Thesis SIMULACIÓN COMPUTACIONAL DE LA TRANSFERENCIA DE CALOR RADIATIVA EN UN MEDIO DISPERSIVO APLICADO A LAGUNAS SOLARES
Date
2018
Authors
MUÑOZ FLORES, FELIPE LEONARDO
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Abstract
Las lagunas solares son sistemas de almacenamiento de energía térmica de grandes dimensiones,capaces de suplir la demanda de diversos procesos industriales en el ámbito de la energíasolar (tales como desalinización, calefacción, refrigeración, generación de potencia a baja temperatura,tratamiento de materiales, secado industrial, etc).La simplicidad constructiva de las lagunas solares, los bajos costos de operación, su capacidadde entregar grandes cantidades de energía por largos períodos de tiempo, y un muy bajo impactoambiental, hacen de las lagunas solares una alternativa interesante de estudio. La laguna solaractúa básicamente como un colector térmico a gran escala, capaz de almacenar la energía dela radiación solar durante el día y mantener el sistema a altas temperaturas de forma estable ypor largos periodos de tiempo, incluso durante la noche, donde las pérdidas de calor hacia elmedio exterior son disminuidas. La laguna solar se construye a través de la estabilización de ungradiente de sales en un medio acuoso, formándose así tres zonas características: una zona superficialcon una muy baja concentración de sales (UCZ, del inglés “Upper Convective Zone”),la cual está expuesta hacia el medio exterior, una zona de almacenamiento térmico saturadade sales (LCZ, “Low Convective Zone”), y una zona intermedia con un gradiente de salinidad(NCZ, “Non Convective Zone”), en la cual la convección natural es suprimida debido a unaestratificación estable de la densidad, inhibiendo las pérdidas de calor por convección desde lazona de almacenamiento hacia el medio exterior de la laguna. Los trabajos en torno a lagunassolares han abordado diversos aspectos de los fenómenos físicos involucrados, y se han aplicadodiversas metodologías en su estudio. Sin embargo, en ninguna de estas investigaciones seha hecho un estudio del comportamiento del campo de radiación térmica al interior del medioparticipante (emisor, absorbedor y dispersor de la energía radiativa).El presente trabajo estudia el comportamiento térmico de lagunas solares, generando unmodelo computacional en estado transiente que resuelve numéricamente la ecuación de intercambioradiativo. El modelo computacional obtiene el campo de intensidad radiativa por mediodel Método de las ordenadas discretas, y éste es acoplado a la ecuación de balance global deenergía (la cual incluye a los demás métodos de conducción y convección de calor) y es resueltapor medio del método de volúmenes finitos). Se asume en el modelo una completa estabilizacióndel gradiente de salinidad y del campo de flujos (variables impuestas).Los resultados obtenidos muestran que el modelo logra recrear el comportamiento térmicode la laguna solar en el largo plazo, evidenciando una alta temperatura en la zona de almacenamientorespecto al resto de la laguna, con leves descensos estacionales. Una vez comprobada laefectividad del modelo se realizan 3 tipos de estudios. Influencia de las propiedades radiativasdel medio participante. Estudio del comportamiento de la laguna solar para diferentes espesoresde las zonas características. Y la operación de la laguna solar bajo diferentes niveles de radiación solar (pruebas de operación en distintas localidades).
