1,721,180 research outputs found
Experimental campaign on the HLM loop NACIE-UP with instrumented wire-spaced fuel pin simulator
No full textThis work reports post-processed data of the experimental campaign carried out in the HLM-operated NACIE-UP facility in the framework of the HORIZON2020 SESAME project. NACIE-UP is a rectangular loop, where the two vertical pipes, which work as riser and downcomer, are 8 m long and the two horizontal pipes are 2.4 m long. A prototypical MYRRHA-like wire-spaced fuel pin bundle simulator (FPS) is installed in the bottom part of the riser, whereas a shell and tubes heat exchanger (HX) is placed in the upper part of the downcomer. The difference in height between the centre of the heating section and the centre of the heat exchanger is about 5.5 m and is essential for the establishment of the natural circulation regime inside the loop. A typical PLOFA test is presented in this paper, from the three fundamental tests performed. Temperatures showed a coherent behaviour with a sharp decrease due to the power decrease from about 100 kW to 10 kW followed by local maximum due to the gas-lift stop. The time trend of the main thermal-hydraulic parameters during the transient are illustrated in detail: among the others, there is the curve of the primary coolant flow rate, measured by a prototypical thermal flow meter. In the FPS, the developing thermal field was experimentally proved, with larger radial differences in the temperature distribution at the outlet monitored sections with respect to the inlet monitored one. Nusselt numbers in the fully developed section exhibited values close to the Kazimi-Carelli correlation and a similar trend. On the initial and final steady states, a statistical analysis was carried out to determine average overall and local values, and the associated uncertainties. The error propagation theory was applied for the derived quantities. Lots of data, both integral and local, were produced and published; the aim is that this information can be used to qualify STH codes, verify CFD codes and coupled STH/CFD methods for HLM systems. © 201
CFD pre-test analysis of the fuel pin bundle simulator experiment in the NACIE-UP HLM facility
No full textIn the context of the studies on GEN. IV/ADS nuclear systems, the correct evaluations of the temperature distribution in the fuel pin bundle is of central interest. In particular, the use of lead or lead-bismuth eutectic (LBE) as coolant for the new generation fast reactors is one of the most promising choices. At ENEA-Brasimone R.C., large experimental facilities exist to study HLM free, forced and mixed convection in loops and pools: e.g. NACIE-UP is a large scale LBE loop for mixed convection experiments. In the context of the SEARCH FP7 project, an experiment has to be performed in the NACIE-UP facility to assess the coolability of a 19-pin wire-wrapped electrical bundle (Fuel Pin Simulator, FPS), with heat flux up to 1 MW/m2. The bundle is representative of the one adopted in the MYRRHA concept. A CFD analysis of fluid flow and heat transfer was carried out in the heavy liquid metal (LBE) cooled bundle test section of the NACIE-UP facility. The model includes the details of the wire-spacers as well as the entry region of the test section. A turbulence closure approach is adopted for all the simulations with = 3.5-107 nodes and a resolution of y+ = 1 - 4 at the wall in the range of interest. Results are compared with the up-to-date correlations on pressure loss and heat transfer and the experimental range is completely explored by CFD. The thermal structures of the test section are modelled and the role of conjugate heat transfer was assessed. Several highlights emerged from the numerical study for the experimental campaign. In particular, the accuracy in the measurement of heat transfer between rods and fluid was evidenced as weak point of the experimental test matrix. As a consequence the test matrix was modified. Copyright © (2015) by American Nuclear Society All rights reserved
Turbulence structure and budgets in curved pipes
No full textTurbulent flow in curved pipes was investigated by Direct Numerical Simulation. Three curvatures δ (pipe radius a/curvature radius c) were examined: δ=0 (straight pipe), simulated for validation and comparison purposes; δ=0.1; and δ=0.3. The friction velocity Reynolds number (based on the pipe radius a) was 500 in all cases, yielding bulk Reynolds numbers of ~17,000, ~15,000 and ~12,000 for δ=0, 0.1 and 0.3, respectively. The computational domain was ten pipe radii in length and was resolved by up to 20×106 hexahedral finite volumes. The time step was chosen equal to a wall time unit; 1 Large Eddy TurnOver Time (LETOT) was thus resolved by 500 time steps and simulations were typically protracted for 20 LETOT's, the last 10 being used to build turbulence statistics and budgets.In curved pipes, time mean results showed Dean circulation and