ArticleThe absorption of radiation in solar stills
Abstract
A method of calculating the fraction of incident solar radiation which is productively used in solar stills is presented. The number of variables which can influence this make it necessary to standarize on set values of glass thickness and extinction coefficent and liner reflectance. The variables considered are the day of the year, latitude, cover slope, orientation, percentage diffuse radiation and insolation intermittency. The complexity of the resulting functions, together with the number of varibles, makes it difficult to accurately predict what the still mean effective absorptance will be for a given set of conditions. It is found that insolation intermittency has an insignificant effect and that the greater the daily proportion of diffuse radiation, the lower the absorptance. Using the equations presented, a mean effective absorptance can be calculated for any given combination of the variables.
Résumé
On présente une méthode de calcul de la fraction de rayonnement solaire incident qui s'utilise de manière productive dans les appareils de distillation solaire. Le grand nombre de paramètres variables dont il convient de tenir compte le rend néssaire d'établir des valeurs normalisées pour l'épaisseur du verre ainsi que le coefficient d'extinction et de réflexion du revêtement de l'appareil. Les paramètres variables que l'on considère sont le jour de l'an, la latitude, la pente de couverture, l'orientation, le pourcentage de rayonnement diffus et la nature intermittente de l'insolation. La nature complexe des fonctions résultantes, ainsi que le grand nombre de paramètres variables le rend difficule de prévoir de manière précise l'absorption moyenne effective de l'appareil selon les conditions de fonctionnement. On établit que la nature intermittente de l'insolation a un effet peu important et que plus la proportion journalière de rayonnement diffus est grande, plus l'absorption est faible. En utilisant les équations présentées, on est en mesure de calculer une absorption moyenne effective pour toute combinaison donnée de paramètres variables.
Resumen
Se presenta un método para calcular la fracción de radiación solar incidente que se utiliza en régimen productivo en los destiladores solares. Debido al número de variables que pueden influir en ello, es necesario establecer valores fijos de espesor de vidrio, coeficiente de extinción y reflectancia del revestimiento. Las variables consideradas son el día del año, latitud, pendiente de la cubierta, orientación, porcentaje de radiación difusa e intermitencia de insolación. La complejidad de las funciones resultantes, unido al número de variables, hace difícil pronosticar con certeza cuál será la absortancia efectiva media del destilador frente a una serie de condiciones dadas. Se ha encontrado que la intermitencia de insolación ejerce un efecto insignificante y que, cuanto mayor sea la proporción diaria de radiación difusa, menos será la absortancia. Usando las ecuaciones presentadas, se puede calcular una absortancia efectiva media para cualquier combinación concreta de las variables.
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Digital simulation of transient solar still processes
Solar Energy
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Diathermous materials and properties of surfaces
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