@misc{XieMathiazhaganBarkowskietal., author = {Xie, Tianxiao and Mathiazhagan, Akilan and Barkowski, Daniel and Starick, Tommy and Berg, Heinz Peter and H{\"o}schler, Klaus}, title = {Comparison of convective heat transfer in metal foam-filled channels of three different cross-sections}, series = {Numerical Heat Transfer, Part A: Applications}, volume = {85}, journal = {Numerical Heat Transfer, Part A: Applications}, number = {2}, issn = {1521-0634}, doi = {10.1080/10407782.2023.2181892}, pages = {222 -- 236}, abstract = {This work introduces a new approach of analyzing convective heat transfer in porous medium by considering the foam structure as a type of fin. It provides the resulting heat transfer characteristics for the design of a longitudinally flowed tube bundle reformer used for the Micro Gas Turbine Solid Oxide Fuel Cell (MGT-SOFC) hybrid process. Owing to a limited experimental database available in literature for the above-mentioned situation, a physical model is initially introduced for a channel flow configuration between two large flat plates using a commercial PDE solver. This model is then validated with experimental results available in literature. A comparison with theoretical solutions is also conducted. Later, this model is modified/adapted for a pipe flow configuration. The physical model for a channel with representative cross-section shape of a longitudinally flowed tube bundle is more complex and is therefore built in a commercial CFD-Solver. A comparative study of the heat transfer behavior in channels of different cross-sections is performed based on a new dimensionless correlation, whose physical coherence with fin efficiency is explained and mathematically proved. The applicability of the heat transfer correlation from one cross-sectional shape to the other are discussed. The proposed new treatment of the porous medium as a fin structure considerably simplifies the heat transfer analysis in porous medium by the clear physical meaning behind fin efficiency and Biot number. This relationship contributes to a better understanding of the heat heat transfer characteristics in porous media in contrast to the correlation between Nusselt number and Reynolds number. Furthermore, this correlation enables a direct comparison between foam structures of different parameters because the fin efficiency is always between 0 and 1. The strong physical background of new correlations also enhances the reliability and plausibility at characterizing and designing the metal foam for heat transfer enhancement.}, language = {en} } @misc{DueckershoffBergKleissletal., author = {D{\"u}ckershoff, Roland and Berg, Heinz Peter and Kleissl, Marko and Walther, Aniko and Himmelberg, Axel}, title = {Flexibilization of an MGT-SOFC hybrid system for electricity and hydrogen production for the realization of a sustainable hydrogen economy}, series = {AIP Conference Proceedings}, volume = {3086 (2024)}, journal = {AIP Conference Proceedings}, number = {1}, doi = {10.1063/5.0205000}, abstract = {The turbo fuel cell is a hybrid combination of a micro-gas turbine (MGT) and solid oxide fuel cells (SOFC). It will contribute to an environmentally friendly, reliable and affordable energy supply due to its high electrical efficiency and low line losses in close proximity to residential districts. The turbo fuel cell (MGT-SOFC hybrid system) makes it possible to increase independence from fossil fuels by choosing a fuel cell type with maximum fuel flexibility embedded in a turbo machine process. This hybrid technology makes it possible to transform the existing fossil gas economy into a hydrogen economy. This technology converts products from "power-to-X-gas" conversions from renewable energies into electrical energy with the highest conversion efficiency and thus contributes to the goal of stopping CO2 emissions by 2050. The turbo fuel cell supplies energy exactly where it is needed. The principle-related waste heat can be used for building air conditioning (heating or cooling) systems. Thanks to the condensing technology, an overall efficiency of over 96\% can thus be demonstrated. Additionally, it contributes to grid stability through high flexibility and cluster capability. For methane to be converted into electricity in a turbo fuel cell, a synthesis gas is generated from a CH4 partial flow via an integrated pre-reformer according to the principle of steam reforming. Through high-temperature separation after the pre- reformer, hydrogen can be extracted from the synthesis gas and discharged for use in other applications (e.g., hydrogen mobility). Hydrogen extraction does not lead to a deterioration of electrical efficiency, which is about 70\% in the system under consideration. In the living spaces of tomorrow, hydrogen and electrical energy for mobility can thus be provided even before the realisation of a supra-regional hydrogen supply economy. Decarbonisation of the energy economy can be advanced through the introduction of this technology. In this publication, it is shown how important this technology is for the introduction of a hydrogen economy with the inclusion of existing infrastructure.