Experimental investigation of pressure pulsation during direct contact condensation of steam with noncondensable gas in a square minichannel

Pressure pulsation is a characteristic dynamic response of steam direct contact condensation (DCC) in confined channels and is strongly influenced by noncondensable gas and inlet operating conditions. Steam-air DCC in a square minichannel was investigated experimentally using selected 1.0 s post-stabilization pressure segments. The effects of noncondensable gas content, subcooled-water mass flux, steam mass flux, and subcooled-water temperature were characterized using time-domain pressure signals, root-mean-square pressure fluctuation, paired extreme-pressure statistics, power spectral density analysis, energy-selected Hankel SVD reconstruction, and reconstructed pressure-state trajectories. For each operating condition, the minimum Hankel rank required to reach at least 80% cumulative squared-singular-value energy was retained. Increasing the noncondensable gas content from 0% to 3% reduced the root-mean-square pressure fluctuation from 7.86 to 1.99 kPa, decreased the within-record mean ± SD of the minimum-event depth from 27.67 ± 12.53 to 7.82 ± 1.54 kPa, and contracted the reconstructed pressure-state area from 151.52 to 9.19 kPa 2 . Increasing the subcooled-water mass flux from 298.263 to 597.516 kg·m −2 ·s −1 increased the root-mean-square pressure fluctuation from 2.86 to 7.59 kPa. Higher steam mass flux and higher subcooled-water temperature also attenuated the pressure response, whereas increasing subcooled-water mass flux strengthened it. The opposing liquid- and vapor-side mass-flux effects were consistently resolved across amplitude, event-scale, spectral, and reconstructed pressure-state descriptors. The energy-selected Hankel framework further provided a common basis for comparing reconstructed trajectory geometry among operating conditions, extending the pressure-pulsation characterization beyond conventional amplitude metrics.