Temperature inhomogeneities and their influence on proton exchange membrane (PEM) water electrolyzer performance of industrial-scale stacks were investigated. Three temperature differences were examined: between the inlet and outlet, in-between the cells of a stack, and between the cell’s solid materials and the fluids. A validated stack model for temperature and performance is presented which is used to quantify the above-mentioned temperature fields and their influence on current density distribution and cell voltages. For a chosen scenario, with current densities of 2.0 A cm-2, fluid inlet temperatures of 60°C and flow-rates of 0.15 kg s-1m-2, peak temperature differences amount to 8.2 K along-the-channel. This relates to inhomogeneities of current density of up to 10% inside a cell and deviations of cell voltage of 9 mV in-between cells in the center of the stack and outer cells. For higher current densities these differences increased further. More homogeneous temperatures allow operation at elevated average temperatures without exceeding temperature limitations and reduce the spread of degradation mechanisms. Hence, homogenous profiles lead to a more hole-some utilization of electrolysis stacks. Therefore, the ability to homogenize via alternative operation such as higher flow-rate, higher pressure and altered routing of fluid-flow is analyzed.

Steady flow in axial one-stage turbines is assessed numerically and experimentally. The simulations are performed on coarse meshes using a standard numerical approach (3D, steady state, kε-turbulence model, wall function at solid boundaries). In order to allow for conclusions drawn from these rapid numerical studies, the approach was compared with an explicit LDA (Laser Doppler anemometry) mapping of the velocity field downstream the rotor on a representative turbine stage. A two-component LDA system allowed for measurements of axial and tangential velocity components at varying depth (radius) in the flow channel, Measurements thus correspond to a full plane at constant axial position in the rotating frame of reference of the rotor. Comparison between LDA velocity mapping and CFD results shows good agreement. A series of subsequent simulations is thus used to judge the impact of varied blade/stage design parameters. Two turbine layouts are defined for identical operating conditions and shaft power. The flow in the unshrouded rotor blade row is analyzed for the influence of varying tip clearance size and the dependency on stage velocity triangles. – Known correlations for tip clearance losses (typically used in mean line predictions) are used, though the blade row geometry considered is beyond the limits the correlations are intended for. The absolute loss level found in CFD simulations differs significantly from what is expected when using loss correlations. Still the variation with tip gap size is predicted well by some of the investigated models. As dependency of tip clearance losses on stage velocity triangles is considered, none of the tested correlations gives results consistent with the numerical simulations. The use of standard correlations ‘beyond the limits’ is thus considered to introduce high uncertainty. Due to the good consistency between LDA and numerical results, the conclusions are considered to be valid for stage designs similar to the ones analyzed.

An upgrade of the lean premixed combustion system installed in the SGT5-8000H in Irsching/Germany was developed for the 50 Hz and 60 Hz versions of the SGTX-8000H gas turbines. It features lower CO and NOx emissions by improving combustion aerodynamics and reduction of the air consumption of the combustion system. Furthermore an improved secondary air managing system increases the amount of air, which can be supplied in a controllable way to the turbine in part load operation and, thus, increases the combustor temperature. This is done in stepwise increasing the air mass flow to the turbine by feeding compressor exit air to different distinct turbine stages. All in all this system extends the turn down capability beyond the level achievable by the new combustion system alone. The new combustion system and the secondary air managing system were installed in full scale and tested in the SGT6-8000H test facility of the Siemens Gas turbine plant in Berlin. The results have subsequently successfully been validated in the first commercial application on a customer site. This paper presents the technical features of the systems, the development program and the test results.

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