Publication: Caracterización, diseño y construcción del colector de un secadero solar en Nicaragua
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2011-06-30
Defense date
2011-06
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Abstract
El secado de productos agrícolas es de gran importancia en países en vías de desarrollo. La mayoría de estos países se ubican en la zona tropical del planeta, donde la humedad ambiente es muy alta y los productos precisan de secado para su procesado. El uso de secaderos solares se está extendiendo mucho en estas regiones por su independencia del suministro eléctrico, que no siempre está garantizado, además de porque en estas regiones, por su localización geográfica, existe alta disponibilidad de energía solar. La Universidad Carlos III de Madrid y la Universidad Nacional de Nicaragua UNAN – FAREM de Estelí han estado trabajando en conjunto en el desarrollo de este tipo de instalaciones. En concreto, la instalación de la que disponen trata de un secadero solar de tipo pasivo (esto es, su única fuente de energía es el sol) destinado a secar madera. El secadero consta de un colector solar que recibe radiación y transmite calor en forma de convección natural al aire contenido en su interior, haciendo que fluya al interior de la cámara de secado ubicada aguas abajo de la corriente. Al aumentar la temperatura del aire su punto de saturación aumentará, admitiendo más vapor de agua. Dicho vapor provendrá del albergado en la madera, que con el aumento de temperatura aumentará su presión de vapor igualándola con la del ambiente y se evaporará. El presente trabajo se centrará en el colector solar de este tipo de instalaciones. Se estudiará el comportamiento de la corriente en el colector de ambas instalaciones con el objetivo de caracterizarlas, compararlas y crear un diseño que optimice los valores de los parámetros de la corriente según lo requiera el proceso de secado. Con ese fin se creará además un modelo matemático teórico que estudia el comportamiento fluidotermodinámico de la corriente en el colector en función del clima, la posición geográfica y la geometría del colector, entre otros. El modelo se basa en un balance energético en el colector, y haciendo uso de las ecuaciones de transferencia de calor permite conocer los parámetros de la corriente a la salida del colector en función de los datos mencionados. Dicho modelo se programará en MathCad, permitiendo así el cambio en los valores de los mencionados factores para ver su influencia en los resultados. Gracias a las medidas experimentales se respaldará dicho modelo y se probará que sus resultados son razonables, pudiendo hacer uso de él para buscar el diseño óptimo del nuevo colector. Tras decidir el diseño óptimo del nuevo colector se procede a su construcción, para posteriormente caracterizarlo con medidas experimentales y comprobar si se obtienen los resultados esperados. ______________________________________________________________________________________________________________
The drying of agricultural products is of great importance to developing countries. Most of these countries are located in tropical areas in environments where humidity is very high and products need to be dried for processing. The use of solar dryers is growing quickly in these regions due to its independence from electric supply which is not always available, besides the ease to find solar energy in those locations on the Earth. The University Carlos III de Madrid and the National University of Nicaragua UNAN- FAREM of Estelí have been working together to develop these types of installations. Specifically, the installations that they have established are passive solar dryers (i.e. their only source of energy is the sun) with the purpose of drying wood. The dryer has a solar collector that receives radiation and transmits heat by means convection into the air contained in the unit, forcing it to flow into the drying chamber located downstream. By increasing the temperature of the air, the point of saturation increases as well, allowing more steam to be absorbed from the wood. As the temperature increases the partial pressures of the water contained in the wood matches that of the air causing evaporation. The work being developed will be focused on the solar collector of these types of dryers. This research will examine the behaviour of the stream inside each of solar collectors for both universities in the aim of observing their performance, comparing them, and creating a design to optimize the parameters of the stream for the requirement of drying process. With this target a theoretical mathematical model will be created to check the fluidthermodynamic behaviour as a function of climate, location, and geometry of the collector. The model is based on an energetic balance in the collector, and using equations of heat transfer gives as output the parameters of the air at the end of the collector as a function of the mentioned input data. This model will be programmed in MathCad which allows changes in input data to check its influence in the results. The experimental measures will back up this model proving that the results are logical. This model can be used to find optimal design of the new collector Once a design has been chosen the collector can be built. The parameters can be measured to check if they match the theoretical expected results.
The drying of agricultural products is of great importance to developing countries. Most of these countries are located in tropical areas in environments where humidity is very high and products need to be dried for processing. The use of solar dryers is growing quickly in these regions due to its independence from electric supply which is not always available, besides the ease to find solar energy in those locations on the Earth. The University Carlos III de Madrid and the National University of Nicaragua UNAN- FAREM of Estelí have been working together to develop these types of installations. Specifically, the installations that they have established are passive solar dryers (i.e. their only source of energy is the sun) with the purpose of drying wood. The dryer has a solar collector that receives radiation and transmits heat by means convection into the air contained in the unit, forcing it to flow into the drying chamber located downstream. By increasing the temperature of the air, the point of saturation increases as well, allowing more steam to be absorbed from the wood. As the temperature increases the partial pressures of the water contained in the wood matches that of the air causing evaporation. The work being developed will be focused on the solar collector of these types of dryers. This research will examine the behaviour of the stream inside each of solar collectors for both universities in the aim of observing their performance, comparing them, and creating a design to optimize the parameters of the stream for the requirement of drying process. With this target a theoretical mathematical model will be created to check the fluidthermodynamic behaviour as a function of climate, location, and geometry of the collector. The model is based on an energetic balance in the collector, and using equations of heat transfer gives as output the parameters of the air at the end of the collector as a function of the mentioned input data. This model will be programmed in MathCad which allows changes in input data to check its influence in the results. The experimental measures will back up this model proving that the results are logical. This model can be used to find optimal design of the new collector Once a design has been chosen the collector can be built. The parameters can be measured to check if they match the theoretical expected results.
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Keywords
Energía solar, Colectores solares, Países en vías de desarrollo, Transferencia de calor