Estudio del comportamiento de la película de líquido en flujo anular aire-agua vertical ascendente al variar la tensión superficial mediante mezclas agua-1-butanol

[ES] El documento recoge el estudio llevado a cabo en la instalación VAFF (Vertical Anular Flow Facility) donde se estudia el comportamiento del régimen de flujo anular vertical ascendente aireagua. Se han llevado a cabo un conjunto de tests con un rango de caudales de aire de 2000 ¿ 3500 l/min y de agua de 4 ¿ 7 l/min. Estos tests se han repetido un total de cuatro veces variando la proporción de 1-butanol que se le adiciona al agua con objeto de variar su tensión superficial manteniendo prácticamente inalteradas el resto de propiedades. De esta forma las tensiones superficiales obtenidas fueron de 72·10-3 , 68.5·10-3 , 55·10-3 y 45·10-3 N/m. En el documento se muestran algunos de los resultados, así como el error cometido.Los autores quieren agradecer el apoyo de la Agencia Nacional de Investigación de España al proyecto EXMOTRANSIN, ENE2016-79489-C2-1-P.Rivera-Durán, Y.; Muñoz-Cobo, JL.; Cuadros, J.; Berna, C.; Escrivá, A.; Iglesias, SM.; Domínguez, DS. (2019). Estudio del comportamiento de la película de líquido en flujo anular aire-agua vertical ascendente al variar la tensión superficial mediante mezclas agua-1-butanol. Sociedad Nuclear Española. 1-8. http://hdl.handle.net/10251/180951S1

A CFD-DEM solver to model bubbly flow. Part I: Model development and assessment in upward vertical pipes

[EN] In the computational modeling of two-phase flow, many uncertainties are usually faced in simulations and validations with experiments. This has traditionally made it difficult to provide a general method to predict the two-phase flow characteristics for any geometry and condition, even for bubbly flow regimes. Thus, we focus our research on studying in depth the bubbly flow modeling and validation from a critical point of view. The conditions are intentionally limited to scenarios where coalescence and breakup can be neglected, to concentrate on the study of bubble dynamics and its interaction with the main fluid. This study required the development of a solver for bubbly flow with higher resolution level than TFM and a new methodology to obtain the data from the simulation. Part I shows the development of a solver based on the CFD-DEM formulation. The motion of each bubble is computed individually with this solver and aspects as inhomogeneity, nonlinearity of the interfacial forces, bubble-wall interactions and turbulence effects in interfacial forces are taken into account. To develop the solver, several features that are not usually required for traditional CFD-DEM simulations but are relevant for bubbly flow in pipes, have been included. Models for the assignment of void fraction into the grid, seeding of bubbles at the inlet, pressure change influence on the bubble size and turbulence effects on both phases have been assessed and compared with experiments for an upward vertical pipe scenario. Finally, the bubble path for bubbles of different size have been investigated and the interfacial forces analyzed. (C) 2017 Elsevier Ltd. All rights reserved.The authors sincerely thank the ''Plan Nacional de I + D+ i" for funding the project MODEXFLAT ENE2013-48565-C2-1-P and ENE2013-48565-C2-2-P.Peña-Monferrer, C.; Monrós Andreu, G.; Chiva Vicent, S.; Martinez-Cuenca, R.; Muñoz-Cobo, JL. (2018). A CFD-DEM solver to model bubbly flow. Part I: Model development and assessment in upward vertical pipes. Chemical Engineering Science. 176:524-545. https://doi.org/10.1016/j.ces.2017.11.005S52454517

Role of age and comorbidities in mortality of patients with infective endocarditis

Purpose: The aim of this study was to analyse the characteristics of patients with IE in three groups of age and to assess the ability of age and the Charlson Comorbidity Index (CCI) to predict mortality. Methods: Prospective cohort study of all patients with IE included in the GAMES Spanish database between 2008 and 2015. Patients were stratified into three age groups:<65 years, 65 to 80 years, and = 80 years.The area under the receiver-operating characteristic (AUROC) curve was calculated to quantify the diagnostic accuracy of the CCI to predict mortality risk. Results: A total of 3120 patients with IE (1327 < 65 years;1291 65-80 years;502 = 80 years) were enrolled.Fever and heart failure were the most common presentations of IE, with no differences among age groups.Patients =80 years who underwent surgery were significantly lower compared with other age groups (14.3%, 65 years; 20.5%, 65-79 years; 31.3%, =80 years). In-hospital mortality was lower in the <65-year group (20.3%, <65 years;30.1%, 65-79 years;34.7%, =80 years;p < 0.001) as well as 1-year mortality (3.2%, <65 years; 5.5%, 65-80 years;7.6%, =80 years; p = 0.003).Independent predictors of mortality were age = 80 years (hazard ratio [HR]:2.78;95% confidence interval [CI]:2.32–3.34), CCI = 3 (HR:1.62; 95% CI:1.39–1.88), and non-performed surgery (HR:1.64;95% CI:11.16–1.58).When the three age groups were compared, the AUROC curve for CCI was significantly larger for patients aged <65 years(p < 0.001) for both in-hospital and 1-year mortality. Conclusion: There were no differences in the clinical presentation of IE between the groups. Age = 80 years, high comorbidity (measured by CCI), and non-performance of surgery were independent predictors of mortality in patients with IE.CCI could help to identify those patients with IE and surgical indication who present a lower risk of in-hospital and 1-year mortality after surgery, especially in the <65-year group

