference. Based on their bachelor thesis, they write a paper complying with common academic standards, submit the paper and review submissions of their fellow students. They also produce a poster and defend their work in a poster session held publicly on campus. This contribution is based on the experience from the first four terms teaching the course. It explains the didactic rationale behind the concept and individual teaching modules, it comprises the collection of useful resources for teaching and organizing scientific publishing and it includes the consequences drawn from course evaluation results.}, language = {en} } @inproceedings{Neef2013, author = {Neef, Matthias}, title = {Innerst{\"a}dtische Nutzung von Kleinwindkraftanlagen: Potentiale und H{\"u}rden}, series = {M{\"u}lheimer Initiative f{\"u}r Klimaschutz, 06.05.2013}, booktitle = {M{\"u}lheimer Initiative f{\"u}r Klimaschutz, 06.05.2013}, address = {M{\"u}lheim an der Ruhr}, organization = {M{\"u}lheimer Initiative f{\"u}r Klimaschutz e.V.}, url = {http://nbn-resolving.de/urn:nbn:de:hbz:due62-opus-21017}, year = {2013}, language = {de} } @phdthesis{Neef2002, author = {Neef, Matthias}, title = {Analyse des Schlagfluges durch numerische Str{\"o}mungsberechnung}, volume = {ZLR-Forschungsbericht, 2}, url = {http://nbn-resolving.de/urn:nbn:de:gbv:084-14501}, pages = {245}, year = {2002}, abstract = {Mit Hilfe eines Finite-Volumen-Verfahrens wird die dreidimensionale reibungsbehaftete Stroemung um einen schlagenden Fluegel berechnet. Die Bewegungsparamter sind dabei vergleichbar mit den Bedingungen im Reiseflug grosser Voegel. Das numerische Verfahren wird fuer den gezeigten Anwendungsfall, indem eine Methode zur Realisierung von beliebigen periodischen Bewegungen implemetiert wird. Eine Verifizierung erfolgt durch den Vergleich mit analytischen, numerischen und experimentellen Ergebnissen aus der Literatur. Mit dem verifizierten Verfahren werden die instationaeren Groessen wie Druck und Geschwindigkeiten in der Umgebung des bewegten Fluegels berechnet. Daraus ergeben sich ferner die zeitlich gemittelten Groessen wie Schub und Wirkungsgrad des Schlagfluges. Ausserdem wird die Interaktion von Laengs- und Querwirbeln im Nachlauf des schlagenden Fluegels untersucht. Es zeigt sich ein dominanter Einfluss der pulsierenden Randwirbel aufgrund der endlichen Spannweite, waehrend die Anfahr- und Stoppwirbel, verursacht durch die Fluegelbewegung, im Reiseflug grosser Voegel nahezu vernachlaessigbar erscheinen.}, language = {de} } @inproceedings{HelmPugachevNeef2008, author = {Helm, Peter and Pugachev, Alexander and Neef, Matthias}, title = {Breaking the Swirl With Brush Seals: Numerical Modeling and Experimental Evidence}, series = {Proceedings of the ASME Turbo Expo 2008 : presented at the 2008 ASME Turbo Expo, June 9 - 13, 2008, Berlin, Germany}, volume = {4}, booktitle = {Proceedings of the ASME Turbo Expo 2008 : presented at the 2008 ASME Turbo Expo, June 9 - 13, 2008, Berlin, Germany}, publisher = {ASME}, address = {New York}, organization = {American Society of Mechanical Engineers Corporation; International Gas Turbine Institute Corporation}, isbn = {978-0-7918-4314-7}, doi = {10.1115/GT2008-50257}, pages = {1387 -- 1396}, year = {2008}, abstract = {Striving for smaller losses in turbomachinery has led to many advancements in the design of seals. Modern sealing concepts such as brush seals hold a great potential to increase the efficiency of both flight engines and stationary turbines. At the same time, in order to maintain stable operating conditions of the rotor, swirl-induced forces must be kept at a minimum in the sealing channels. Therefore, the influence of the permeable and flexible bristle pack of brush seals on the flow around the rotor surface must be known. In this paper the swirl flow in the cavities of two different seal geometries is studied experimentally and numerically. A