A one-dimensional model able to predict the film distribution around the pipe wall under conditions typical of wet gas flow in near-horizontal pipes is presented. The model is based on the assumption that i) liquid droplets can only be entrained by the gas from the thick liquid layer flowing at pipe bottom and ii) the deposition of smaller droplets is related to an eddy diffusivity mechanism, while larger droplets deposit by gravitational settling mainly on the pipe bottom. The presence of a thin liquid film all around the pipe wall significantly affects the pressure gradient along the pipe. The present model is a new component of MAST (Multiphase flow Analysis and Simulation of Transitions), a transient, 1-D flow simulator developed for advanced flow assurance studies.
Pipeline transportation over long distances of natural gas in presence of a liquid phase is a common practice in the oil industry and can be extremely challenging when major flow assurance issues, such as corrosion or solid formation and deposition on pipe wall, arise. In these applications, at appreciable gas velocity, only part of the liquid flows at the pipe wall, while the gas entrains the remaining liquid in the form of droplets that tend to deposit back onto the wall layer. In a large diameter pipe, the resulting flow pattern is usually classified as stratified-dispersed (SD) flow. In this flow pattern, the critical parameter to be predicted is the flow rate and thickness distribution of the liquid layer flowing at pipe wall. This is because the split of the liquid phase determines the overall liquid hold-up in the pipe and the pressure losses. Besides to the fluid-dynamic issue, a better knowledge of the flow behaviour of the wall layer has many implications in flow assurance studies. In particular, the effectiveness of the inhibitors usually adopted to prevent corrosion depends on the formation of a liquid film around the pipe wall.