A prototype liquid film sensor for high-temperature steam-water experiments has been developed. The sensor shape simulates a boiling water reactor (BWR) fuel rod. The pulse-echo method can be utilized to measure the thickness of the liquid film covering the sensor surface. A piezoelectric element is soldered onto the inside of the sensor casing which consists of two curved casing pieces. After the piezoelectric element is attached, the two casing pieces are laser welded together. It is confirmed that the temperature rise at the time of the laser welding does not influence soldering of the piezoelectric element. The pressure proof test shows that the sensor can be used at a high-pressure condition of 7 MPa. Simple air-water experiments are done at atmospheric pressure to confirm the liquid film thickness can be measured with the sensor. The fluctuation of the liquid film thickness is satisfactorily captured with the sensor. The minimum and maximum thicknesses are 0.084 and 0.180 mm, respectively. The amplitude of the waveform at 286• C is predicted by the calculation based on the acoustic impedance. It is expected that the sensor is able to measure the liquid film thickness even at BWR operating conditions.
A plasma-induced bi-polar arc and its plasma response were studied in a tokamak configuration, and a drastic change in the plasma potential near the arcing metal rod was found. Cylindrically concentric equi-potential surfaces are formed around the cathode spot, and a small change in the plasma potential observed at the plasma-wall interface breaks an ambipolarity there, forming a current channel across the toroidal plasma between the cathode spot and the vacuum chamber.
Air-water experiments were performed for the BvVR steam dryer in order to elucidate droplet removal characteristics of the vane. Based on the results, a simplified vane was developed and its droplet removal characteristics were confirmed by air-water experiments using a whole dryer model.Phase-Doppler anemometer was used to measure droplet diameter distributions. In the experiments of the current vane with four-wave stages and 120° bend angle, almost all of the droplets were found to be trapped in the first and second vane stages. For the air velocity of 3.1 m/s, 90% of the inlet droplets were trapped there and 4% were trapped in the third and fourth stages, resulting in 6% being carried over. Sauter mean diameters at the exit were 6 and 5 µm while at the inlet they were 71 and 64 µ.m for the respective air velocities of 1and3111/s. Based on the \Veber number evaluation, the possible mechanism for the fine droplet generation was considered to be the breakup of droplets due to impingement on the liquid film formed in the vane surface.From the above results, the simplified vane with two-wave stages was developed. In order to remove fine droplets, the bend angle of the vane was reduced to 90°, in which a larger inertia force is exerted on finer droplets generated by breakup. Experiments for the whole dryer model showed that the developed vane could achieve the same droplet removal characteristics as the current vane without increasing the pressure drop of the dryer. A design having ten dryer bank rows and 1.2 m height, which is 0.8 m shorter than the current dryer, is possible for the dryer using the new simplified vane.
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