@misc{BergKleisslHimmelbergetal., author = {Berg, Heinz Peter and Kleissl, Marko and Himmelberg, Axel and Lehmann, Mario and Prechavut, Nontavut and Vorpahl, Michael}, title = {Heat balancing of direct reforming fuel cells in MGT-SOFC hybrid systems}, series = {9th Thai Society of Mechanical Engineers, International Conference on Mechanical Engineering (TSME-ICoME 2018) 11-14 December 2018, Phuket, Thailand}, journal = {9th Thai Society of Mechanical Engineers, International Conference on Mechanical Engineering (TSME-ICoME 2018) 11-14 December 2018, Phuket, Thailand}, editor = {Prukvilailert, Monchai}, edition = {1. Auflage}, publisher = {IOP Publishing/IOP Science}, address = {Bristol}, issn = {1757-899X}, doi = {10.1088/1757-899X/501/1/012007}, pages = {50 -- 60}, abstract = {Solid oxide fuel cells convert chemical energy in electrical energy and are highly suitable for the conversion of hydrocarbon based fuels and products from PowerToGas conversions. Embedded in a micro gas turbine-cycle instead of the combustion chamber the heat energy of the injected fuel, released in the SOFC-Stack, can additionally converted into work and by a turbine-generator into electricity. In a compact system, SOFC stacks are designed to realize a direct steam-reforming process inside. In such direct-reforming fuel cell systems the SOFC operating temperature due to the heat demand for reforming, can be reduced to a value in the range of the outlet temperature of the downstream flow (650°C). If the cycle uses a recuperating system, the operating conditions of the SOFC can be realized without additional high-temperature heat exchanger systems. The system with an uncooled turbine, described in [1], just can reach the operating temperature with an additional high-temperature heat exchange. The system described in this publication does not require an additional high-temperature heat exchanger, because the X-value, as the ratio between the exchanged heat quantity and the required amount of heat to complete the MGT-cycle [2] due to the referring process, is nearly zero and can be realized via the inner container wall (of the MLC). The cycle is completed (between the SOFC and the turbine entry) by the heat input of an afterburner. Here the unreacted fuel of the SOFC fuel-stream is used to provide the necessary heat energy for the downstream turbo-generator-system.}, language = {en} } @inproceedings{BergDueckershoffLehmannetal., author = {Berg, Heinz Peter and D{\"u}ckershoff, Roland and Lehmann, Mario and Prechavut, Nontavut}, title = {Micro Turbo-Fuel-Cell-Technology : Hybrid compact turbo machinery technology and thermodynamic aspects regarding design parameters of a high efficient MGT-SOFC-system}, series = {12th European Conference on Turbomachinery Fluid dynamics \& Thermodynamics}, booktitle = {12th European Conference on Turbomachinery Fluid dynamics \& Thermodynamics}, doi = {10.29008/ETC2017-266}, pages = {1 -- 12}, abstract = {The improvement of decentralised energy supply systems has received an important role in the recent years. One option is the combination of SOFC with recuperated MGT. Here, a new strategy for selecting the system parameters, such as the operating temperature of the SOFC, turbine inlet temperature and the pressure ratio of the hybrid system, is presented. By introducing the heat ratio between the heat required to increase the process gas to the SOFC operating temperature and the heat required to raise the SOCF exhaust gas to the TIT, it was found that high efficiency (approx. 68\%) is realisable in a compact hybrid system today. Analysis also shows that the HEX-technology is needed to improve the system effectiveness. Also, high recirculation rates with lower TIT can be considered as the future development direction. In addition, a sample configuration of an oil-free MGT rotor unit with high speed foil bearings is presented.}, language = {en} } @inproceedings{BergDueckershoffLehmannetal., author = {Berg, Peter and D{\"u}ckershoff, Roland and Lehmann, Mario and Prechavut, Nontavut}, title = {Micro Turbo-Fuel-Cell-Technology: Hybrid compact turbo machinery technology and thermodynamic aspects regarding design parameters of a high efficient MGT-SOFC-system}, series = {Proceedings of 12th European Conference on Turbomachinery Fluid dynamics \& Thermodynamics, ETC12, April 3 - 7, 2017, Stockholm, Sweden}, booktitle = {Proceedings of 12th European Conference on Turbomachinery Fluid dynamics \& Thermodynamics, ETC12, April 3 - 7, 2017, Stockholm, Sweden}, abstract = {The improvement of decentralised energy supply systems has received an important role in the recent years. One option therefore is the combination of SOFC with a recuperated MGT. Here, a new strategy for selecting the system parameters, such as the operating temperature of the SOFC, the turbine inlet temperature and the pressure ratio of the hybrid system, is presented. By introducing the heat ratio between the heat required to increase the process gas to the SOFC operating temperature and the heat required to raise the SOCF exhaust gas to the TIT, it was found that high efficiency (approx. 68\%) is realisable in a compact hybrid system today. Analysis also shows that the HEX-technology is needed to improve the system effectiveness. Also, high recirculation rates with lower TIT can be considered as the future development direction. In addition, a sample configuration of an oil-free MGT rotor unit with high speed foil bearings is presented.}, language = {en} } @inproceedings{PrechavutBerg, author = {Prechavut, Nontavut and Berg, Heinz Peter}, title = {An Experimental Study on Structural Characteristics of Cantilever-Type Foil Bearings}, series = {Deutscher Luft- und Raumfahrtkongress 2015}, booktitle = {Deutscher Luft- und Raumfahrtkongress 2015}, publisher = {Deutsche Gesellschaft f{\"u}r Luft- und Raumfahrt - Lilienthal-Oberth e.V.}, address = {Bonn}, url = {http://nbn-resolving.de/urn:nbn:de:101:1-201511275091}, abstract = {Capable of high-speed and high-temperature operation, together with an "oil-free" technology concept, gas foil bearings are a perfect solution for a novel light weight (small scale) turbo machinery. While the gas film geometry and the pressure build-up are similar to other gas lubricated bearings, and as it has been well formulated in the hydrodynamic lubrication theory, the compliant structure of the foil bearings have a variety of forms and characteristics. The cantilever-type of foil bearings are one sort of foil bearings that uses a pattern of small cantilever beams as support structure which is very robust and eases the manufacturing process. The aim of this paper is to present a measurement method and results of structural stiffness and damping characteristics of exemplary 50 mm tree-lobes radial foil bearings. Static structural test result shows that the bearing has a wide range of linear stiffness in the bearing's center area. The ramp of cartridge inner surface contour causes a cross coupling effect which may cause instability by a large rotor orbit. Increasing in bear - ing preload result in slightly increasing in static stiffness. In dynamic excitation test, the result shows that the dynamic stiffness is about three times higher than the static one. With a simple model of dry friction, the result shows that the dry friction coefficient is in a range of 0.4 to 0.7. The result also shows that the dynamic stiffness is more sensitive to vibration amplitude than frequency. While the damping decreases significantly with exciting frequency, especially at the vicinity of the rigid body resonance. The result evidence that the magnitude of displacement has a great effect on damping. As displacement amplitude decreases, the bearing is better in damping.}, language = {en} }