Investigation on Pressure Oscillations Frequency for High Pressure Gas Double-hole Jet

Abstract

For boiling water reactors and small reactors, an effective way to reduce containment pressure is to discharge gas from the containment into the suppression pool. Based on the above background, a series of experiments were conducted to investigate the pressure oscillations frequency of steam-air gas discharged into a supercooled water pool. The air mass fraction was 0.0-0.4, and the hole pitch was 1.5d-3d. The air compressor and electric boiler generated air and steam, respectively. The steam and air were mixed and discharged into the supercooled water pool. A high-frequency dynamic pressure sensor was used at the nozzle outlet to record the pressure oscillation signal, and a high-speed camera captures jet plume images. The fast Fourier transform (FFT) was used to process the pressure signal, and the peak value of the frequency domain signal is the dominant frequency of the oscillation. The image observation reveals that in the case of a double-hole jet, the interference of the two gas plumes causes the gas plumes to converge or even agglomerate to form a combined jet. The dominant frequency of the double-hole jet is lower than that of the single-hole jet because of the increase in the dimension of the double-hole jet plume, which leads to a longer condensation time. Therefore, increasing the number of holes will result in a decrease in the dominant frequency of the oscillation, which may be closer to the equipment's natural frequency and lead to resonance damage. For temperature effects, the condensation time of the plume is shorter as the subcooling increases, so the oscillation frequency increases with subcooling. For the effect of hole pitch, the dominant frequency increases with hole pitch. The water temperature between the two gas plumes decreases as the hole pitch increases, and the gas plumes condense faster and take less time to condense. Based on the research conclusions of the dominant frequency characteristics of the steam jet condensation, an empirical equation for predicting the dominant frequency was proposed, and the predicted deviation is within the range of -15%-20%. The oscillation dominant frequency of the steam-air mixture jet increases with the subcooling degree and the hole pitch, which is consistent with the conclusion of the steam jet. When steam-air mixture gas jets, the dominant frequency is inversely proportional to the non-condensable gas mass fraction. The reason is that during the steam-air mixture gas jets, the concentration of non-condensable gas increases after steam condensation between the gas-water interfaces, which inhibits the mass transfer process, resulting in a longer condensation time. As the fraction of non-condensable gases increases, the mass transfer inhibition becomes more pronounced.

Keywords

• mixture gas
• double-hole jet
• pressure oscillation
• dominant frequency