Type II instabilities in advanced heavy water natural circulation reactors: Application to the AHWR

[EN] This paper deals with the instabilities in advanced heavy water reactors driven by natural circulation at high pressure and power conditions. This paper also study which are the design and operating parameters that have more influence on the appearance of type II instabilities. Some of the results are compared with usual BWR reactors to stablish which are the differences between both types of reactors in the development of limit cycle oscillations and the maximum amplitude values of these oscillations when some of the influential parameters on the stability are changed. This paper also explains the main characteristics of the modelling used to simulate the fuel channels, the risers or outlet feeders, the recirculation loop of this reactor, and the kinetic and heat transfer models. In addition, we compare the closure relations used in this model with the experimental correlations for the AHWR, to know the applicability of the correlations for the AHWR under natural circulation conditions. Finally, we study in this paper the influence on the decay ratio (DR) and the limit cycle amplitude of a set of design and operational parameters. Some of these parameters are: the amount of coolant direct heating by neutrons and gamma-rays, the form loss coefficient at the channel inlet, the form loss coefficient in the spacers, the phase change number No, the characteristic natural circulation time and the effective inertia of the recirculation loop.The authors of this paper are indebted to the help received for the MINECO grant ENE2016-79489-C2-1-P and to the Bhabba Atomic Center, specially to Dr Vijayan for give us the opportunity to review the PH.D. Thesis of Mr. Sapna Singh.Muñoz-Cobo, J.; Escrivá, A.; Berna, C. (2019). Type II instabilities in advanced heavy water natural circulation reactors: Application to the AHWR. Progress in Nuclear Energy. 117:1-13. https://doi.org/10.1016/j.pnucene.2019.103056S11311

Obtencion de las soluciones periodicas de un oscilador no lineal mediante un método rapido de Galerkin

Este artículo está enfocado a la determinación de las soluciones periódicas de los osciladores no lineales así como al análisis cualitativo de su estabilidad. En este trabajo desarrollamos un algoritmo basado en el método de Galerkin que utiliza la transformada rápida de Fourier (FFT) para calcular las soluciones periódicas de la ecuación anterior. Además, incluimos un algoritmo combinado en un apéndice, con convergencia rápida, para resolver las ecuaciones algebraicas no lineales obtenidas por dicho método. Finalmente, validamos esta metodología aplicando el algoritmo pa,ra obtener las soluciones periódicas de un oscilador de Duffing con comportamiento caótico

Resultados del simulador SMART frente a señales sintéticas con modelo de orden reducido de BWR con ruido aditivo y multiplicativo

Muñoz-Cobo, J.; Montesino, M.; Peña Miralles, J.; Escrivá Castells, A.; Melara, J. (2011). Resultados del simulador SMART frente a señales sintéticas con modelo de orden reducido de BWR con ruido aditivo y multiplicativo. Nuclear España. (321):45-45. http://hdl.handle.net/10251/103740S454532

A criterion for the transition from wall to core peak gas volume fraction distributions in bubbly flows

[EN] It has been observed by many authors that for ascending bubbly flows, the gas fraction distributes radially in different manners. Depending on the flow conditions and channel characteristics, the bubbles may accumulate in the center of the pipe (core peak) or near the walls (wall peak). The radial distribution of gas fraction significantly affects the friction coefficient and the heat transfer. Therefore, it is important to be able to predict which distribution will appear under certain flow conditions. In this note, by analyzing a vast experimental data base, a criterion to identify the transition from core to wall peak is proposed. The transition occurs when both Reynolds and Weber numbers reach critical values (Rcrit = 1500, Wcrit = 8). This criterion is validated with our experimental results and with those found in the literature.Mendez Diaz, S.; Zenit, R.; Chiva Vicent, S.; Muñoz-Cobo, J.; Martinez-Martinez, S. (2012). A criterion for the transition from wall to core peak gas volume fraction distributions in bubbly flows. International Journal of Multiphase Flow. 43:56-61. doi:10.1016/j.ijmultiphaseflow.2012.02.012S56614