A new criterion for the identification of the bubble slug transition in vertical tubes

Vertical two-phase flow is normally classified into the four basic flow reg imes bubble, slug, churn and annular flow The transition between the differ ent flow regimes does not occur suddenly and many extensions of this classi fication can be found in literature. For the prediction of flow patterns em pirical and theoretical flow pattern maps have been developed. A new criter ion is presented for the transition between bubble and slug flow which is b ased on local instantaneous conductivity measurements with a wire mesh sens or (1 kHz that means 1024 frames per second, 242 measuring points in a tube cross section area). The high resolution allows the calculation of particl e size distributions The transition from homogeneous bubble flow to heterog eneous bubble flow is indicated by the appearance of a bimodal bubble size distribution. If the equivalent bubble diameter exceeds the tube diameter t he transition from bubble to slug flow occurs. A comparison of the new crit erion with different empirical and theoretical flow maps shows a good agree ment.