Robert Stieglitz

Validation of NEPTUNE-CFD Two-Phase Flow Models Using Experimental Data

This paper deals with the validation of the two-phase flow models of the CFD code NEPTUNEC-CFD using experimental data provided by the OECD BWR BFBT and PSBT Benchmark. Since the two-phase models of CFD codes are extensively being improved, the validation is a key step for the acceptability of such codes. The validation work is performed in the frame of the European NURISP Project and it was focused on the steady state and transient void fraction tests. The influence of different NEPTUNE-CFD model parameters on the void fraction prediction is investigated and discussed in detail. Due to the coupling of heat conduction solver SYRTHES with NEPTUNE-CFD, the description of the coupled fluid dynamics and heat transfer between the fuel rod and the fluid is improved significantly. The averaged void fraction predicted by NEPTUNE-CFD for selected PSBT and BFBT tests is in good agreement with the experimental data. Finally, areas for future improvements of the NEPTUNE-CFD code were identified, too.

Blankets – key element of a fusion reactor – functions, design and present state of development

Abstract Blankets are key elements of a future fusion power reactor, as they breed the fusion fuel tritium, extract the heat from the reactor for power generation and contribute to the nuclear shielding of the plasma confining magnetic field coils. On the way to the engineering implementation of fusion, in particular the blanket design approach has changed substantially. Novel blanket designs require, already from the beginning, incorporating close coupling of plasma physics with engineering physics to develop robust solutions coping with thermal, mechanical and also electrodynamic loads – not only during the stationary operating phase, but also during transients. Simultaneously, nuclear licensing feasibility as well as component failure safety must be part of the design approach. This article describes advanced blanket design approaches undertaken in the past years by the example of the helium cooled pebble bed blanket (HCPB), aiming at an efficient blanket engineering design, starting from the development of modular integral reactor analysis tools, via design analysis and engineering validation of fabrication and interface performance, towards safety analysis on the reactor level.

Development of high temperature liquid metal test facilities for qualification of materials and investigations of thermoelectrical modules

Three classes of experimental liquid metal facilities have been completed during the LIMTECH project aiming the qualification of materials, investigation of thermoelectrical modules, investigation of sodium transitional regimes and fundamental thermo-dynamical flows in concentrating solar power (CSP) relevant geometries. ATEFA facility is dedicated to basic science investigation focussed on the alkali metal thermal-to-electric converter (AMTEC) technology. Three SOLTEC facilities are aimed to be used in different laboratories for long term material investigation sodium environment up to a 1000 K temperature and for long term tests of AMTEC modules. The medium scale integral facility KASOLA is planned as the backbone for CSP development and demonstration.

Design and construction of the ATEFA facility for experimental investigations of AMTEC test modules

The Alkali Metal Thermal-to-Electric Converter (AMTEC) is an electrochemical cell that requires a high temperature heat source to generate electricity. At KIT the AMTEC technology is being investigated focusing on the use of concentrating solar energy as heat source. First a review on AMTEC technology is given. Further, the design and realization phases of the AMTEC Test Facility (ATEFA) and AMTEC test cell are presented, including the data acquisition and control system and two key technology developments: a ceramic to metal joint for high temperatures (800 – 1000 °C) and the magnetron sputtering of cathode layers on the ceramic electrolyte. The sheet resistance of several electrode samples has been analyzed using the 4-point probe technique and the microstructure of the cathode layer has been examined using the scanning electron microscopy (SEM).

A New Coupled CFD/Neutron Kinetics System for High Fidelity Simulations of LWR Core Phenomena: Proof of Concept

The Institute for Neutron Physics and Reactor Technology (INR) at the Karlsruhe Institute of Technology (KIT) is investigating the application of the meso- and microscale analysis for the prediction of local safety parameters for light water reactors (LWR). By applying codes like CFD (computational fluid dynamics) and SP3 (simplified transport) reactor dynamics it is possible to describe the underlying phenomena in a more accurate manner than by the nodal/coarse 1D thermal hydraulic coupled codes. By coupling the transport (SP3) based neutron kinetics (NK) code DYN3D with NEPTUNE-CFD, within a parallel MPI-environment, the NHESDYN platform is created. The newly developed system will allow high fidelity simulations of LWR fuel assemblies and cores. In NHESDYN, a heat conduction solver, SYRTHES, is coupled to NEPTUNE-CFD. The driver module of NHESDYN controls the sequence of execution of the solvers as well as the communication between the solvers based on MPI. In this paper, the main features of NHESDYN are discussed and the proof of the concept is done by solving a single pin problem. The prediction capability of NHESDYN is demonstrated by a code-to-code comparison with the DYNSUB code. Finally, the future developments and validation efforts are highlighted.

