Publication: Análisis y optimización del diseño de los tubos de un receptor solar de torre central
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2019-07
Defense date
2019-07-05
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Abstract
Los receptores son el elemento más crítico de las torres termosolares debido a las
condiciones de trabajo extremas a las que están expuestos. Estas condiciones suelen
producir roturas en los tubos que forman cada uno de los paneles del receptor, llevando a
paradas indeseadas de la central y a unas pérdidas económicas que reducen la
confiabilidad y la eficiencia de estas plantas.
En la actualidad, la geometría de los receptores no se ha optimizado todavía y continúan
produciéndose fallos en los tubos, por eso en este trabajo se ha realizado un estudio de
los parámetros característicos de geometría y de funcionamiento de un receptor externo
cilíndrico, así como de los problemas que suelen surgir en estos, para conocer la
influencia que tiene la variación de dichos parámetros en el funcionamiento de la central
y cómo podrían optimizarse.
En este proyecto se ha propuesto una nueva solución que consiste en aumentar la
separación entre tubos del receptor para que llegue un mayor flujo de calor a la parte
trasera y así conseguir aumentar la temperatura de trabajo del receptor. De esta forma se
consigue reducir el gradiente de temperaturas entre la superficie externa y la superficie
interna del tubo, causa principal de la generación de tensiones térmicas. Por tanto, se ha
realizado un estudio de las separaciones tanto entre tubos como con la pared que se
encuentra en la zona posterior de estos para optimizar la geometría, además de pruebas
con diferentes condiciones de contorno como distintos fluidos de trabajo o diferentes
materiales de los tubos. También se ha estudiado la influencia del flujo de radiación
incidente en el receptor, de la temperatura media de trabajo y del flujo másico de fluido
que circula por el receptor. Además, se ha realizado un pequeño estudio de la influencia
del viento en el comportamiento de estos receptores.
Las simulaciones de los diferentes casos se han realizado con el software Ansys Fluent
19.1 y el análisis posterior se ha realizado mediante el software MATLAB para conseguir
unos resultados más precisos.
Se ha estudiado la temperatura en las superficies interna y externa de un tubo
representativo y se ha obtenido que la separación entre tubos tiene una influencia muy
notable en el comportamiento del receptor, mientras que la separación trasera apenas
influye en los resultados. Además, se ha observado un buen comportamiento utilizando metales fundidos como fluido de trabajo, dado que refrigeran mejor la superficie de los
tubos y permiten aumentar la temperatura de trabajo. Para permitir aumentar esta
temperatura, se ha llegado a la conclusión de que el material más adecuado para los tubos
es el Incoloy 800H, además de obtenerse muy buenos resultados utilizando este material.
Solar receivers are the most critical element of the solar power towers due to the extreme conditions that they are exposed. These conditions usually produce ruptures in the tubes that form each of the panels of the receiver, leading to unwanted stops and economic losses that reduce the reliability and the efficiency of these plants. Currently, the geometry of these receivers has not been optimized yet and failures continue to occur in the tubes. For this reason, in this work a study of the characteristic parameters of geometry and operation of a cylindrical external receiver has been carried out, as well as the problems that usually arise in these to know the influence of these parameters on the operation of the plant and how they could be optimized. In this project, a new solution has been proposed that consists in increasing the separation between receiver tubes so that a greater heat flow reaches the rear and thus achieves an increase in the working temperature of the receiver. In this way, it is possible to reduce the temperature gradient between the external surface and the internal surface of the tube, the main cause of generation of thermal stresses. Therefore, a study of the separations between tubes and with the wall at the back of the tubes has been carried out to optimize the geometry, in addition to tests with different boundary conditions as different working fluids or tube materials. The influence of the incident radiation flow on the receiver, the average working temperature and the mass flow has also been studied. In addition, a small study of the influence of wind on the behavior of these receptors has been carried out. The simulations of these cases have been carried out with the software Ansys Fluent 19.1 and post-processed with the software MATLAB to obtain more precise results. The temperature on the surfaces of a representative tube has been studied and it has been obtained that the separation between tubes has a very remarkable influence on the behavior of the receiver, while the rear separation hardly influences the results. In addition, good behavior has been obtained using molten metals as working fluid, because they cool the surface of the tubes and allow to increase the working temperature. To allow to increase this temperature, it has been concluded that the most suitable material for the tubes is the Incoloy 800H, in addition to obtaining very good results using this material.
Solar receivers are the most critical element of the solar power towers due to the extreme conditions that they are exposed. These conditions usually produce ruptures in the tubes that form each of the panels of the receiver, leading to unwanted stops and economic losses that reduce the reliability and the efficiency of these plants. Currently, the geometry of these receivers has not been optimized yet and failures continue to occur in the tubes. For this reason, in this work a study of the characteristic parameters of geometry and operation of a cylindrical external receiver has been carried out, as well as the problems that usually arise in these to know the influence of these parameters on the operation of the plant and how they could be optimized. In this project, a new solution has been proposed that consists in increasing the separation between receiver tubes so that a greater heat flow reaches the rear and thus achieves an increase in the working temperature of the receiver. In this way, it is possible to reduce the temperature gradient between the external surface and the internal surface of the tube, the main cause of generation of thermal stresses. Therefore, a study of the separations between tubes and with the wall at the back of the tubes has been carried out to optimize the geometry, in addition to tests with different boundary conditions as different working fluids or tube materials. The influence of the incident radiation flow on the receiver, the average working temperature and the mass flow has also been studied. In addition, a small study of the influence of wind on the behavior of these receptors has been carried out. The simulations of these cases have been carried out with the software Ansys Fluent 19.1 and post-processed with the software MATLAB to obtain more precise results. The temperature on the surfaces of a representative tube has been studied and it has been obtained that the separation between tubes has a very remarkable influence on the behavior of the receiver, while the rear separation hardly influences the results. In addition, good behavior has been obtained using molten metals as working fluid, because they cool the surface of the tubes and allow to increase the working temperature. To allow to increase this temperature, it has been concluded that the most suitable material for the tubes is the Incoloy 800H, in addition to obtaining very good results using this material.
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Keywords
Energías renovables, Energía solar, Torre solar, Centros termosolares de torre, Receptor central, Fluido caloportador, Simulación CFD, Tensiones térmicas