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- ItemA beam window target design with independent cooling for the EADF(2000-11-30) Aragonese, Cosimo; Buono, Stefano; Fotia, Giorgio; Maciocco, Luca; Moreau, Vincent; Sorrentino, LucaThis report summarizes the study and the design of the window type target for the Energy Amplifier Demonstration Facility (EADF) [1]. The behaviour of the system in different condition has been analysed though extensive CFD simulations performed with the Star-CD commercial code [2]. The target represents one of the main technological problems related not only to the design of the EADF, but to all High Power Spallation Sources (HPSS) currently under study or in construction world-wide [4],[5]. Different configurations of the spallation EADF target are possible. Advantages and disadvantages of the different options are discussed elsewhere [6] and they are studied and analysed separately. The target device studied in this report is a window type target, cooled by diathermic oil in an independent loop. This target configuration is completely independent from the core operating conditions and gives advantages in terms of flexibility in the operation. The result of this report is a set of design data and constraints to take into account while engineering the spallation target.
- ItemA heat exchanger design for the separated window target of the EADF(2000) Aragonese, Cosimo; Buono, Stefano; Fotia, Giorgio; Maciocco, Luca; Moreau, Vincent; Sorrentino, LucaThe spallation target of the Energy Amplifier Demonstration Facility (EADF) [1] is cooled by a liquid lead-bismuth eutectic (LBE), while the secondary coolant is a diathermic oil. The reasons for these choices have been extensively discussed in [2] and [3]. Here we present the design and the optimisation of a heat exchanger using these fluids, whose additional requirements are the need of fitting into the top of the annular downcomer section of the target and the minimisation of the pressure losses on the LBE side, allowing the use of natural convection for the circulation of the primary fluid. Heat exchanger working temperatures are between 250 and 180°C in the LBE side, and between 150 and 190°C in the oil side (cold fluid), while the power to be removed is up to 3 MW. We selected a bayonet-type heat exchanger, as suggested in [4] for the primary loop of the EADF vessel, which seems to be the most appropriate choice to satisfy all the requirements.
- ItemA thermal fluid-dynamic steady state analysis of the EADF downcomer channel(2000-04-04) Aragonese, Cosimo; Buono, Stefano; Fotia, Giorgio; Maciocco, Luca; Moreau, Vincent; Sorrentino, LucaIn this work a numerical simulation of the Energy Amplifier Demonstration Facility (EADF) [1, 2] downcomer channel is presented. The simulation is fully three-dimensional (3D) and is focused on a Steady-State Analysis. All relevant heat transfer phenomena are taken into account. The Intermediate Heat eXchangers (IHX) of the EADF reference configuration are immersed in the lead-bismuth eutectic of the downcomer and no physical barrier separates the hot and cold collectors. As expected, the simulation shows a thermal stratification outside the IHX, whose characteristics mainly depend on the IHX pressure loss. A parametric study of the effects of the IHX pressure loss coeficient on the thermal stratification pattern is presented.
- ItemA thermal fluid-dynamic transient analysis of the EADF down-comer channel(2000-12-05) Aragonese, Cosimo; Buono, Stefano; Fotia, Giorgio; Maciocco, Luca; Moreau, Vincent; Sorrentino, LucaIn this work a numerical simulation of the downcomer channel of the Energy Amplifier Demonstration Facility (EADF) [1, 2] is presented. The simulation is fully three-dimensional (3D) and is focused on a transient analysis. All relevant heat transfer phenomena are taken into account. Starting from the nominal power configuration, we have simulated the response of the system to a power shutdown of the core for a period of 60 s. The core shutdown is simulated imposing a linear variation of the inlet flow temperature from 400°C to 305°C in 10 s. The simulation shows the evolution of the thermal stratification outside the IHX and the evolution of the IHX operation.
- ItemAnalysis and optimisation of a gas-cooled pipe for solar thermal energy production using parabolic collectors(2000-03) Aragonese, Cosimo; Buono, Stefano; Maciocco, Luca; Moreau, Vincent; Sorrentino, LucaIn the framework of the design of a solar thermal power plant proposed by ENEA, the activity carried out by CRS4 on the thermal-fluid-dynamic simulation of a gas-cooled pipe irradiated by a parabolic solar collector is described in this paper. Two methods have been adopted in parallel: a simplified one-dimensional approach and a Computational-Fluid-Dynamics (CFD) three-dimensional approach. The first method was used to build a tool able to give quick answers to parameters changes with an acceptable degree of accuracy. The CFD analysis is used both to validate 1D-model results and to study in details all 3D physical phenomena. The multi-zone one-dimensional model developed at CRS4 is described first. The pipe is split along its axis into a discrete number (typically 100) of sub-domains. Each sub-domain is split further on into five different zones, corresponding to the various components of the pipe. All the main energy-exchange mechanisms between the various parts of the pipe have been implemented, resulting in a system of five equations for each sub-domain, solved iteratively within an EXCEL framework. The 3D-CFD model is then described. The model is fully parametric, allowing a quick variation of the geometrical parameters of the system. Convection, conduction and thermal radiation heat exchanges are solved in a coupled way. The model can give any information about field variables of fluids and solid structures as well as all energy balances. The two models have been used for a parametric study of the effect of the pipe diameter variation on the system efficiency. Although not negligible differences between the two models can be noticed concerning local energy balances, the error on the evaluation of the system efficiency is order 1%. The result of the optimization was practically the same for the two models.