Einfluss der Konzentration auf solarthermische Systeme

Die solare Einstrahlung gleicht der eines schwarzen Strahlers mit 5576 K und besitzt eine hohe Exergie. Die Leistungsdichte dagegen entspricht einem Strahler mit 121 °C. Fur viele Anwendungen ist dies zu wenig, um eine ausreichende Betriebstemperatur (oder Exergie) sowie eine wirtschaftliche Flachennutzung zu erreichen. Mittels konzentrierender Spiegel wird die Leistungsdichte am Empfanger erhoht. Das Konzentrationsverhaltnis aus Spiegel- und Empfangerflache ist jedoch begrenzt. Die theoretische Begrenzung wird im Folgenden mittels des 2. Hauptsatzes der Thermodynamik abgeleitet. Wichtiger sind jedoch Einschrankungen durch die technischen oder physikalischen Eigenschaften der Spiegel oder Konzentratoren und den Empfanger oder Absorber. Den Zusammenhang von deren Qualitat und Anwendungsfallen werden aufgezeigt.

Impuls- und Energietransport in solarthermischen Systemen

Die Abschn. 3.3–3.5 behandelten bereits die Berechnung des Kollektorwirkungsgrades und der darin auftretenden Verluste. Dort wurde auf die detaillierte Diskussion der einzelnen passiven wie insbesondere auch aktiven Verlustmechanismen verzichtet. Die Erarbeitung der passiven Mechanismen zur Aufnahme solarer Einstrahlung im vierten Kapitel erlaubt nun einen neuen und fundierteren Einblick in die Beurteilung der konstruktiven Gestaltung sowie der anlagenbaulichen Realisation solarthermischer Systeme. Die darin gewonnen Erkenntnisse zeigen, dass durch die physikalischen Prozesse ein hoher Anteil der solaren Einstrahlung in Warme umgesetzt werden kann. Begrenzungen ergeben sich hauptsachlich durch konstruktive Rahmenbedingungen sowie materialspezifische Begrenzungen. Bei adaquater Material- und Temperaturwahl sowie konstruktiver Gestaltung lassen sich im passiven Bereich ca. 80 % an Energieumsetzung erreichen. Der Gesamtwirkungsgrad solarthermischer Systeme liegt jedoch deutlich unterhalb dieser Werte. Woran liegt dies? Eine Ursache ist der konvektive Transport des ein- oder mehrphasigen Warmetragers in den Rohrleitungen sowie in den im Solarsystem auftretenden Komponenten wie Pumpen, Ventile, Rohrleitungen und/oder Speicher, die alle verlustbehaftet sind und damit zu einer Verringerung des Wirkungsgrads fuhren.

Passive Mechanismen in der Solarenergie

Der Begriff passive Nutzung oder passive Masnahmen spielt in der modernen Solarthermie eine zentrale Schlusselrolle, ohne die ein effizienter Einsatz dieser Technologie undenkbar ware.

Large Eddy Simulations of Taylor-Görtler Instabilities in Transitional and Turbulent Boundary Layers

Free surface liquid metal targets are considered in several high power targets as a tool to produce secondary particles, since their power density exceeds material sustainable limits. Many target designs consider due to the high power deposited in the liquid a concave formed back plate in order to yield a higher boiling point. Upstream the free surface target domain the liquid metal flow is conditioned by a nozzle. However, a back-wall curvature as well as a concave shaped exit nozzle contour can lead to the occurrence of secondary motions in the flow caused by Taylor-Gortler (TG) instabilities. These motions may impact the hydrodynamic stability the flow and also lead to an undesired heat transfer from the hottest region produced within the liquid target towards the uncooled back plate. In this study, the suitability of the Large Eddy Simulation (LES) technique to simulate the formation, development and destruction TG instabilities in transitional and turbulent boundary layers was tested by comparing the simulation results with experimental data reported in literature. All comparisons exhibit a qualitative and quantitative good agreement between experimental data and numerical predictions regarding the mean flow parameters and unsteady large-scale structures caused by TG instabilities.Copyright

Experimental and Numerical Analysis of the Stability of the Vertical Water Jet with Rectangular Cross Section

This article describes experimental and numerical investigations of the stability of a water jet with a rectangular cross section aligned with the gravity field. This work focuses on the individual physical phenomena influencing the stability of the free surface jet flow like the contraction of the planar jet as well as the generation of capillary waves. In order to investigate the interaction between these two effects a series of experiments using water as model fluid are conducted in the Karlsruhe Liquid metal Laboratory KALLA at the research centre Karlsruhe. For the measurement of the cross-sectional shape of free water jet the Laser Doppler Anemometer (LDA) has been applied. Complementary to the experiments the numerical simulations have been performed using the commercially available code STAR-CD. The simulations show a reasonable agreement with the experimental measurements within the investigated parameter range.