Dynamics of chugging phenomenon induced by subsonic and supersonic steam–air jet condensation in water flow

Chugging, a typical unstable flow pattern caused by steam-water direct contact condensation, should be paid more attention in engineering applications due to its accompanying low-frequency and high amplitude pressure pulse. In this paper, it was experimentally found that both subsonic and supersonic steam–air jet condensation could trigger chugging in a confined channel. As for such conditions, the chugging-caused pressure pulses all had two dominant frequencies with different amplitudes, and the one with larger amplitude was mainly distributed in the low-frequency zone of 15–45 Hz and 30–50 Hz. The brilliant image of steam-water phase interface captured by a high-speed camera showed that the mechanism of chugging was the sharp and low-frequency stretching and shrinking of the phase interface because of the periodic aggregation and dissipation of air layer. The subsonic steam–air jet condensation could trigger chugging only with a small amount of air, which therefore should be prevented as far as possible in engineering. However, for supersonic steam–air jet condensation, chugging could be triggered as soon as the air mass fraction reached a critical value because the incoming flow had severely damage effect on the air layer. By considering the steam mass flux, condensation driven potential, water Reynolds number and air mass fraction, the correlations of dominant frequency of chugging for subsonic and supersonic steam–air jet condensation were given, with deviations in the range of ± 20% and 15%, respectively.