DEVELOPMENT OF DIGITAL IMAGE-ANALYSIS TECHNIQUES FOR THE STUDY OF VELOCITY AND VOID PROFILES IN SLUG FLOW

This paper describes the development of a nonintrusive flow visualizat ion method for the quantitative study of the dynamic velocity and void profiles across the pipe cross section in slug how. The method utiliz es novel digital image analysis and computer graphics techniques. Slug how in a 75 mm diameter, 10 m long Plexiglass pipe is recorded on vid eo using super-VHS cameras and an audio-visual mixer. Sixty images are obtained every second and these are digitized and analyzed on a SGI g raphics workstation. Detailed information regarding the local velocity and void distribution is obtained from the analysis and is used to ge nerate velocity and void profiles across the pipe at different distanc es into the slug. Results show that gas is released into the slug in t he form of pulses of bubbles resulting in the existence of large, frot hy, highly aerated structures in the mixing zone. The hydrodynamic bou ndary layer is destroyed at the slug front but begins to redevelop in the mixing zone. It becomes fully developed at the end of the mixing z one and the one-seventh power law profile for velocity profile is appl icable. At the end of the mixing zone, the gas moves towards the top o f the pipe and the Void fraction distribution tends to a steady profil e. A process dynamic model is developed to predict the variation of th e average liquid holdup within the slug. (C) 1997 Elsevier Science Ltd .