Artículos de investigación PDI
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- ItemInfluence of crystal structure on the thermophysical properties and figures-of-merit of propylene glycol: water-based SiC nanofluids(Powder Technology, 2024) Vallejo, Javier P.; Febrero-Garrido, Lara; Cacabelos, Antón; González-Gil, Arturo; Lugo, LuisSilicon carbide is a material with a promising thermal conductivity. However, no literature has been found on SiC nanofluids based on propylene glycol:water mixtures (widely used in renewable installations). Likewise, the contribution of α-SiC and β-SiC to the thermophysical properties of nanofluids has scarcely been explored. In this work, dispersions of α-SiC and β-SiC on propylene glycol:water 30:70 wt% at 1 and 2% wt% concentration are designed. Densities, thermal conductivities, dynamic viscosities, and isobaric heat capacities from 293.15 to 313.15 K are obtained by vibrating tube densimetry, transient-hot-wire technique, rotational rheometry and differential scanning calorimetry, respectively. Convective heat transfer performance is also assessed using figures-of-merit. Thermal conductivity and viscosity show a greater dependence on the crystal structure. The β-SiC nanofluids present the highest increases of thermal conductivity (12%) and dynamic viscosity (17%). The least complex crystal structure (β-SiC) exhibits better prospects for convection applications both for laminar and turbulent flow.
- ItemDevelopment of an improved dynamic model of a Stirling engine and a performance analysis of a cogeneration plant(Applied Thermal Engineering, 2014-08-13) Cacabelos, Antón; Eguía, Pablo; Míguez, José Luis; Rey, Guillermo; Arce, ElenaIn this paper, the authors develop a dynamic model of a commercial micro-combined heat and power (mCHP) unit and analyse its dynamic behaviour when the engine is running at different mass flow inputs. The simulation predicts with a low root mean bias error (RMSE) the most important outputs from the cogeneration unit during the starting, steady-state and stopping periods. Furthermore, the presentedc transient model reproduces the behaviour of the cogeneration unit when the fuel and air mass flows are changing. The obtained results are discussed, and the different possibilities for the variation of the thermal to power ratio are analysed. These combinations include the variation of the flow distribution inside the machine and the position of the exhaust heat exchanger. The power to thermal ratio can be modified between 0.15 and 0.26 for these combinations. The performance of the engine and the variation of the heat source temperature are also analysed theoretically. The simulation results conclude that an important saving could be obtained when the electrical to thermal ratio (ETTR) is tracked for the power or thermal demands from a dwelling.
- ItemStudy of natural zeolites for hydrogen purification: CO2 adsorption capacity and kinetic mechanism(Fuel, 2024-11-15) Maceiras, Rocío; Falcón, Pablo; Alfonsín, Víctor; Pérez-Rial, Leticia; Feijoo, JorgeHydrogen is considered a promising alternative fuel. However, in order to be used, it is necessary to achieve a high degree of purity through purification processes. Adsorption is considered one of the most important techniques for purification. In this research, the CO2 adsorption capacity and kinetic mechanism of natural zeolite were investigated with the aim to understand the carbon dioxide adsorption behaviour under different operating conditions. Multicomponent breakthrough curves of a mixture of H2/CO/CH4/CO2 were obtained at different pressures and gas flow rates. Moreover, the analysis of CO2 adsorption equilibrium and kinetics were carried out. The obtained adsorption isotherm data were fitted with different model equations. Freundlich, Sips and Toth models showed the best fit for the experimental data, indicating the heterogeneous nature of the adsorbent surfaces. The carbon dioxide adsorption kinetic was analysed using different kinetic models, obtaining that the adsorption process is both physical and chemical and that the limiting step of the diffusion process is intraparticle diffusion, although other processes are also involved such as diffusion through the boundary layer.
- ItemSistema multiestático para la suplantación (spoofing) de señales GPS(X Congreso Nacional de I+D en Defensa y Seguridad (DESEi+d 2023), 2023) Núñez-Ortuño, José M.; González-Coma, José P.; Nocelo López, Rubén; Troncoso-Pastoriza, Francisco; Álvarez-Hernández, MaríaActualmente, los sistemas y plataformas que emplean nuestras Fuerzas Armada, tienen gran dependencia de datos procedentes de fuentes GNSS (Global Navigation Satellite System). En un ataque tradicional de suplantación (spoofing) de señales de sistemas GNSS, la emisión de las señales suele realizarse desde un mismo punto, radiando una señal que resulta ser el agregado de las señales que emitirían los satélites suplantados de la constelación original en la ZOI (Zona de Interés). Este tipo de ataque resulta fácilmente detectable en el emplazamiento de la víctima mediante el empleo de técnicas de DOA (Direction of Arrival) por cualquier equipo de guerra electrónica moderno o una antena CRPA (Controlled Reception Pattern Antenna). Una de las técnicas que complican la detección en este tipo de escenario es la de realizar un ataque simultáneo desde varias ubicaciones (ataque multiestático). El demostrador que se presenta en este trabajo, permite realizar este tipo de ataque que, ejecutado desde varios nodos atacantes de manera sincronizada, complica la detección de un ataque de GNSS Spoofing.
- ItemSistema de perturbación (spoofing) para receptores GPS embarcados(XI Congreso Nacional de I+D en Defensa y Seguridad (DESEi+d 2024), 2024) Núñez-Ortuño, José M.; Troncoso-Pastoriza, FranciscoLas pruebas de perturbación y suplantación de señal GNSS realizadas por el CUD-ENM en buques de la Armada y aeronaves del Ejército del Aire han revelado vulnerabilidades en estos sistemas, afectando tanto a equipos de navegación como a otros sistemas no previstos. El CUD-ENM ha desarrollado LOKI, un sistema capaz de realizar ataques de jamming y spoofing en múltiples bandas y constelaciones, suplantando posición y tiempo GPS con precisión. Esta herramienta permite evaluar y catalogar la resiliencia de los equipos receptores GPS y sistemas dependientes a bordo de los buques de la Armada. El sistema LOKI ha participado en las maniobras NEMO-22, MARSEC-22/23/24 y MINEX-23/24, creando ambientes GNSS degradados en los que se han realizado ataques efectivos sobre más de 15 unidades navales y aeronaves propias y de la coalición. En esta comunicación se describe la arquitectura software y hardware del sistema desarrollado, así como sus principales características.