The knowledge of the flow characteristics of a two-phase pipeline under transient flow or pigging operation is essential for a proper design and operation of the pipeline and the upstream and downstream facilities. An existing simplified model for predicting two-phase transient flow behavior that uses physically-based, flow pattern-dependent mechanistic models has been modified and improved. Also, a new pigging model to simulate the dynamics of pigging operation has been developed. The resulting set of differential equations is solved numerically utilizing a mixed Eulerean-Lagrangean approach. The discretization of the transient model equations is performed using an Eulerean (fixed) coordinate grid system, and the pigging model equations using a Lagrangean (moving) grid system. The computer simulator that couples the transient model and the pigging model is capable of predicting the overall flow behavior of a two-phase pipeline under transient condition, with or without pigs.;An extensive experimental program has been carried out to acquire two-phase transient flow and pigging data on a 420 m (1,378 ft) long, 77.9 mm (3.068 in) diameter horizontal pipeline. A computer based data acquisition system has been utilized to obtain rapidly changing and detailed information of the flow behavior during the transient tests. Pressure, in-situ liquid holdup, translational velocity and flow pattern changes were monitored at four measurement stations installed along the pipeline. Comparisons of the predictions of the numerical model against the experimental data show that the proposed simplified transient model and the pigging model are well suited for simulating the type of transient behavior observed in two-phase pipelines in the petroleum industry.
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