Droplet Dynamics in Vertical Gas-Liquid Annular Flow Data zyxwvutsrqp for the two-dimensional velocity and size of entrained drops carried by the gas core during upward annular gas liquid flow are presented. The measurements of velocity and size were made simulta- neously using a new experimental technique. Information on the varia- tion zyxwvutsrqp of the drop velocity with flow rates, radial position in the core, and drop size are presented and analyzed. Droplet velocity is shown to increase with size, counter to intuitive expectation. This is explained in terms of highly modified drag-Reynolds number relationships caused zyxwv by the high turbulence level in the core. Introduction zyxwvutsrqp During the simultaneous upward flow of gas and liquid in a vertical pipe a variety of flow patterns can exist. At high gas and low liquid flow rates an annular flow pattern is observed. Here part of the liquid flows upward along the wall as a thin, highly wavy film with the gas flowing in the core. The remainder of the liquid is carried by the gas phase in the form of drops. Condi- tions exist where a considerable fraction of the liquid feed is entrained, as shown by Ueda (1981). Zabaras et zyxwvutsrqp al. (1986), and others. The distribution of the liquid between the film and dis- persed phase and the process of interchange as drops deposit into the film and new drops are created by the gas flow can have pro- found effects on transfer phenomena. Attempts to model these processes ignoring the role of the drops can lead to considerable error, as recently shown with respect to momentum transfer (Lopes and Dukler, 1986). The prediction of rates of deposition and the motion of the drops relative to the gas phase requires an understanding of the dynamics of the drop motion. Experimental difficulties have resulted in few applicable studies in the literature. In order to obtain useful information it is necessary to simultaneously measure size and velocity of the individual drops in a fast-moving gas stream. Most earlier stud- ies analyzed photographic records obtained from high-speed flash, cine film, or video tape. The difficulty in locating and tracking individual drops and the tedium of frame study resulted in relative few measurements for each condition. There- fore the statistical reliability of the data was low. This method averages the information over the tube cross-sectional area and over at least a few diameters of axial length. As a result, extract- The prcscnt addrus of J. C. B. Lopes is Schlumberger-Doll Research, Ridgefield. CT 06877- 4108. J. C. B. Lopes, A. E. Dukler Department of Chemical Engineering University of Houston Houston, TX ing data for local values is not possible. In these photographic methods only one component of the velocity was reported. Laser velocimetry methods have also been used. Here there zy is a special problem of optically penetrating the annular film. In addition, this method depends on the existence of Mie scattering, which is suppressed for the large drops observed in annular flow. A summary of previously reported data can be found in Table 1, from which the very limited nature of this information can be discerned. In the present work simultaneous measurements were made of the size as well as the axial and radial components of the velocity vector along the radius in the gas core. This paper presents the velocity data and their dependence on flow condi- tions, radial position, and drop size. In an attempt to interpret the data, speculations are advanced for the nature of the interac- tions between the gas and drops in this highly turbulent gas core. Droplet Velocity Measurements Experimental technique The annual flow experiments were conducted in a 10 m long vertical Plexiglas cylindrical pipe of 50.74 zyx +. 0.18 mm ID. The fluids used were air and water, which were injected at the bot- tom of the column. Both temperature and pressure were moni- tored at the measuring location and experiments were run at superficial velocities in the ranges 14-25 m/s for the gas and 0.03-0.12 m/s for the liquid. The experimental measurements of droplet sizes and velocities were made at 8.9 m from the gas injection point, equivalent to a distance of 175 pipe diameters. The simultaneous measurement of droplet diameter and two droplet velocity components was obtained by use of an optical laser technique originally developed by Semiat and Dukler (1981). A comprehensive description of the method applied to AIChE Journal June 1987 Vol. 33, No. 6 1013