The droplets entrained by the wet steam working medium of nuclear power plant pose a threat to the economy and safety of nuclear power plant. The humidity of steam is directly related to the working efficiency of nuclear power plant. In this paper, the ultrasonic attenuation coefficient in single-phase saturated steam is calculated. Based on the simplified ECAH model in the long wave region, the ultrasonic attenuation coefficient at different frequencies and the relationship between droplet size and humidity in the steam system of nuclear power plant are numerically simulated. For the relationship between droplet size, ultrasonic frequency, steam humidity and ultrasonic energy attenuation coefficient, the results are calculated and analyzed. Results and conclusion: through numerical simulation, the influence of hysteresis attenuation coefficient on the total ultrasonic attenuation coefficient in single-phase saturated steam medium can reach 90%. In single-phase steam medium, the fluctuation of temperature and pressure has little influence on the ultrasonic attenuation coefficient, while the deviation of ultrasonic frequency will have a large error on the ultrasonic attenuation coefficient in steam. The ultrasonic attenuation method is feasible for on-line measurement of steam humidity in nuclear power plant. Compared with the steam environment under other working conditions of nuclear power plant, the ultrasonic attenuation method is more suitable for the measurement of wet steam humidity under the conditions of humidity less than 9% and droplet size greater than 4μm.
The blocked accident of plate fuel assembly is one of the serious accidents in the reactor. It will worsen the heat transfer capacity of the coolant and even affect the safe operation of the reactor. Therefore, Particle Image Velocimetry (PIV) technology and the Laser Induced Fluorescence (LIF) technology are used in current paper to investigate the edge blockage accidents in a narrow rectangular channel with a continuous-wave laser and two high-speed cameras. During the experiments, the obstacle has great effect on the flow field and temperature field. It is found that large-scale vortex structure will be generated in the wake downstream of the obstacle. And where the vortices exist, the fluid temperature is also higher, which means that the vortices prevent the heat from escaping in time. Besides, the temperature distribution at different Re numbers is also analyzed. It can provide a validation for numerical simulations.
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