Movements and mechanical stresses in gas-filled flat plate solar collectors

Sealed gas filled flat plate solar collectors will have stresses in the material since volume and pressure varies in the gas when the temperature changes. Several geometries were analyzed and it could be seen that it is possible reducing the stresses and improve the safety factor of the weakest point in the construction by using larger area and/or reducing the distance between glass and absorber and/or change width and height relationship so the tubes are getting longer. Further it could be shown that the safety factor won't always get improved with reinforcements. It is so because when an already strong part of the collector gets reinforced it will expose weaker parts for higher stresses. The finite element method was used for finding out the stresses.

Design of gas filled solar collectors

With a suitable gas filling used between cover glass and absorber in a flat plate solar collector, it is possible achieving better thermal performance at the same time as the distance betweenabsorber and glass can be reduced. Though, even if there is no vacuum inside the box, there will be potential risks for exhaustion due to stresses depending on the gas volume varies as the temperature varies. This study found out that it is possible build such a collector with less material in the absorber and the tubes and still getting better performance, without risks for exhaustion.

Las relaciones entre Chile y Suecia durante el primer gobierno de Olof Palme, 1969-1976

Durante el primer gobierno del socialdemócrata Olof Palme, las relaciones bilaterales entre Chile y Suecia fueron las más intensas de toda su historia, tanto en cercanía como en conflictividad. La razón la encontramos en los distintos fenómenos políticos que vivió Chile en ese periodo, puesto que Palme coincidió temporalmente con tres gobiernos claramente diferenciados: la Democracia Cristiana, la Unidad Popular y el Régimen Militar. Si las relaciones sueco-chilenas tuvieron su mejor momento durante el mandato de Salvador Allende, el golpe de Estado significó todo lo contrario. El compromiso que tuvo el embajador de Suecia, Harald Edelstam, por quienes eran perseguidos en Chile le llevó a su expulsión, lo que se tradujo en un claro deterioro de las relaciones y el inicio de una nueva etapa marcada por el gran contingente de exiliados que comenzaron a llegar a Suecia. Este trabajo analiza los principales acontecimientos diplomáticos ocurridos entre Chile y Suecia así como las consecuencias que tuvieron durante el gobierno de Olof Palme.

Thermal losses in sealed, gas-filled flat plate solar collectors

A sealed space between absorber and cover glass makes it possible reducing the influence of humidity condensate and dust at the same time as the enclosed space can be filled with a suitable gas for lowering the losses. This paper is about the size of the losses in these collectors. A calculating model of a gas-filled flat plate solar collector was built in Matlab with standard heat transfer formulas. It showed that the total loss can be reduced up to 20% when changing to an inert gas. It is also possible using a much shorter distance and still achieve low losses at the same time as the mechanical stresses in the material is reduce.