On gas-liquid intermittent flow in a horizontal pipe: Influence of sub-regime on slug frequency

[Display omitted] •Experimental investigation of the slug frequency of various sub-regimes.•Comparison between various methods of slug frequency measurements using differential pressure signals.•A new flow map for the sub-regimes distinction was developed.•A new slug frequency correlation for the sub-regimes of the intermittent flow was developed. Among the intrinsic parameters identified in intermittent gas-liquid flows; slug frequency is known as the most complicated one to model. The present work concerns the investigation of slug frequency for various sub-regimes which might be found in intermittent flow. Experiments, near atmospheric pressure conditions, were carried out in a 13-meter long horizontal pipe with a 30 mm inside diameter. The study involved plug regime, less aerated slug and highly aerated slug flows. Comparison between different methods of slug frequency quantification, from pressure drop signal, was performed with counting, Wilkens & Thomas as well as the Power Spectral Density (PSD) methods. PSD was found to be the best method for slug frequency measurements. A new flow map, using dimensionless numbers as coordinates for the sub-regimes distinction, was established. After performing substantial comparisons between the present results and models available in the literature a new correlation is proposed including the sub-regime types.