Thermo-fluid dynamics of steam–water direct contact condensation in steam-filled inclined and vertical channels

The present study investigates the thermo-fluid dynamics of direct contact condensation when subcooled water is injected into inclined/vertical channels filled with saturated steam. This mode of direct contact condensation has not yet been extensively investigated although it is frequently encountered and the flow physics is significantly different. Observations from the present computational analysis indicate that countercurrent flow is established within the channel once water injection starts leading to onset of Kelvin–Helmholtz instability, irrespective of channel orientation. Rayleigh–Taylor instability plays an increasingly dominant role as the channel inclination increases toward the vertical. The combined effect of these hydrodynamic instabilities, along with simultaneous interfacial heat transfer and steam condensation, destabilizes the steam–water interface causing transition between various flow regimes. These transitions are identified with respect to water injection velocity (1−5 m/s), injection diameter (dD=0.25−0.75), temperature of the injected water (293−431.98 K) and channel inclination (0°–90°). The flow regimes in a vertical channel are observed to be significantly different from that in inclined channels. Regime transitions in vertical channels are further observed to be dependent on various parameters studied. Depending on the flow regimes and their transitions, it is observed that channel blockage—partially or completely—may take place and steam pockets may be formed within the channel under different conditions. The analysis establishes that hydrodynamic effects have a greater impact—as compared to thermal effects—on steam–water interface dynamics in this mode of direct contact condensation.