Transient gas/liquid two-phase flow in a pipeline-riser system after the change of inlet flow rates

Transient gas/liquid two-phase flow caused by the change of inlet gas and/or liquid flow rates was experimentally studied in a 380-meter-long pipeline-riser system with a vertical riser of 21.5 meters in height. Results showed that, for the transient processes with the same median flow rates, the rise of flow rates was likely to result in shorter duration time compared to the fall of flow rates. Apart from the manner of change, the duration time was also closely related to the flow mechanism, which varied with the global flow regime. As a consequence, the transient process lasted a longer time around the transition boundary of stable regime and the severe slugging regime; whereas, the transient process would be shorter if the regime was an irregular oscillation; and the longest transient process was found at very low gas and liquid flow rates. As for the prediction of duration time of both the entire transient process and the transition to undesirable flow regimes, the support vector machine turned out to be much more suitable than the log-linear regression. In addition, some similarities of pressure drop signals were found between the transition to unstable and irregular flow regimes and the steady state of these regimes. Since the method for fast recognition of a steady global flow regime has already been developed, it becomes possible to forecast the transition to these undesirable flow regimes through the modification of the recognition method.