a strong velocity stratification in the curvature direction, as in laminar flow; turbulent fluctuations were highest in the outer bend region, whereas the flow near the inner wall was almost laminar. Significant turbulence levels were confined to a near-wall layer narrower than in the straight pipe. Near-wall streamwise velocity and wall shear stress exhibited the streak structure typical of turbulent channel flows only along the outer wall, while on the inner wall they exhibited a flat and low-level distribution. As the curvature increased, fluctuations in the plane of the cross section increased in intensity, following the trend of the time mean secondary flow, whereas axial (streamwise) fluctuations became weaker. Overall turbulence levels decreased with the curvature and were lower in a curved pipe than in the straight pipe. Turbulence budgets over the cross section confirmed that in curved pipes production and other budget terms are comparable with those in the straight pipe (or even higher) in the outer bend region, whereas they rapidly decay as one moves towards the inner side. They also indicated that, in curved pipes, convection terms play a significant role in the turbulence budget, especially in the regions of the Dean vortices. © 2013 Elsevier Ltd
Progettazione preliminare di una pompa centrifuga per l'impianto a metallo liquido pesante HELENA
Full text linkL'attività descritta nel presente documento si inserisce all'interno del progetto HELENA, che si pone come obiettivo globale la progettazione e successiva realizzazione di una pompa centrifuga monostadio con voluta, destinata alla movimentazione di metallo liquido pesante. Lo svolgimento del progetto in questione è suddivo in quattro fasi distinte, di seguito brevemente illustate: fase 1: attraverso lo sviluppo di un codice di calcolo monodimensionale, si valutano le prestazioni idrauliche della pompa in funzione di un ampio spettro di parametri geometrici di progetto; il codice è infine interfacciato all'ottimizzatore allo scopo di far guidare da meccanismi evolutivi la scelta dei parametri progettuali sulla base delle prestazioni misurate dalle funzioni obiettivo; fase 2: si svolge un'ottimizzazione delle prestazioni idrauliche della girante attraverso una campagna di simulazioni numeriche tridimensionali, time-dependent, su rotating grid, allo scopo di affinare i profili palari della girante, la conformazione del canale meridiano e della voluta in relazione ai parametri di valutazione (obiettivi generali e indicatori locali di prestazione); fase 3: si procede alle verifiche strutturali di carattere ingegneristico dei principali organi componenti la pompa, al fine di valutare la stabilità di funzionamento e la durata; fase 4: si esegue la modellazione CAD tridimensionale della pompa, con i relativi disegni costruttivi, necessari alla produzione industriale della pompa
Pre-test CFD simulations of the NACIE-UP BFPS test section
No full textthe conjugate heat transfer in the clad is also considered. The blockages investigated are internal blockages of different extensions and in different locations: central sub-channel blockage, corner sub-channel blockage, edge sub-channel blockage, one sector blockage, and two-sector blockage. RANS simulations were carried out adopting the ANSYS CFX commercial code with the laminar sublayer resolved by the mesh resolution. The loci of the peak temperatures and their width as predicted by the CFD simulations are used for determining the location of the pin bundle instrumentation. The CFD pre-test analysis allowed also investigating the temperature distribution in the clad to operate the test section safely. © 2017 Elsevier LtdThe present paper is focused on the CFD pre-test analysis and design of the new experimental facility ‘Blocked’ Fuel Pin bundle Simulator (BFPS) that will be installed into the NACIE-UP (NAtural CIrculation Experiment-UPgrade) facility located at the ENEA Brasimone Research Center (Italy). The BFPS test section will carry out suitable experiments to fully investigate different flow blockage regimes in a 19 fuel pin bundle providing experimental data in support of the development of the ALFRED (Advanced Lead-cooled Fast Reactor European Demonstrator) LFR DEMO. The geometrical domain of the fuel pin bundle simulator was designed to reproduce the geometrical features of ALFRED, e.g. the external wrapper in the active region and the spacer grids. Pre-tests calculations were carried out by applying accurate boundary condition
Coupled simulations of the NACIE facility using RELAP5 and ANSYS FLUENT codes
