Critical heat flux characteristics of flow boiling on a heater rod under inclined and conditions

Offshore floating nuclear power plants have been developed to supply power to remote regions. Since they are operated in an ocean environment, the thermal-hydraulic phenomena in the reactor core may be different from those in the land-based reactors. However, the experimental study on critical heat flux (CHF) under ocean condition is limited and its mechanism is unclear. In this study, an experiment was performed to measure CHF in a single heater rod under inclined and rolling conditions. To create the required environment to simulate the conditions of inclination and rolling, a rolling platform was designed and constructed. It could provide an inclination of up to 45 degrees and rolling of up to 45 degrees with a minimum period of 6 s. In the CHF test loop, the experimental conditions were set up to correspond to pressurized water reactor conditions, using the fluid-to-fluid scaling method. The working fluid used was R134a. The test section was a concentric annular channel composed of a heater rod and an unheated tube housing. The result of the inclination experiment suggested that in the most cases, the CHF was enhanced when compared with the vertical condition. In a limited number of cases of low-pressure and high-flow conditions, the CHF was degraded as compared to the vertical condition. These variations were proportional to the inclination angle and inversely proportional to the mass flux. From the results of the rolling experiment, a precursor of CHF was observed with a large fluctuation in temperature before the CHF, and its trigger was related to the CHF value of the inclined case. Based on this observation, the overall relations between the vertical, inclined, and rolling CHF values were derived. It was concluded that the rolling motion weakened the CHF enhancement and degradation effects of the inclination. (c) 2022 Elsevier Ltd. All rights reserved.