気泡流からスラグ流への遷移

Abstract

Although many flow pattern maps for upward flow of gas-liquid mixtures in vertical pipes have been proposed, there is poor agreement among these maps. Part of the reason is that most of the flow pattern maps are based on visual observation and therefore involve the subjectivity of the observer. Another important reason for the bubble-slug transition of the flow pattern map is that the flow may not have been fully developed at the position of observation because the entrance region for the slug flow is large and dependent on the method of air injection.In this work, in order to investigate the effects of pipe diameter and air injector on the transition from bubble to slug flow, the experiments were carried out in three transparent acrylic plastic pipes of 20.3mm, 29.8mm and 39.6mm diameters and air was injected through various different injectors which were drilled radially in walls. And in order to distinguish flow patterns objectively the void properties were measured with electrical resistivity probe technique at the axial positions of 150 diameters, 137 diameters and 101 diameters from the air injectors for the test pipes of 20.3mm, 29.8mm and 39.6mm diameters respectively.The results are as follows. The characteristics of void fraction profile and bubble transit length distributions correspond to the flow patterns. The bubble-slug transition is influenced by the number of holes of air injectors rather than the diameter of holes of air injectors, and when the number of holes is increased slug flow pattern occures at higher flow rates of air. It seems that the formation of gas slug does not occure easily in a smaller diameter pipe. The limit of the transition boundary between bubble flow pattern and slug flow pattern is predicted by Eq.(8) with C0=1.1 and Egt=0.30.