No full textThis work deals with the development and preliminarily assessment of a coupling methodology between a modified version of RELAP5/Mod3.3 STH code and FLUENT commercial CFD code, applied to the NACIE (natural circulation experiment) LBE (lead bismuth eutectic) experimental loop (built and located at the ENEA Brasimone research centre). The coupling tool is used to simulate experiments representative of both natural circulation conditions and isothermal gas enhanced (assisted) circulation. Furthermore, an accidental test reproducing an Unprotected Loss of Flow (ULOF) scenario is also simulated and the outcomes are presented. A preliminary sensitivity analysis has shown that, to guarantee a suitable numerical convergence, the assisted circulation tests require a time step one order of magnitude lower compared to natural circulation ones. The comparison between the RELAP5 stand-alone simulations and RELAP5/FLUENT coupled simulations proved the capability to simulate the thermal-hydraulic behaviour of a loop experimental facility for all the examined conditions. © 2016 Elsevier Lt
CFD analyses of the internal blockage in the nacie-up fuel Pin Bundle simulator
No full textIn the context of GEN-IV heavy liquid metal-cooled reactors safety studies, the flow blockage in a fuel sub-assembly is considered one of the main issues to be addressed and one of the most important accidents for Lead Fast Reactors (LFR). In order to model the temperature and velocity field inside a wrapped fuel assembly under unblocked and blocked conditions, a detailed experimental campaign as well as 3D thermal hydraulic analyses of the fuel assembly are required. The present paper is focused on the CFD modeling and preliminary computational analysis of the new experimental facility „Blocked‟ Fuel Pin bundle Simulator (BFPS) that will be inserted in the heavy liquid metal NACIE-UP (NAtural CIrculation Experiment-UPgrade) facility located at the ENEA Brasimone Research Center (Italy). The BFPS test section aims to carry out suitable experiments to fully investigate different flow blockage regimes in a 19-pin fuel bundle providing experimental data in support of the development of the ALFRED (Advanced Lead-cooled Fast Reactor European Demonstrator) LFR DEMO. The BFPS test section, LBE cooled, was conceived with a thermal power of about 250 kW and a wall heat flux up to 0.7 MW/m2, which are relevant values for a LFR. It consists of 19 grid-spaced electrical pins placed on a hexagonal lattice with a pitch to diameter ratio of 1.4 and a diameter of 10 mm. The geometrical domain of the fuel pin bundle simulator was designed to reproduce the geometrical features of ALFRED, e.g. the external wrapper in the active region and the spacer grids. Different modeling approaches (e.g. meshing, turbulence modeling, codes and users) in RANS, URANS and LES will be compared to each other. The pre-test analyses presented here will facilitate the post-test analysis of the experimental data expected in 2017-2018. These calculations were carried out by applying unambiguous boundary conditions. In addition conjugate heat transfer is also considered. The comparison among different codes and turbulence models allows to make an overall assessment of different approaches to CFD modeling and simulation. ANSYS CFX, STAR-CCM+ and OpenFOAM simulations are compared to each other. © 2016 Association for Computing Machinery Inc. All Rights Reserved
Progettazione e realizzazione di un pin bundle per l'investigazione dello scambio termico in regime di convezione mista in sistemi LFR
Full text linkIl presente documento presenta la progettazione e realizzazione di un pin bundle con filo separatore da utilizzare in future campagne sperimentali ad ENEA Brasimone. Inoltre viene presentato un modello analitico-empirico per il computo delle principali grandezze integrali in NACIE ed un modello 3D CFD del pin bundle in metallo liquido fluente
STH-CFD codes coupled calculations applied to HLM loop and pool systems
No full textThis work describes the coupling methodology between a modified version of RELAP5/Mod3.3 and ANSYS Fluent CFD code developed at the University of Pisa. The described coupling procedure can be classified as "two-way," nonoverlapping, "online" coupling. In this work, a semi-implicit numerical scheme has been implemented, giving greater stability to the simulations. A MATLAB script manages both the codes, oversees the reading and writing of the boundary conditions at the interfaces, and handles the exchange of data. A new tool was used to control the Fluent session, allowing a reduction of the time required for the exchange of data. The coupling tool was used to simulate a loop system (NACIE facility) and a pool system (CIRCE facility), both working with Lead Bismuth Eutectic and located at ENEA Brasimone Research Centre. Some modifications in the coupling procedure turned out to be necessary to apply the methodology in the pool system. In this paper, the comparison between the obtained coupled numerical results and the experimental data is presented. The good agreement between experiments and calculations evinces the capability of the coupled calculation to model correctly the involved phenomena. © 2017 M. Angelucci et al
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