Experimental research on reverse flow phenomenon in an equal-height-difference natural circulation system at low pressure

Abstract

Due to the inherent safety feature and potential for improved economy, natural circulation systems have been extensively applied in energy and chemical industries, especially in the nuclear industry. Different from traditional natural circulation systems (TNCSs), an equal-height-difference natural circulation system (EHDNCS) consists of a heat source, a heat sink, upper horizontal pipe and lower horizontal pipe, where the height difference between its heat source and sink is zero. Besides, the heat sink is commonly the ocean when an EHDNCS is adopted in the floating nuclear power plant (FNPP). Nevertheless, the research on such natural circulation systems is not sufficient because of few potential applications in the past. The present work experimentally investigated the flow characteristics of an EHDNCS. The visualization experimental results indicated that the water in the heat sink could reversely flow into the upper horizontal pipe. Furthermore, the influence factors on the reverse flow behaviors, e.g., flow rate and temperature difference, were experimentally studied in detail. It was found that the reverse flow length could be well evaluated by the Richardson number Ri. Finally, an experimental correlation was obtained to predict the reverse flow length based on Richardson number Ri.