Study On Thermal Performance Of Evacuated Tubular Solar Air Collector With Inserted Tubes

Compared with the solar collector using water as working fluid, solar air collector has some advantage such as antifreezing in winter, less effect of air leakage on the operating performance, anticorrosive, etc. So the solar air collector can be used for indoor heating, ventilation, solar powered drying and so on. Among the various types of air collector, nowadays flat plate solar air collectors are mature commercialized products. However, evacuated tubular solar air collector with inserted tubes is more promising due to its simple structure, low heat loss coefficient and high efficiency. In this paper experimental and theoretical studies have been conducted on the thermal performance of a novel evacuated tubular solar air collector with inserted tubes.Experimental study was carried out to analyze the dynamic and average thermal performance under different weather conditions. It was found that under different season conditions the efficiency is around 60%. The air collector can also achieve good performance at 0~90°under N-S orientation. The time constant of the assembled solar air collector and the single collector tube is 23min, 12min respectively which shows that it's more inert. A 3D-unsteady numerical model has been developed to study the evacuated tubular air collector with inserted metal tube. It takes into account variation of radiant boundary with the time and space for the evacuated tube absorber. So it can simulate the collector performance more accurately. This model is used to predict all-day performance of the evacuated tubular solar collector under varying radiant conditions and weather conditions. The thermal performance of evacuated tubular air collector with inserted tubes was analyzed experimentally and theoretically. Under typical Spring and Summer conditions the heat loss coefficient was 2~6 W/m2K when the collecting temperature varied at the range 30~80℃.The results of this paper indicate that evacuated tubular solar air collector with inserted tubes has low heat loss coefficient and high efficiency, so it's very promising in the application of indoor heating, ventilation, drying, etc.