Over ten different slug frequency models/correlations were evaluated against experimental data as a part of this study. The effect of parameters such as pressure and flow development length on slug frequencies were studied and comparisons with model predictions were made. The available slug frequency models have all been developed for smaller diameter pipes. Comparison of model predictions for 6 in. ID pipe with the experimental results has shown that none of the existing slug frequency models could predict the experimental results with even moderate accuracy. The empirical nature of the current slug models is the main reason for their poor performance. This study also shows significant gaps in the existing slug frequency models/correlations, namely:
The pipe diameter effect: None of the models/correlations can be used with confidence in the industry for large diameter pipelines.
Effect of flow development length: Many models/correlations neglect the effect of flow development length on slug frequencies. The experimental study has revealed that this is an important parameter.
Slug flow is a very common flow pattern in pipelines and wellbores. It is characterized by an alternating liquid slug and gas bubble configuration. Slug frequency models are used as input parameters in several mechanistic slug flow models, such as Dukler and Hubbard (1975), Taitel and Barnea (1990), Sylvester (1987), Felizola and Shoham (1995), etc. Thus, the use of an accurate slug frequency model can potentially result in better pressure gradient predictions by the aforementioned slug flow models. Prediction of slug frequency is also important from a materials standpoint, as slugging can significantly increase erosion, corrosion, and fatigue in pipelines. In the following section, an overview of the slug frequency models reviewed in this study is presented.