}, language = {en} } @misc{PoojitganontAntoshkivSinchaietal., author = {Poojitganont, Thanapol and Antoshkiv, Oleksiv and Sinchai, Jirathiwat and Watjatrakul, Boonchai and Berg, Heinz Peter}, title = {Numerical investigation of catalytic afterburner at various operational conditions}, series = {AIP Conference Proceedings}, volume = {3086}, journal = {AIP Conference Proceedings}, number = {1}, publisher = {AIP Publishing}, doi = {10.1063/5.0214515}, pages = {1 -- 10}, abstract = {The system of hydrogen catalytic oxidation is applied in various industrial applications; for example, afterburning of fuel cell exhaust gases, removing of hydrogen residues from electrolysis gas, catalytic drying processes. Since the reaction rate is directly proportional to the surface area of the coating material, a number of small lattice slots is augmented. However, the slots also cause the increment of pressure losses on the system. In this study, CFD simulation is applied to investigate the physical and chemical phenomena in catalytic burners. Multiple slotted afterburners are modeled with slot densities of 1xC to 4xC cells per square inch (cpsi). The air mass flow rates vary from 20 to 100 g/s. The outlet velocities are validated using the experimental data. In parallel, the alternative simulation method using the porous media model is also employed. In order to simulate both homogeneous and heterogeneous oxidation, the chemical kinetics of hydrogen and carbon dioxide in Chemkin format are implemented. The calculated results are compared with the correlated experimental data. Furthermore, the variations of inlet pressure and temperature are also discussed.}, language = {en} } @misc{BergBarkowskiButt, author = {Berg, Heinz Peter and Barkowski, Daniel and Butt, Usman}, title = {Determination of local internal heat transfer in the cooling channels of turbine blades with a validated calculation method considering special boundary layer phenomena}, series = {AIP Conference Proceedings}, volume = {3086}, journal = {AIP Conference Proceedings}, number = {1}, doi = {10.1063/5.0206142}, abstract = {In the present publication, a validation by means of the dimensionless ratios between the calculation of heat transfer coefficients and the experiment on an isothermally rotating device is performed. The investigations provide important insights into the design of internal cooling channels of turbine blades. It is shown that forced convection is dominant. For this reason, an isothermally rotating tube is chosen for the validation. This leads to further precision of the validation, since the buoyancy effect (described by the Archimedes-Number of rotations, Ar ≈ 0) in the axial direction is eliminated. The variation to determine the dimensionless heat transfer Nu-Number takes place in the ratio range Reynolds (Re)-Numbers = 8,500 to 52,000, Rotational (Ro)-Numbers = 0 to 0,2 and at a Prandtl (Pr)-Number of 2.5. In order to keep the isothermal conditions and to get an extremely high local resolution of the Nu-Numbers, experimental investigations were carried out with the Heat- and Mass- Transfer-Analogy. This is possible because the differential equations (energy / concentration) are the same at small Mach-Numbers (Ma ≈0) and the Stefan-current is negligible. By analogy with the Nu-Number, a dimensionless mass transfer Sh-Number could be chosen. The dimensionless Pr- Number then corresponds to the dimensionless Schmidt (Sc) -Number. Local Sh-Numbers (and thus the Nu-Numbers) could be determined with high resolution via the layer thickness loss of the sublimate (naphthalene /air system, Sc =2.5). The local Sh-Number and thus the Nu-Number are known. The Nu, Sh results are determined as a function of the Re- and Ro-Number (related to the pipe diameter), in the pipe circumferential direction φ and dimensionless length x/d (with and without hydraulic flow) for the Pr, Sc-number and compared with the numerical calculations and the correlation. It could be shown that the use of a sublimate results in the following advantages for the validation: no vagrant heat flows in the wall, exact compliance with the boundary condition, pipe wall temperature = const (since wall concentration is constant) and Ar ≈ 0. Thus, for the numerical investigation (with Pr, Sc = 2.5), the boundary conditions could be accurately reproduced and compared with the experimental results and correlation. The numerical flow problem was solved using the steady-state Reynolds-averaged Navier-Stokes (RANS) equations. For the closure problem, the Boussinesq approximation was used. The turbulent eddy viscosity of the Boussinesq approximation was calculated using turbulence models (Menter-SST model and the SST transition model). The SST- turbulence model was shown to be a very good fit. The experimental results including the laminar turbulent transition could be reproduced very well with a high precision. A high technical importance for the design of turbine cooling systems could be shown.