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http://hdl.handle.net/10261/130
20150827T23:11:28Z

CFD simulation of a reversible solid oxide microtubular cell
http://hdl.handle.net/10261/107901
Título : CFD simulation of a reversible solid oxide microtubular cell
Autor : GarcíaCamprubí, M.; LagunaBercero, M. A.; Fueyo, Norberto
Resumen: In this work, the authors introduce a comprehensive model and the corresponding 3D numerical tool for the simulation of reversible microtubular solid oxide fuel cells. It is based on a previous inhouse model for SOFC [1], to which some new features has been added to extend its applicability to SOEC. The model considers the following physical phenomena: (i) fluid flow through channels and porous media; (ii) multicomponent mass transfer within channels and electrodes; (iii) heat transfer due to conduction, convection and radiation; (iv) charge motion; and (v) electrochemical reaction. The numerical algorithm to solve this mathematical model is implemented in OpenFOAM, an open source CFD toolbox based on the finitevolume method.
Descripción : Trabajo presentado al 10th European SOFC Forum celebrado en Lucerna (Suiza) del 26 al 29 de Junio de 2012.
20141121T10:21:49Z

Transient twodimensional simulation of real flood events in a mediterranean floodplain
http://hdl.handle.net/10261/100618
Título : Transient twodimensional simulation of real flood events in a mediterranean floodplain
Autor : GonzálezSanchis, María; Murillo, J.; Latorre, B.; Comín, Francisco A.; GarcíaNavarro, P.
Resumen: The application of a twodimensional (2D) finite volume numerical model to real flood events in the Ebro River is presented. The hydraulic model used is based on the 2D transient shallowwater equations on the irregular bed that are able to compute flow advance over a dry bed. This study involves the reliable simulation of not only the flood wave advance but also the drying process in a series of events of different magnitude. The importance of the correct characterization of the roughness coefficient and the topography is emphasized in the study. The former is estimated from a previous classification of structurally homogeneous habitats, and the latter is defined by merging the digital terrain model data with a hydraulic river bed elevation reconstruction algorithm. The calibration of the full model resulting from the roughness, bed river, and flow simulation models is based on field measurements of the flooded area for two steady discharges. The validation is performed by comparing the numerical results with the water levels measured during five flood events at certain times, with the flooded area and time series of continuous point measurements of water depth during different situations throughout the year. Because the model provides correct predictions of the surface processes both for low and high flow discharges, the simulation results are used to analyze the present floodplain hydrodynamics. In the same way, different topographic scenarios, on the basis of changes in the hydraulic riverfloodplain connectivity, are generated to analyze their potentially beneficial effect in the floodplain geomorphic dynamics. © 2012 American Society of Civil Engineers.
20140731T11:37:40Z

Dynamic modeling of a thermal system for a hightemperature PEM fuel cell
http://hdl.handle.net/10261/97453
Título : Dynamic modeling of a thermal system for a hightemperature PEM fuel cell
Autor : Roda, V.; Puleston, Pablo Federico; Barreras Toledo, Félix; Moré, J. J.
Resumen: Hightemperature PEM fuel cells (HTPEMFCs) operation differs from that of conventional ones, because the working temperature has to be controlled between 120°C and 180°C. The proton conducting membrane that functions as electrolyte is made of a PBI polymer doped with phosphoric acid and is highly hygroscopic. On the one hand, if its working temperature decreases below 120°C it absorbs water and the acid is pushed out, reducing the overall proton conductivity. On the other, if t he device is forced to work at temperatures above 180°C, the evaporation of phosphoric acid is accelerated, and the stack lifetime can be dramatically shortened. Therefore, the control system must incorporate specific operational strategies, different to the ones used in lowtemperature PEMFCs. In such framework, the objective of this research is to provide a dynamic model of the thermal subsystem of a HTPEMFC, aiming to develop a proficient temperature controller for a small stack manufactured at LIFTEC. As a first stage, the set of fullorder differential equation is obtained assuming concentrate parameters and following a heat flow balance approach. Next, resorting to physical consideration, it is worked into a reducedorder statespace model, suitable for control design pur poses. Moreover, taking advantage of electrical analogies, a modular equivalent circuit is proposed for the thermal model of each cell. Lumping such modules allows to straightforwardly obtain, not only the whole dynamic model of the stack under consideration, but also of a large stack that will be tackled in a future stage of this project. In particular, the thermal dynamic model presented in this work corresponds to a device comprising five MEAs Celtec® P1100W manufactured by BASF Fuel Cells, with an active area of 605cm2. The bipolar plates are machined in aluminum, and coated with a thin ceramic layer of CrN of 2.5μm thick to prevent corrosion, but preserving a high electric conductivity. As independent thermal actuators, the stack incorporates flexible electrical resistance wires surrounding each MEA in every ndividual cell. It is also equipped with electrical resistance cartridges placed in the main gas collectors. Thus, by increasing the temperature of the reactant gases, they are able to transfer heat to the bipolar plates and the MEAs, providing a more uni form and rapid heating of the whole stack. In addition, the fuel cell has been thermally insulated, in order to reduce the heating power demand and to benefit of the heat generated by the stack. In this way, at certain operation conditions, the reaction thermal energy could be large enough to keep the temperature within the range recommended by the MEAs’ manufacturer. However, when the stack operates at high current densities, the excess heat must be extracted, in order to maintain the temperature of the stack in the working range. To this end, the insulation device has a ventilation system equipped with axial fans. Note that the heat extracted can be utilize in heating systems if the HTPEMFC stack is used as a combined heat and power unit (CHP).
20140530T10:04:52Z

Placa de pila de combustible con geometría de flujo en forma de "espina de pez"
http://hdl.handle.net/10261/94594
Título : Placa de pila de combustible con geometría de flujo en forma de "espina de pez"
Autor : Lincheta Mesa, Eduardo; Barreras Toledo, Félix; Lozano Fantoba, Antonio; Valiño García, Luis; Mustata Oroviceanu, Radu
Resumen: La placa de pila de combustible, que se utiliza generalmente para distribuir de forma homogénea los fluidos reactantes sobre las áreas de reacción química correspondientes a las capas catalíticas (electrodos), presenta en cada una de estas áreas de reacción química una geometría de flujo en forma de "espina de pez" que comprende canales delimitados por unos nervios, dispuestos de tal forma que el canal de entrada se bifurca en canales que ocupan dos estructuras laberínticas simétricas y que terminan confluyendo en un canal de salida, de manera que se optimizan las reacciones electroquímicas responsables de la generación de electricidad y adicionalmente, se facilita la salida a los productos de las reacciones.
20140401T08:26:09Z