1,721,004 research outputs found
Thermodynamic Analysis of High-Temperature Energy Storage Concepts Based on Liquid Metal Technology
Full text linkWithin the thermal energy storage (TES) initiative NAtional Demonstrator for IseNtropic Energy storage (NADINE), three projects have been conducted, each focusing on TES at different temperature levels. Herein, technical concepts for using liquid metal technology in innovative high-temperature TES systems are dealt with. This approach implies some challenges; first, the unit costs are relatively large which makes a reduction of the mass inventory necessary. Second, the high thermal diffusivity, which is beneficial in any heat exchanger unit, reduces the efficiency in a single-tank TES due to the fast degradation of the thermocline. These limitations can be overcome using a nonexpensive solid filler material, and, if properly designed, similar performance as in state-of-the-art molten salt systems can be obtained, while maintaining the advantage of operating at temperatures well beyond their upper limit. Optimization strategies are presented for a reference case including transient behavior of the whole system. The sensitivity of multiple parameters, e.g., porosity, particle size, and influence of storage capacity regarding the discharge efficiency, is investigated
Heat transfer to liquid metals in a hexagonal rod bundle with grid spacers: Experimental and simulation results
Full text linkThermal-hydraulics is a key scientific subject to be investigated for the development of innovative reactor systems. For applications using liquid metals as coolants this task is particularly challenging due to their very low Prandtl number (Pr), preventing the application of common analogies between the turbulent transport of momentum and heat. Thus specific models and validation data with low-Pr fluids are required for representing safety-related thermal-hydraulic scenarios, such as heat transfer in fuel assemblies. Aiming to achieve a better understanding of these flow scenarios, in the European FP7 cooperation project THINS (2010-2014) this subject is investigated at three complementary levels. An experimental campaign consisting of an electrically heated 19-pin hexagonal rod bundle cooled by lead-bismuth eutectic (LBE) is carried out at typical reactor conditions in terms of operating temperature, power density and velocity. Both pre- and post-test analyses using existing numerical tools are performed for evaluating the differential pressure and heat transfer characteristics of the test section. Moreover, advanced turbulence models and numerical techniques are developed and applied to this geometry. Overall, the goals of this project are achieved. The experiments show good degree of repeatability and provide reliable validation data. For intermediate flow rates a good agreement is observed with the results of the heat transfer simulations, based on a constant turbulent Prandtl number. Two advanced approaches for representing the turbulent heat transport considering look-up tables and a four-equation model are successfully tested and overcome the limitations of using a constant turbulent Prandtl number. Using a coarse-grid CFD approach the turbulent momentum transport along two bundles is studied, yielding a good accuracy with a 1000-fold mesh reduction
Experimental activities at KALLA on heavy-liquid metal heat transfer for fast reactors
No full textHeavy liquid metals (HLMs), such as lead-bismuth eutectic (LBE) and pure lead are prominent candidate coolants for fast neutron systems, both critical assemblies and accelerator-driven systems. One of the key questions for the safety of these systems is the fundamental understanding of thermal-hydraulic aspects, such as the cooling of fuel assemblies under normal and accidental conditions. For several reasons, this problem is particularly challenging, compared to reactors cooled with conventional coolants. Extensive efforts are currently devoted worldwide to improving the understanding of these flows. Reliable experimental data are essential for developing advanced predicting models, but scarce. This issue has been experimentally investigated at the Karlsruhe Liquid Metal Laboratory KALLA for over a decade, in a comprehensive series of experiments of progressively increasing complexity. This contribution presents the main results from these experiments, e.g. heat transfer correlations, local temperature distributions in the fluid as well as in the rod cladding. Lessons learned in view of the experimental setup, instrumentation, procedures and usefulness of the results for development and validation of simulation codes are also presented. Finally, the main open issues which require further research are identified
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Thermal-Hydraulic Experimental Testing of the MYRRHA Wire-Wrapped Fuel Assembly
No full textIn recent years, extensive thermal-hydraulic experimental tests have been performed on the lead-bismuth eutectic (LBE)–cooled, wire-wrapped fuel assembly (FA) of MYRRHA. These thermal-hydraulic tests were performed using FA mock-ups in large-scale LBE experimental test facilities at SCK•CEN (Belgium), ENEA (Italy), and Karlsruhe Institute of Technology (Germany). The FA pressure drop characteristics and flow-induced vibration (FIV) characteristics were tested with a full-scale 127-pin mock-up test section. The existing pressure drop correlations of Rehme and of Cheng and Todreas (simplified model) predict the experimental pressure drop data very well and are considered suitable for use in the design and safety analysis of the MYRRHA system. FIVs are very limited in the wire-wrapped bundle, and fuel pin fatigue damage from vibration during operation is not expected. Further analysis and testing are required to determine if damage from fretting corrosion could be expected. Heat transfer characteristics of the FA were investigated experimentally in two separate 19-pin heated rod test sections cooled by LBE. The existing Kazimi-Carelli correlation predicts the global average Nusselt numbers very well, but the correlation is not developed to capture local hot spots. For the FA safety analysis, to further determine operational safety margins, a hot-spot factor is defined and analyzed to determine the hot-spot temperature penalty
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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