Preliminary test of an ultrasonic liquid film sensor for high-temperature steam–water two-phase flow experiments

Abstract

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.

Application results of a prototype ultrasonic liquid film sensor to a 7 MPa steam–water two-phase flow experiment

“…It is necessary to process the acquired waveforms for the calculation of the liquid film thickness [5]. A reference waveform r(t) as the reflection at the sensor surface was needed to separate the pulse reflected at the liquid film surface from the observed waveforms o(t).…”

“…The amplitude of the difference waveform at 288 • C was smaller than that at the room temperature. This result was estimated by the calculation based on the acoustic impedance [5]. However, the maximum of crosscorrelation φ2 kmax reached almost 0.9.…”

“…The subtraction results d1 k (t) were called the difference waveforms [5]. Next, the cross-correlations φ k were calculated between the mean waveformō(t) and each Figure 5.…”

“…The piezoelectric element received some pulses reflected at the sensor surface and the liquid film surface. To find the accurate time difference between the two pulses, waveform subtraction was utilized [5]. It was evaluated that the liquid film thickness of 0.03 mm could be measured by the ultrasonic frequency of 5 MHz [4].…”

“…Recently, a prototype ultrasonic liquid film sensor for high-temperature steam−water experiments has been developed by the authors [5]. The applicability of the sensor to the steam−water environment was 2 G. Aoyama et al confirmed at 190 • C [6].…”