}, language = {en} } @misc{BergHimmelbergDueckershoffetal., author = {Berg, Heinz Peter and Himmelberg, Axel and D{\"u}ckershoff, Roland and Kleissl, Marko and Ring, Uwe}, title = {Simulations using dimensionless key figures for the design and optimization of compact, hybrid MGT-SOFC systems of the "Turbo Fuel Cell" type for high efficiency}, series = {14th European Conference on Turbomachinery Fluid dynamics \& Thermodynamics : ECT14, April 12-16 2021; Gdansk, Poland}, journal = {14th European Conference on Turbomachinery Fluid dynamics \& Thermodynamics : ECT14, April 12-16 2021; Gdansk, Poland}, doi = {10.29008/ETC2021-644}, abstract = {The "Turbo Fuel Cell" represents a highly integrated and highly compact technology system of a micro gas turbine fuel cell cycle (MGT-SOFC). It provides the solution for a highly efficient reverse electricity generation with an electrical efficiency of at least 68\% (status 2020-21) to approx. 75-80\% (in the future). In the context of industrial research on such a hybrid process, adapted, dimensionless parameters should be used in the design and optimization of the overall system. As an example, simulations of thermally optimized solutions to improve the energy yield using various dimensionless key figures are presented. Above all, heat integration measures enable an increase in system efficiency and a reduction in primary energy input. On the basis of exergetic analyzes by use of a modified Heat Balance Factor Y, as presented at ETC12, and the consideration of the SOFC enthalpy spread j, as well as a highly integrative use of the High Temperature Heat Exchanger Function F, it is shown how the hybrid cycle process efficiency can be optimized through innovative coupling of the individual heat flows. Measures to change the hybrid process can be used to deliberately shift the useful energy from the predominant heat yield in order to optimize electrical efficiency. A developed system enables primary energy to be used with the highest possible efficiency. The primary fuel used here is gaseous primary energy in the form of methane (natural gas) and hydrogen from renewable sources. Treatment mechanisms, such as the reforming of the methane used, and the targeted use of modern heat insulation and recovery mechanisms also have been considered. For the optimized hybrid system, total electrical efficiencies of more than 68\% could be demonstrated and additional thermal energy for heating purposes could be extracted. Ultimately, overall efficiencies for the utilization of the energy content of the primary energy of up to 97\% can be achieved. Energy converters with a maximum system output of around 200-300kW were examined. In the near future, such plants can replace existing fossil power plants being part of decentralized network systems. By their flexibility, they can guarantee the necessary security of power supply.}, language = {en} } @misc{BergDueckershoffVorpahletal., author = {Berg, Heinz Peter and D{\"u}ckershoff, Roland and Vorpahl, M. and Himmelberg, Axel}, title = {Results of the measurement of SOFC fuel cell stacks under pressure conditions}, series = {IOP Conference Series: Materials Science and Engineering}, volume = {1137}, journal = {IOP Conference Series: Materials Science and Engineering}, doi = {10.1088/1757-899X/1137/1/012009}, pages = {1 -- 11}, abstract = {Results from the measurement of SOFC fuel cell stacks under pressure conditions are presented. As part of a measurement campaign, the operation of a stack system is investigated, particularly under the operating conditions of a recuperated micro gas turbine. Above all, the performance and effectiveness of selected stack types at various operating pressures and operating temperatures are measured. With the test facility set up for such investigations, cell systems could be examined under atmospheric conditions and with pressures of up to 5 bar. It is shown that in operating conditions under pressure, the output of the fuel cell systems are improving. From a gauge pressure of 4 bar, the performance curve is flattened and higher pressures only produced a marginal increase in performance. Furthermore, the cells tested at overpressure show a steady-state behavior more quickly under load change requirements than in atmospheric operation. This means that more flexible operating modes with faster response behavior can be realized. By choosing a suitable operating temperature, the efficiency of the system is further increasing. Care was taken to select the operating conditions of the cell systems so that coking can be prevented. Finally, a statement can be made about the pressure dependence of the fuel conversion rate. Parasitic reactions at the anode can be related to the power output. The tests carried out have shown that the high-temperature fuel cell is a promising service provider of the future. A combination of SOFC high-temperature fuel cells and micro gas turbines in one machine could, in addition to the internal provision of the required pressure, also lead to better dynamics of the entire system and increase the energy yield from the primary energy source.}, language = {en} }