- ItemCFD simulation of a heated round jet of sodium in forced flow regime (TEFLU benchmark)(2000-11-17) Aragonese, Cosimo; Buono, Stefano; Fotia, Giorgio; Maciocco, Luca; Moreau, Vincent; Sorrentino, LucaThe results of the simulation of the forced-flow case of the TEFLU benchmark [1], obtained at CRS4 with the Star-CD code, are reported. First, a comparison among different k-ε turbulence models implemented in Star-CD was carried out. The Chen k-ε model [4], [5] gave the best agreement with experimental results. Then, a study of the influence of the turbulent Prandtl number Prt was carried out. The first step was the comparison between the molecular conductivity and the turbulent heat diffusion coefficients, calculated using the turbulent Prandtl number approach (Reynolds analogy). It was found that that the two contributions are of the same order of magnitude. This result implies that there is a strong interaction between the molecular and turbulent heat transfer, which could have a strong effect on the scaling coefficient between the turbulent transfer of momentum and heat, namely on Prt. In order to study the effect of the variation of Prt on the temperature profiles, the inlet turbulence kinetic energy profile was scaled in order to obtain a good agreement between calculated and experimental velocity profiles. Then, the value of Prt was changed from the standard value of 0.9 to 10 (on the basis of the considerations of Jisha and Rieche [6]) and to 104 (to exclude the contribution of the turbulent heat transfer). A very good agreement with experimental measurements was found in both cases (the best being the case of no turbulent heat transfer). The above results indicate that the heat conduction is predominant in the forced-flow case. In this situation, the standard value 0.9 of Prt yields an overestimation of the thermal diffusion rate.
- ItemMixing influence on ε-caprolactam quality: an industrial application of CFD simulation(1999) Santucciu, P.; Aragonese, Cosimo; Andrigo, P.; Rame, k.CPL production is a mixing sensitive system and for this reason it is used as test case for a CFD code including micromixing phenomena description. The code CFX-4 is used for simulating the behaviour of a rotor-stator mixer, considered as a reactor. Specific properties like kinetic laws and viscosity functions have been experimentally estimated and here reported. The preliminary results of fluid dynamic validation are here reported.
- ItemMonitoring of a CO oxidation reactor through a grey model-based EKF observer(2000) Porru, Gianfranco; Aragonese, Cosimo; Baratti, RobertoOften, in real applications it is difficult to dispose of a simple, yet, representative kinetic model because of the complexity of the reactions taking place. To overcome this limitation a hybrid modelling approach is proposed for the identification of the dynamic behaviour of chemical reactors. In particular, the tools of neural network modelling have been exploited to represent the kinetic reaction data. The "neural reaction rate model" is integrated within a first principles model that constitutes the basis of a nonlinear observer (Extended Kalman Filter, EKF) for an etherogeneus gas-solid reactor where the catalytic oxidation of carbon monoxide take place. The outlined procedure shows that artificial neural networks (ANN) can be effectively used to formulate lumped reaction rates because of their capability in capturing the essential characteristics of the functional relationship among the state variables.
- ItemStructural response of the EADF target beam window to beam interruptions: transient thermo-mechanical computation(1999) Aragonese, Cosimo; Maciocco, Luca; Bellucci, Valter; Buono, Stefano; Fotia, Giorgio; Moreau, Vincent; Siddi, Giuliana; Sorrentino, LucaThe operability of a high power proton beam target in an Accelerator Driven System (ADS) is strictly connected to the structural integrity of the beam window, which is undoubtedly the most delicate component in such devices, being exposed to the combined effects of high intensity proton and neutron irradiation, liquid metal corrosion and high thermal stresses induced by the interaction with the beam. It has also recently been highlighted that beam trips may frequently occur in current high power accelerators [1]. Clearly, the definition of the requirements of future accelerators depends on the behaviour of the window under such conditions. For this purpose a numerical study of typical transients has been carried out on the 600 MeV proton beam target that drives the 80 MW Demonstration Facility of the Energy Amplifier proposed by C. Rubbia, [2] presently under development in Italy by Ansaldo, CRS4, ENEA and INFN [3].
- ItemThermal analysis of the TOF lead target at CERN(2001-03-16) Aragonese, Cosimo; Buono, Stefano; Maciocco, Luca; Moreau, Vincent; Sorrentino, LucaThe lead target at the Time Of Flight (TOF) facility at CERN, currently under commissioning, undergoes relevant temperature transients due to the intensity of the four 20 GeV/c pulses of 7 x 1012 protons, carrying an energy of 21.4 kJ delivered in 7 ns each. A 3D thermal analysis of the target system in both steady-state and transient conditions has been performed using the finite volume commercial code StarCD coupled with the results from Fluka simulations. Results show that the maximum temperature inside the lead target using the parameters of the TOF commissioning phase (4 pulses every 1.2 s in a 14.4 s super-cycle) is 127°C at steady-state operations, which is an acceptable value, compatible with safe and durable target operations. A significant improvement could be obtained by doubling the beam size (108°C maximum temperature in the bulk of the central block). The transients coming from the pulsed operation are not such as to create structural problems related to thermal fatigue. It is interesting to notice that the thermal oscillation in the hottest point in the bulk of the central block is much lower in the case where the 4 pulses are spaced of 3.6 s during the PS super-cycle (about 20°C), than in the case where they are spaced of only 1.2 s (about 40° C).