Research on condensation oscillation characteristic of steam submerged unstable jet condensation

The condensation oscillation characteristic of steam submerged jet condensation under unstable jet is studied experimentally. With high speed camera, the dynamic processes of steam bubbles are observed. Except for the bubble growth stage, bubble necking stage, bubble separation stage, the separated bubble oscillation and bubble collapse stages are captured. Moreover, dynamic pressure signals of condensation oscillation are measured and analyzed with methods of Probability Density Function (PDF) and Fast Fourier transform (FFT). When steam mass flux and water temperature is low, periodical dynamic pressure pulses appear obviously, which differ from the dynamic pressure signals under stable jet condensation. Under unstable jet, the peak of probability density of dynamic pressure signal located at negative axis, and slope trend at right side of peak is gentler than that at left side. However, under stable jet, the probability density distribution of dynamic pressure signal is similar to feature of Gaussian probability distribution. When water temperature is high, the periodical dynamic pressure pulses become indistinct. When dynamic pressure wave is dealt with FFT, multi-frequencies appear in the frequency spectrum. The first dominant frequency value is well corresponding to the growing and separating frequency of steam bubble. It is also the same to emerging frequency of periodical dynamic pressure pulses. Finally, the oscillation power spectrum is obtained. Oscillation power axial distribution of first dominant frequency band appears a peak near nozzle exit. And oscillation power distribution well matches the theoretical prediction distribution characteristic of monopole source oscillation.