Modeling of Liquid Sprays and Thermal Mixing in Desuperheating Applications

Computational modeling is performed for liquid sprays and thermal mixing in desuperheating applications, in which water sprays are injected into a high-temperature steam crossflow (H₂O^l-H₂O^g system) to reduce the enthalpy. The basis of the model is the standard RANS approach coupled to the Lagrangian treatment for statistical groups (parcels) representing the physical droplet population. A vaporization/boiling model is developed for the treatment of phase change under a single chemical species environment. Additionally, the best performing hybrid breakup models depicting the hydrodynamic breakup process governed by the Kelvin-Helmholtz and Rayleigh-Taylor instabilities, are used. The calculations are run for both air-H₂O^l and H₂O^l-H₂O^g systems. Under crossflow conditions, the calculations show that liquid sprays undergo sudden atomization near the injector tip, and have a much smaller characteristic droplet size compared to sprays injected into quiescent environments. This is attributed to the larger gas-droplet relative velocities drastically enhancing the Weber number. Additionally, a blockage effect of the spray on the crossflow is observed in the near-nozzle field, and the typical entrainment of small droplets into the wake is captured in the predictions. The region of maximum cooling coincides with the generation of the highest values of interfacial area produced by the sudden atomization in the near field.