Assessment of two-phase slug frequency correlations in horizontal pipes under different operational conditions

Accurate prediction of the slug frequency in horizontal pipe flow is essential for appropriate design and operation in various industrial processes. This study provides a comprehensive review of existing empirical correlations for slug frequency in horizontal pipes, highlighting their limitations and applicability. A total of 36 correlations were examined, and 1083 data points were collected from experiments using pipes with inner diameters ranging from 3.7 to 150 mm. The correlations were categorized based on pipe diameter and gas–liquid working fluids. The correlations based on the Froude number had the best performance for superficial liquid velocities within the range of v_SL = 0.502–1.505 m/s, with a maximum mean relative difference (MRD) of ±30% and a mean absolute relative difference (MARD) of 40% for superficial gas velocities v_SG greater than 1 m/s. The Strouhal number produced the most effective correlations for most of the datasets examined in slug frequency testing. In contrast, the air–oil slug frequency correlations were unable to accurately predict the air-water experimental data, except for that of Al-Safran (2016), which was limited to small-diameter pipes. 909 data points were used to evaluate slug frequency for high viscous fluids; the results showed that the correlation of Baba et al. (2017) provided the best prediction performance, with a maximum MRD of 30%.