FULLY DEVELOPED GAS-LIQUID FLOWS.

The prediction of how phases distribute in a flow field is of first order importance in developing a scientific approach to multiphase flow. This involves the specification of the type of pattern and a quantitative description of where the phases are located for a given pattern. A striking feature of the physics is that macroscopic behavior is governed by small-scale interactions. A first step is to identify the critical microphysics by careful scientific (rather than empirical) analyses of results from studies in long pipelines. The "fully-developed" flows, that evolve far enough downstream, offer a simple system to test physical understanding. Furthermore, such studies provide results that can find direct use. Striking examples of the influence of small scale behavior in multiphase systems are the sensitivity of the flow pattern in a gas-solid fluidized bed to the characteristics of the solid particles and the influence of polymers on the behavior of a gas-liquid flow. An annular flow pattern changes to a stratified pattern because polymers destroy disturbance waves on the wall film (Al-Sarkhi and Hanratty, 2001a, 2001b). This eliminates atomization and reduces the ability of the film to climb up the wall against gravity. Polymers have also been observed to delay the transition to slug flow by decreasing the stability of slugs (Soleimani et al., 2002). The shedding of liquid from a slug can be related to the velocity of the gas bubble behind it. Polymers cause an increase in the velocity of this bubble by damping turbulence and, thereby, changing the flow pattern in the slug and the bubble velocity. This paper illustrates the approach outlined above by considering gas-liquid flows in horizontal or near-horizontal pipes. Stratified, slug and annular configurations are considered. The following recommendations are made: (1) An understanding of the physics governing the transition from one regime to another should be a top priority. (2) Critical issues in annular... [ABSTRACT FROM AUTHOR]