VOID FRACTION MEASUREMENTS USING NEUTRON RADIOGRAPHY

Real-time neutron radiography is being evaluated for studying the dyna mic behavior of two-phase flow and for measuring void fraction in vert ical and inclined water ducts. This technique provides a unique means of visualizing the behavior of fluid flow inside thick metal enclosure s. An air- wafer flow system was constructed to simulate vapor conditi ons encountered in a fluid flow duct. Air was injected into the bottom of the duct at flow rates up to 0.47 l/s (1 ft(3)/min). The waterflow rate was varied between 0 and 3.78 l/min (0 to 1 gal/min). The experi ments were performed at the Pennsylvania State University nuclear reac tor facility using a real-time neutron radiography camera. With a ther mal neutron flux on the order of 10(6) n/cm(2) . s(-1) directed throug h the thin duct dimension, the dynamic behavior of the air bubbles was clearly visible through 5-cm (2-in.)-thick aluminum support plates pl aced on both sides of the duct wall. Image analysis techniques were em ployed to extract void fractions from the data, which were recorded on videotape. This consisted of time averaging 256 video frames and meas uring the gray level distribution throughout the region. The distribut ion of the measured void fraction across the duct was determined for v arious air-water mixtures. Details of the results of experiments for a variety of air and waterflow conditions are presented.