conventional three-tooth labyrinth serves as a reference. A second seal arrangement with a bristle pack upstream of two teeth is compared with the reference labyrinth. The swirl is evaluated experimentally from total and static pressure measurements in various axial and circumferential positions. Additionally, the axial swirl distribution is calculated using computational fluid dynamics (CFD). Here, the numerical model of the brush seal is based on the porous medium approach and is calibrated using the experimental values of the leakage and the bristle clearance by adjusting the thickness of the bristle pack. The calibrated CFD model is then used to study the impact of the brush seal on the swirl component of the sealing flow. The observed significant decrease of the swirl by the brush seal shows good agreement with the experimental data. The impact of changes in bristle pack clearance on the swirl is also investigated and compared with experimental evidence. The aim is to show that the brush seals have a natural tendency to interrupt seal swirl. They can therefore be used for swirl control in order to create a beneficial impact on the dynamic stability of turbomachines.}, language = {en} } @inproceedings{NeefSuldaSuerkenetal.2006, author = {Neef, Matthias and Sulda, Erik and S{\"u}rken, Norbert and Walkenhorst, Jan}, title = {Design Features and Performance Details of Brush Seals for Turbine Applications}, series = {Proceedings of the ASME Turbo Expo 2006 : presented at the 2006 ASME Turbo Expo, May 6 - 11, 2006, Barcelona, Spain}, volume = {3}, booktitle = {Proceedings of the ASME Turbo Expo 2006 : presented at the 2006 ASME Turbo Expo, May 6 - 11, 2006, Barcelona, Spain}, publisher = {ASME}, address = {New York}, organization = {American Society of Mechanical Engineers Corporation; International Gas Turbine Institute Corporation}, isbn = {0-7918-4238-X}, doi = {10.1115/GT2006-90404}, pages = {1385 -- 1392}, year = {2006}, abstract = {Adaptive and contacting seals such as brush seals have been successfully applied to turbomachinery for several years. In large steam turbine applications, however, various challenges still persist. Special focus is directed at the long-term performance and longevity of brushes on conventional spring-backed seal segments in steam turbines. This issue is particularly related to wear during startup conditions. This paper discusses the results of wear tests, derived from simulated transient turbine behavior, where the resultant seal leakage under steady state conditions is monitored. It is shown that the brush seal is significantly capable of adapting to varying operating conditions, but exhibits a degree of performance degradation during the initial startups. Together with previously reported mid-term wear data and an experience based long-term phenomenological approach a general model for brush seal performance degradation is developed. This model can be used for performance prediction and exerts influence on brush seal design.}, language = {en} } @inproceedings{HurdTruckenmuellerThammetal.2005, author = {Hurd, Paul and Truckenmueller, Frank and Thamm, Norbert and Pollak, Helmut and Neef, Matthias and Deckers, Mathias}, title = {Modern Reaction HP/IP Turbine Technology Advances and Experiences}, series = {Proceedings of the ASME Power Conference - 2005 : includes papers from the 2005 International Conference on Power Engineering (ICOPE) ; presented at the 2005 ASME Power Conference, April 5 - 7, 2005, Chicago, Illinois, USA}, booktitle = {Proceedings of the ASME Power Conference - 2005 : includes papers from the 2005 International Conference on Power Engineering (ICOPE) ; presented at the 2005 ASME Power Conference, April 5 - 7, 2005, Chicago, Illinois, USA}, publisher = {ASME}, address = {New York}, isbn = {0-7918-4182-0}, doi = {10.1115/PWR2005-50085}, pages = {425 -- 435}, year = {2005}, language = {en} }