Development and validation of a one-dimensional transient rotodynamic pump model at component scale

For reactor design and safety purposes, the French Alternative Energies and AtomicEnergy Commission (CEA) is currently working on the implementation of a predictive transienttwo-phase flow 4-quadrant rotodynamic pump model in the CATHARE-3 code (Code forAnalysis of THermalhydraulics during an Accident of Reactor and safety Evaluation). Thispaper presents the pump model and its validation in single-phase first quadrant conditions atcomponent scale. Explanations are first given on code architecture, meshing, equations to solveand how to switch from fixed frame to rotating frame and vice versa at impeller endpoints.Then, verification results in an ideal case are compared to Euler equations. Finally, validationresults on real cases including the prediction of single-phase first quadrant steady performancecurves and the simulation of a fast startup transient are presente

Simulation numérique et analyse du déclenchement et du développement des instabilités axiales dans les turbomachines (Application à un transitoire de brèche dans un réacteur nucléaire à hélium)

Le travail a porté sur le développement de modèles pour la simulation numérique des instabilités axiales dans les turbomachines multiétagées. L'élaboration d'un modèle monodimensionnel axisymétrique instationnaire de l'écoulement à l'intérieur d'une turbomachine (à l'échelle de la roue), a consisté en : la génération de corrélations ; la construction d'un modèle valable en régime transitoire ; la validation par rapport à des données expérimentales. Des modèles théoriques élémentaires, basés sur la généralisation de la théorie de Greitzer, ont également été élaborés. Ils ont renforcé la compréhension des phénomènes physiques régissant l'apparition et le développement des instabilités en quantifiant différents effets (inerties, compressibilité, seuils de performance) et en mettant en relief les phénomènes majeurs. Les modèles ont été appliqués à des configurations académiques, puis à un projet industriel innovant : un réacteur nucléaire rapide à caloporteur hélium et à cycle de Brayton.The subject of the present work was to develop models able to simulate axial instabilities occurrence and development in multistage turbomachines. The construction of a onedimensional unsteady axisymmetric model of internal flow in a turbomachine (at the scale of the row) has followed different steps : generation of steady correlations ; building of a model able to describe transient behaviour ; validation of the model in comparison of experimental results. An elementary theory has also been developed, based on a generalisation of Greitzer's model. These models have also allowed a more comprehensive description of physical phenomena at stake in instability occurence and development by quantifying various effects (inertia, compressibility, performance levels) and underlying the main phenomena. The models were applied to academic configurations, and then to an innovative industrial project : a helium cooled fast nuclear reactor with a Brayton cycle.LYON-Ecole Centrale (690812301) / SudocSudocFranceF

Modeling of a cold thermal energy storage for the flexibility of thermal power plants coupled to Brayton cycles

International audienceAs the share of variable renewable energy in the electricity generation continues to increase, electricity markets are facing significant variations of electricity prices. Thermal power plants that generate base-load electricity are not the most suitable for such markets. In the work reported here, a cold thermal energy storage coupled to a Brayton power conversion cycle for peak capacity generation is studied. Peak capacity is usually reached due to hot thermal storage, which increases the maximum temperature of the cycle. However, it is also possible to reduce the minimum temperature reached by the cycle to increase the power cycle efficiency. For this purpose, a cold thermal energy storage is used. It is designed to meet the needs of primary and secondary reserves required for grid frequency control. This typically represents a 7% power increase reached within 2 min over a time span of 15 min. A dynamic model of the entire 559MWe power plant is used to assess storage capacity, electrical power dynamics and impact on the plant. Since only 1700 m3 of chilled water are required, the results obtained are promising. The chilled water is generated either by a refrigeration system when the demand for electricity is low or by an absorption chiller operated by the waste heat generated by the Brayton cycle. In the past, important research work has been devoted to the development and deployment of large cold thermal energy storage for air conditioning. As a result, for such Brayton power cycles, it is possible to extend the time of peak power generation to several hours

Experimental study of a compact ORC for low grade heat conversion to electricity

International audienc

Etude expérimentale d’un ORC compact pour la conversion de chaleur basse température en électricité

International audienc

Experimental Study and Optimization of the Organic Rankine Cycle with Pure Novec^TM649 and Zeotropic Mixture Novec^TM649/HFE7000 as Working Fluid

