Investigation and prediction of slug frequency in gas/liquid horizontal pipe flow

The objective of this study is to phenomenologically investigate the parameters controlling slug frequency in horizontal two-phase pipe flow and to develop a predictive empirical correlation. In this study, two aspects governing slug frequency are investigated, namely the slug initiation mechanism at the pipe entrance region (entrance effect) and the flow development along the pipe (pipe length effect). Experimental results show that fully developed slugs generated under the hydrodynamic slugging mechanism have lower frequency than those generated under the terrain slugging mechanism for high Froude number conditions (N(Fr)>3). Conversely, fully developed slugs generated under the terrain slugging mechanism have frequency greater than those generated under hydrodynamic slugging frequency in low Froude number conditions (N(Fr)<3). Although the effect of the flow development along the pipe on slug frequency is a controversial issue in the literature, experimental data show its irrelevance to slug frequency over a wide range of operational conditions. However. experimental results show slug frequency decline along a pipeline in the case of very high liquid flow rate and very low gas flow rate and vice versa. Based on the understanding of the related physical parameters to slug frequency, a new slug frequency correlation is developed using a broad range experimental database. The developed multiple linear correlation accounts for 92% of the variation in the slug frequency in the experimental data. A validation study of the new correlation against an independent data set revealed an average error and standard deviation of 35% and 68%, respectively. A tuned version of the model using the model statistical coefficients' confidence intervals revealed improved validation results of 19% average percent error (outperforming existing correlations) and 62% standard deviation. (C) 2009 Elsevier B.V. All rights reserved.