Film thickness of free falling water flow on a large-scale ellipsoidal surface

Falling water film flow on large-scale curved dome of passive containment, of which the data is very scarce, plays a crucial role for the thermal-hydraulic behaviors of passive containment cooling system (PCCS) in advanced nuclear power plant. It exhibits a developing phenomenon in nature because of continuous changes of the inclined angle, the width and the extend angle of the flow channel in the longitudinal direction. In order to examine the influences of these continuously varying factors on the flow characteristics, the film thickness of free falling water flow on a large-scale ellipsoidal surface with continuously varying inclined angle and extend angle has been measured experimentally. The working fluid is the low hardness municipal water, of which the inlet temperature is the same as ambient environment. Capacitive non-contact displacement transducers, Micro-Epsilon capaNCDT-CS10 sensors, are used to measure the film thickness at different locations with inclined angle ranging from 18° to 76°. The range of the film Reynolds number is from 360 to 2175. Detailed analyses on the relationship between the dimensionless film thickness and the film Reynolds number at different longitudinal positions on the dome surface are carried out. No obvious influence on the evolution of falling film caused by the continuous changes of the inclined angle, the width and the extend angle of flow channel on the dome can be observed. A new empirical correlation of film thickness on the ellipsoid dome surface is suggested based on the data obtained in the present experiments. Most of experimental data points fall in the range of ±15% around its prediction. Comparisons are also made between the suggested correlation with other theoretical or empirical correlations of film thickness in straight channels reported in the literature, as well as the numerical results on curved surface by computational fluid dynamics software COMMIX and GASFLOW-MPI. Fairly good agreements are observed, proving that the suggested correlation can predict the film thickness on the curved dome surface of PCCS with much accuracy and then provide a more reliable basis for further analysis of the conjugate heat and mass transfer of PCCS.