Elimination of Thermal Bridges in the Construction of a Flat Low-Pressure Solar Collector by Means of a Vacuum Thermal Insulation Bushing

The paper deals with the elimination of heat losses in a flat low-pressure solar collector caused by direct contact of outlet pipefitting and the Al–Mg collector box. This is manifested by reduced thermal efficiency of the solar collector, especially in cold season, which is in direct conflict with its application, i.e., high-temperature application and application in cold conditions. The solution lies in the proposed new structural element—the vacuum thermal insulation bushing, which is able to simultaneously provide vacuum tightness of the collector box and interrupt the existing thermal conductive connection. The design philosophy was to transfer the vacuum insulating function component from the original pipe—collector box connection to the thermally insulated place bushing—collector box. Two prototypes were constructed and built into experimental vacuum chamber. Significant increase in the temperature gradient was found in performed experiments. Thermal insulation function, vacuum tightness, and resistance to thermomechanical stress have been demonstrated. The thermal insulation function has also been described through the simulations on a computational model, using finite volume method. The proposed solution of bushing has also successfully become the subject of patent protection.