The Solar Ponds are large-scale thermal energy storage systems, capable of supplying thedemand of several industrial processes in the solar energy field (such as desalination, heating,cooling, power generation at low temperature, treatment of materials, industrial drying, etc.)The constructive simplicity of the solar ponds, the low operating costs, their capacity to generatelarge amounts of energy for long periods of time, and a very low environmental impact,make solar ponds an interesting alternative for study. Basically, solar pond acts as a large-scalethermal collector, capable of storing the energy of solar radiation during the day and to maintainthe system, at high temperatures, stable for long periods of time, even at night, where heat lossestoward the external environment are reduced. The solar pond is built through the stabilizationof a salt gradient in an aqueous medium, thus forming three characteristic zones: a surface areawith a very low concentration of salts (Upper Convective Zone, UCZ), which is exposed to theexternal environment, a thermal storage zone saturated with salts (Low Convective Zone, LCZ)and an intermediate zone with a salinity gradient (Non Convective Zone, NCZ), in which naturalconvection is suppressed due to a stable stratification of the density, inhibiting heat losses byconvection from the storage area towards the external environment of the pond. Previous worksrelated to solar ponds has addressed various aspects of the physical phenomena involved, andhence several methodologies have been applied in the researches. However, in none of these investigationsa study has been made to analyze the behavior of the thermal radiation field insidethe participating medium (emitter, absorber and scattering of radiative energy).The present work studies the thermal behavior of solar ponds, generating a computationalmodel in transient state that solves numerically the radiative exchange equation. The computational model obtains the field of radiative intensity by Discrete Ordinate Method, and this iscoupled to the global energy balance equation (which includes the other methods of conductionand heat convection) and it is solved through the Finite Volume Method. A complete stabilizationof the salinity gradient and the velocity field (imposed variables) is assumed in the model.The results obtained show that the model manages to recreate the thermal behavior of thesolar pond in the long term, evidencing a high temperature in the storage area compared to therest of the pond, with slight seasonal declines. Once the effectiveness of the model is verified,3 types of studies are carried out: the Influence of the radiative properties of the participatingmedium, a study of the behavior of the solar pond for different thicknesses of the characteristiczones, and the operation of the solar pond under different levels of solar radiation (tests ofoperation in different locations).
The Solar Ponds are large-scale thermal energy storage systems, capable of supplying thedemand of several industrial processes in the solar energy field (such as desalination, heating,cooling, power generation at low temperature, treatment of materials, industrial drying, etc.)The constructive simplicity of the solar ponds, the low operating costs, their capacity to generatelarge amounts of energy for long periods of time, and a very low environmental impact,make solar ponds an interesting alternative for study. Basically, solar pond acts as a large-scalethermal collector, capable of storing the energy of solar radiation during the day and to maintainthe system, at high temperatures, stable for long periods of time, even at night, where heat lossestoward the external environment are reduced. The solar pond is built through the stabilizationof a salt gradient in an aqueous medium, thus forming three characteristic zones: a surface areawith a very low concentration of salts (Upper Convective Zone, UCZ), which is exposed to theexternal environment, a thermal storage zone saturated with salts (Low Convective Zone, LCZ)and an intermediate zone with a salinity gradient (Non Convective Zone, NCZ), in which naturalconvection is suppressed due to a stable stratification of the density, inhibiting heat losses byconvection from the storage area towards the external environment of the pond. Previous worksrelated to solar ponds has addressed various aspects of the physical phenomena involved, andhence several methodologies have been applied in the researches. However, in none of these investigationsa study has been made to analyze the behavior of the thermal radiation field insidethe participating medium (emitter, absorber and scattering of radiative energy).The present work studies the thermal behavior of solar ponds, generating a computationalmodel in transient state that solves numerically the radiative exchange equation. The computational model obtains the field of radiative intensity by Discrete Ordinate Method, and this iscoupled to the global energy balance equation (which includes the other methods of conductionand heat convection) and it is solved through the Finite Volume Method. A complete stabilizationof the salinity gradient and the velocity field (imposed variables) is assumed in the model.The results obtained show that the model manages to recreate the thermal behavior of thesolar pond in the long term, evidencing a high temperature in the storage area compared to therest of the pond, with slight seasonal declines. Once the effectiveness of the model is verified,3 types of studies are carried out: the Influence of the radiative properties of the participatingmedium, a study of the behavior of the solar pond for different thicknesses of the characteristiczones, and the operation of the solar pond under different levels of solar radiation (tests ofoperation in different locations).
Description
Catalogado desde la version PDF de la tesis.
Keywords
ENERGIA SOLAR , LAGUNAS SOLARES , METODO DE LAS ORDENADAS DISCRETAS , SIMULACION COMPUTACIONAL
