The hydrodynamics of an individual transient slug in a voided line

The hydrodynamics of an individual transient liquid slug in a voided line was investigated both analytically and experimentally. In the experiment, liquid slugs of various lengths were propelled into an initially empty, horizontal, clear PVC pipe under several different air driving pressures. The pipe reach terminated in an open-ended elbow; pressure-time histories created by the slugs impacting on the elbow were recorded. In order to better understand the complexities of the slug motion, high-speed movies were taken to visualize the flow prior to slug impact at the elbow.; The recorded peak pressures at the elbow were correlated with the initial slug length and the initial driving pressure. Short slugs produced variable flow characteristics and random-like pressure peaks at the elbow, whereas medium and long slugs were more repeatable. In particular, the medium and long slugs retained more of their initial mass than did the short slugs before reaching the elbow. They also displayed two distinct pressure peaks when impacting at the elbow.; The flow visualization revealed that the front end of the slugs remained nearly planar during the motion. The short slugs were influenced more by air entrainment since they travelled a longer relative distance in the pipe and accelerated at a higher rate than the longer slugs; the onset of Taylor instability was observed, but complete disintegration did not take place. The medium and long slugs were divided into two distinct masses separated by a misty region; this flow pattern corresponded with the double pressure peaks recorded at the elbow. In these slugs, the second mass phase was followed by a long length of stratified two-phase flow.; An analytical model was developed to predict the slug dynamics: it accounted for loss of liquid mass of the slug as well as transient flow of the driving gas in the pipe behind the accelerating slug. Momentum transfer at the elbow was based on an incompressible liquid mass with no air entrainment. Reasonable estimates of the peak pressures at the elbow were obtained, as well as the resulting impulse loads caused by the slug impact. The comparison of these estimates to those of a similar study revealed somewhat similar trends.; The numerical results were presented as a set of scaled dimensionless curves; they were used to predict slug motion in a hypothetical system found in power plants. Limitations in the use of those curves when analyzing prototype piping were addressed.