Evaluation Methods for Heat Pipes in Solar Thermal Collectors – Test Equipment and First Results
Abstract
Heat pipes in non- or low-concentrating vacuum tube collectors offer by the decoupling of absorber and solar circuit as compared to direct-flow collectors the advantage of a simpler hydraulic interconnection, while reducing heat loads in case of stagnation. However, it should be noted that heat pipes can only transfer a certain amount of thermal power and that the system of heat pipe and heat exchanger (manifold) represents an additional thermal resistance in the useful heat path of a solar collector. In a current research project1 at the Institut für Solarenergieforschung Hameln (ISFH) the heat transfer characteristics of heat pipes applied in solar collectors are investigated. By experimental examination of heat pipes and manifolds with the aid of model calculations potentials for optimization in existing solutions are worked out. The focus of this paper comprises the presentation of newly developed test rigs and experimental results of the thermal behavior of commercially available heat pipes and manifolds in solar thermal collectors.