The Organic Rankine Cycle (ORC) is widely used in industry to recover low-grade heat. Recently, some research on the ORC has focused on micro power production with new low global warming potential (GWP) replacement working fluids. However, few experimental tests have investigated the real performance level of this system in comparison with the ORC using classical fluids. This study concerns the experimental analysis and comparison of a compact (0.25 m3) Organic Rankine Cycle installation using as working fluids the NovecTM649 pure fluid and a zeotropic mixture composed of 80% NovecTM649 and 20% HFE7000 (mass composition) for low-grade waste heat conversion to produce low power. The purpose of this experimental test bench is to study replacement fluids and characterize them as possible replacement fluid candidates for an existing ORC system. The ORC performance with the pure fluid, which is the media specifically designed for this conversion system, shows good results as a replacement fluid in comparison with the ORC literature. The use of the mixture leads to a 10% increase in the global performance of the installation. Concerning the expansion component, an axial micro-turbine, its performance is only slightly affected by the use of the mixture. These results show that zeotropic mixtures can be used as an adjustment parameter for a given ORC installation and thus allow for the best use of the heat source available to produce electricity

Modelling of a Centrifugal Pump Using the CATHARE-3 One-dimensional Transient Rotodynamic Pump Model

International audienceThe CATHARE-3 predictive transient rotodynamic pump model and its validation in single-phase first quadrantconditions at component scale are presented in this paper. One-dimensional discretization and resolution of governingequations are made according to a mean flow path along all pump parts (suction, impeller, diffuser, volute and dischargepipe), what makes the model original compared to classical 1D models. The model is first verified by comparison to theEuler equation of turbomachinery results. Then, qualification of the model is carried out in steady and transient conditionsby comparison to available experimental data. Head and torque characteristics curves are well predicted at differentrotational speeds. Finally, a fast startup transient is simulated. Results are satisfactory as the difference between theexperimental and modelled non-dimensionalized head is less than 10% of the final value during the whole startup

Simulation of a Radial Pump Fast Startup and Analysis of the Loop Response Using a Transient 1D Mean Stream Line Based Model

International audienceA predictive transient two-phase flow rotodynamic pump model has been developed in the Code for Analysis of THermalhydraulics during an Accident of Reactor and safety Evaluation (CATHARE-3). Flow inside parts of the pump (suction, impeller, diffuser and volute) is computed according to a one-dimensional discretisation following a mean flow path. Transient governing equations of the model are solved using an implicit resolution method and integrated along the curvilinear abscissa of the element. This model has been previously qualified at the component scale by comparison to an existing experimental database. The present study aims at extending the validation at the system scale: a whole experimental test loop is modelled. The ability of the transient pump model to predict flow rate, head and torque as a function of time during a 1-s pump fast start-up is evaluated. The transient evolution of the pressure upstream and downstream from the centrifugal pump is well predicted by the simulation compared to the measurements. Local quantities such as pressure and velocity inside elements of the circuit are analysed. In the considered case, inertial effects of the global circuit are dominant when compared to pump inertial effects due to the high characteristic lengths of the pipes. The main perspective of this work consists in the simulation of similar pump transients, in cavitating conditions

On the dynamic modeling of Brayton cycle power conversion systems with the CATHARE-3 code

International audienceAs the share of intermittent energy sources is increasing, the dynamic modeling of thermal power plants including their power conversion system gets researchers' attention. Recent applications require transient simulations of high-pressure nitrogen closed Brayton cycle for which the ideal gas assumption is no longer verified. In this work, the REFPROP real gas equation of state and pressure drop correlations suitable for high Reynolds numbers have been implemented in the CATHARE-3 code. Moreover, new real gas turbomachinery and sonic flow models have been developed and integrated in the code. Relative errors obtained for the nominal state of a high-pressure nitrogen closed Brayton cycle are in the range −3%/+0.8%. A detailed analysis of real gas effects is carried out on the heat exchangers heat flux and the piping pressure losses. The new sonic flow computed during a loss of coolant accident is in the best possible agreement with literature experimental results. With regard to the turbomachinery, the new real gas model creates a pressure dependence that brings compressors closer to the choke region when the pressure drops in the cycle. This work is expected to provide an efficient and reliable simulation tool for transient analysis of real gas closed Brayton cycles