An investigation into the conditional stability of direct contact steam condensation is presented. Direct contact steam condensation systems heat process fluids more effectively than indirect contact heat exchangers because the total energy of the steam is introduced directly into the process fluid, bypassing any resistances associated with having to cross the heat exchanger boundary. In the present work, superheated steam is injected perpendicular to a flow of subcooled liquid water. Conditional stability of direct contact steam condensation stems from the type of fluctuations exhibited by the steam plume structure. Under certain flow conditions the steam plume condenses in the form of a stable conical jet with little to no acoustic noise or resultant pressure fluctuations. However, other conditions cause the steam plume to increase in oscillation intensity, eventually transitioning to an intermittent bubbling structure that results in high-amplitude acoustic noise and large pressure fluctuations in the flow of liquid water. A regime map is presented to establish the process criteria for the onset of instability of condensation. The transitional profile to instability is also presented as an analysis of plume oscillation frequencies and associated pressure oscillations propagating from these fluctuations. It is found that, as the mode of condensation goes unstable, steam plume oscillations increase in intensity and decrease in frequency until the structure collapses into bubbles that provoke strong pressure oscillations in the surrounding water.
The stability of a steam plume during direct-contact condensation is investigated into a crossflow of subcooled water with mass fluxes that are higher (>600 kg/m2s) and a nozzle diameter (2.4 mm) that is smaller than typically seen in the literature. The transition from a stable steam plume to an unstable plume associated with the formation and collapse of steam bubbles is characterized by high-speed imaging and high-frequency pressure measurements. Four regimes are observed: stable, condensation oscillation, transition, and unstable. A regime map and spectral signatures of the different flow regimes are provided. Results are compared with correlations from the literature, which are typically derived for lower mass fluxes, larger nozzles, and injection into stagnant pools of water.
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