Experimental analysis on a novel solar collector system achieved by supercritical CO₂ natural convection

Solar collector has become a hot topic both in scientific research and engineering applications. Among the various applications, the hot water supply demand accounts for a large part of social energy consumption and has become one promising field. The present study deals with a novel solar thermal conversion and water heater system achieved by supercritical CO₂ natural circulation. Experimental systems are established and tested in Zhejiang Province (around N 30.0, E 120.6) of southeast China. The current system is designed to operate in the supercritical region, thus the system can be compactly made and achieve smooth high rate natural convective flow. During the tests, supercritical CO₂ pipe flow with Reynolds number higher than 6700 is found. The CO₂ fluid temperature in the heat exchanger can be as high as 80 C and a stable supply of hot water above 45 C is achieved. In the seasonal tests, relative high collector efficiency generally above 60.0% is obtained. Thermal and performance analysis is carried out with the experiment data. Comparisons between the present system and previous solar water heaters are also made in this paper.