Measurement of Liquid Film in Annular Flow Using X-Ray Densitometry

Abstract

Two-phase annular flow film thickness is a crucial parameter in nuclear thermal hydraulics, yet conventional measurement techniques such as impedance probes may compromise accuracy by directly contacting and potentially disturbing the flow. Non-intrusive measurement methods are needed to provide more reliable film thickness data for improved reactor safety calculations in Boiling Water Reactors (BWR), Pressurized Water Reactors (PWR), and accident scenarios such as Loss of Coolant Accidents (LOCA), where accurate film thickness data is essential for reliable predictions in reactor analysis codes. This thesis evaluates x-ray densitometry as a non-intrusive alternative that measures film thickness without flow disturbance. Film thickness measurements were obtained for two-phase annular flow in a 9.5 mm pipe across various superficial gas and liquid velocities and compared against impedance probe data and established correlations. Through a calibration procedure, a correction factor is determined to enhance the x-ray densitometry system's measurement accuracy for film thickness. Using a specially designed test facility available at RPI, comprehensive film thickness data across annular flow conditions is generated, while simultaneously capturing dynamic wave characteristics including wave height, velocity and frequency. The experimental results were benchmarked against RPI's parallel-wire impedance probe data and established film thickness correlations. Based on these comparisons, one film thickness correlation was refined to achieve better agreement with both the x-ray densitometry results and two supplementary experimental datasets.