Flat-plate Solar Natural Circulation Thermal Properties Of The Hot Water System

Solar power hot water system is the most mature technique and the most challenging green energy technique in the field of solar power utilization nowadays. For the reason of simple construction, low cost and good applicability, the flat-plate thermosyphon solar hot water system appeals many people's eyes. In order to make the flat-plate thermosyphon solar hot water system be better,to improve the utilization efficiency of solar power, many experts and learners studied this technology deeply, which maked the theories on the flat-plate thermosyphon solar hot water system become more sophisticated.Nowadays, there're many theories and studies on the flat-plate thermosyphon solar hot water system, but theories on temperature distribution of the whole water system is few. For this reason, this paper planned to establish a physical and mathematical model on the flat-plate thermosyphon solar hot water system. then with the numerical method to solve the differential equation, this paper used the language 'Visual Basic' to workout the program of the instantaneous temperature distribution of the whole circulation system; Furthermore, theories nowadays are mostly on the research of the dayl, while very few at night. Based on this question, with the model established, this paper discussed the flow field without solar radiation.Via experiment, this paper maked an experimental research on the flat plate thermosyphon solar hot water system. It measured one day's instantaneous mass flow rate and instantaneous efficiency, and instantaneous temperature distribution in the collector and the tank in the day and night. After that, it maked the experimental results into curves and compared with the theoretical results. Via comparison, it found that the curves of experimental results and the curves of theoretical results inosculated very well, errors between them were not big,Which proved that the model established is correct.At last, this paper analysed the influence of the system's construction to the heat performance. The results showed:1. The height change doesn't affect the system's daylight efficiency, so when design a solar water system, we must lower the height as much as possible on the precondition of reasonable disposition, in order to work easily, which meet the principle of economic and safety.2. This paper analysed the influence of the height between the collector and the tank to the heat performance at night. The datus showed that at night, in order to decrease the heat loss, used the hot water in the tank fully, we must let the bottom of the tank higher than the top of the collector, for decreasing the counter-flow rate.3. This paper analysed the influence of the height between the top of the upper circulation pipe and the bottom of the tank to the daylight's heat performance. The results showed that the farther the distance was, the higher the efficiency was; The closer the distance between the top of the upper pipe and the bottom of the tank was, the lower the system's efficiency was.4. At the same collector's inlet temperature and the same environment temperature, with the increase of the solar radiation, the heat loss of the collector increased. The smaller the inclined angle of the plate was, the more the heat loss of the whole system was. The bigger the inclined angle of the plate was, the more the heat loss of the whole system was.Via the research of this paper, we get the theoretical gist for the flat-plate thermosyphon solar hot water system design, and provided a direction for the real engineering application.