Limited results for gas-oil mixtures are also presented. A complete set of data, in which concerns to the flow structure, was acquired with mixtures of air and water. Two transducers measured the differential pressure across the pipe diameter at two distinct axial positions and a third transducer measured the pressure drop between two sections 200 meters apart. To identify and measure the structure of the slug flow, i.e., frequency and velocity of the unit cell, the length of the liquid slug and elongated bubble and the pressure drop, one registered and processed the signal delivered by pressure transducers. The objective of this work was directed toward this lack: one presented a set of measurements carried on a 6 inches horizontal pipeline, 200 m long, which is part of the test rig of Atalaia, operated by Petrobras. Only a few data were collected in large-scale facilities (Gregory et al., 1978 and Gonçalves et al., 1996). However, the great majority of published data on the slug flow characteristics were taken in small-scale laboratory facilities, running with mixtures of air and water. These semi-empirical models rely, for development and comparison, on data bases generated by experimentation. The slug flow models based on the unit cell concept (Dukler and Hubbard, 1975 and Nicholson et al., 1978) are quite usual nowadays, composing some of the commercially available codes used by the oil industry to calculate two-phase flow facilities.
The large amount of published papers presenting measurements and discussing the modelling of slug flows reflects the fact that this is the flow pattern that most frequently occurs in petroleum pipelines. The velocity of the unit cell, for example, determines the instantaneous gas and liquid flow rate delivered to a receiving vessel the length of the liquid slug correlates strongly with the pressure drop. Hence, the knowledge of the characteristics of the slug flow pattern, i.e., the frequency and velocity of the unit cell and the length of the liquid slug and elongated bubble, among other variables, is very important when sizing pipelines and designing receiving vessels and pre-processing equipment. These singular structures succeed each other in the test section in an intermittent fashion, causing a fluctuation in the flow variables: velocities, flow rates, pressure gradients. The most used mechanistic representation of the slug flow is the unit cell model: the flow unit is composed of an aerated liquid slug and an elongated bubble.
Keywords: Slug flow, gas-liquid intermittent flow, two-phase flow instrumentation Slug flow gas-liquid intermittent flow two-phase flow instrumentation
The experimental data were compared with results of Camargo's1 algorithm (1991, 1993), which uses the basics of Dukler & Hubbard's (1975) slug flow model, and those calculated by the transient two-phase flow simulator OLGA. A third pressure transducer measured the pressure drop between two axial location 200 m apart. To compute the frequency and velocity of the slug cell and to calculate the length of the elongated bubble and liquid slug one used two pressure transducers measuring the pressure drop across the pipe diameter at different axial locations. Experiments were done with natural gas and oil or water as the liquid phase. The results were compared with data provided by mechanistic slug flow models in order to verify their reliability when modelling actual flow conditions. Focusing on this subject the present work discloses the experimental data on slug flow characteristics occurring in a large-size, large-scale facility. When the intermittences typical in slug flow occurs, the fluctuations of the flow variables bring additional concern to the designer. The knowledge of the slug flow characteristics is very important when designing pipelines and process equipment.