抄録
Research and development of renewable energy is very important. Because solar energy has a large amount of energy, it is attracted many attentions. In this paper, solar water heater using supercritical carbon dioxide as working fluid is proposed and studied. For supercritical carbon dioxide, a small change in temperature or pressure can result in a large change in density, especially in the state close to the critical point. Thus, natural convective flow of the supercritical carbon dioxide can be easily induced by solar heating or water cooling. Flow property and heat transfer of supercritical CO_2 natural convection are important for this system. This study the flow and heat transfer behavior of supercritical CO_2natural circulation system on a closed natural circulation loop (NCL) model. The fluid temperature in the loop varies between 298.15 K and 1023 K, which is across the CO_2 critical temperature. The diameter of NCL is 6 mm and 15 mm. The results show that the flow of diameter of 15 mm is proved to be always single direction stable flow. NLC with diameter of 15 mm have a higher heat efficiency than that with diameter of 6 mm.
