Statistical characterization of liquid film fluctuations during gas-liquid two-phase counter-current flow in a 1/30 scaled-down test facility of a pressurized water reactor (PWR) hot leg.

• The experiment was conducted during the liquid–gas counter-current two-phase flow in a 1/30 scaled-down of PWR hot leg. • The liquid thickening on the upper edge of the hydraulic jump triggers the liquid blockage to initiate the CCFL. • The statistical characterizations were investigated on the basis of both the locus and the flow parameters. • The time-domain and frequency-domain analyses implies a good agreement with the visual observations, while the wavelet analysis is able to differ the obtained flow regimes. The present work investigates the statistical characteristics of the fluctuations of the liquid film thickness obtained by resistive-conductance probe signals of a complex geometry representing a 1/30 down-scaled of a PWR hot leg. Here, four locations at the horizontal part of the test section were assessed, while the flow development was investigated through a close observation by using a high-speed video camera. Next, the normalized voltages, indicating the liquid film thickness fluctuations, are shown in the time-series. From the fluctuations, the amplitudes representing the film thickness were recorded. Hence, such statistical diagnostic tools were applied on the basis of time-domain, frequency-domain and also time–frequency domain analyses. From the probability density function, the distributions of the fluctuations were assessed, whereas the power spectral density function describes the dominant frequencies. In addition, the Kolmogorov entropy denotes the chaotic level of the signal, meanwhile the wavelet energy corresponds to several details on the wavy interfaces on the basis of its frequency scales. Next, those parameters were statistically employed to elaborate the interfacial behaviors due to the signal characteristics. The results indicate that the low dominant frequency corresponds to the occurrence of either liquid blockage or slugs during the acquisition, meanwhile the largest scale fluctuations reveal the wave movements. [ABSTRACT FROM AUTHOR]