Experimental study on the direct contact condensation of steam jet in the passive safety injection tank

ABSTRACT The direct contact condensation and subsequent thermal mixing by the injected steam jet onto a quiescent coolant inside a tank were examined experimentally to simulate the phenomena in passive safety injection systems. Specifically, the influence of the steam injection velocity was studied. Even though the total flow rate of injected steam was unchanged, the pressure inside the tank increased quickly at the larger nozzle diameter. Additionally, at a larger nozzle diameter, the thickness of the thermal mixing zone decreased because the amount of direct contact condensation decreased. For the in-depth study on the role of the nozzle size for the thermal mixing, the particle image velocimetry method was used to understand the flow field of water inside the tank. The visualization results demonstrated the formation of a flow field in the coolant due to the expansion and contraction of the steam–air mixture boundary. Furthermore, the thermal mixing zone was found to be closely related to the penetration depth. Finally, a variety of penetration models were examined and compared against the experimental observation. The correlations based on the steam condensation approach under-predicted the penetration depth, whereas the approach that considers the momentum of non-condensable gas gave the reasonable prediction capability.