Experimental blowdown results for initially isothermal, saturated water from a small pressure vessel containing internal geometry are presented. This experiment simulated a break in a large duct of approximately three diameters in length which exited from the vessel. Choking only occurred at the exit of the discharge duct, and the instantaneous internal vessel pressure distribution was nearly uniform. Most of the fluid within the vessel immediately after the initiation of the blowdown became superheated liquid. This thermodynamic state together with the activated wall cavities inside the vessel maintained a nearly constant internal vessel pressure history early in the blowdown. However, in the latter stage of the depressurization, the remaining fluid within the vessel was essentially in thermodynamic equilibrium. A nonuniform distribution of fluid quality within the vessel was also detected in this experiment. In addition, this experiment illustrates that transient, two-phase, critical flow in large diameter ducts is similar to steady, two-phase, critical flow in small diameter ducts.

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