Annular liquid film thickness prediction in a vertical 180° return bend

Annular flow is predominant in gas wells. Liquid may be present in form of entrained droplets as well as in the liquid film on pipe wall. The knowledge of the average liquid film thickness is vital for detailed mechanistic modelling of churn-annular flow in engineering applications. So far, the models for liquid film thickness prediction are limited to vertical and horizontal pipes. These models were based on limited ranges of experimental data. In addition, exhaustive iterations are needed when these models are used to estimate liquid film thickness. In this work, a new correlation to predict liquid film thickness in a 180° bend under gas-liquid annular conditions was successfully proposed. The correlation was based on dimensionless numbers (modified gas and liquid Weber numbers and gas Froude number) which reflect the underlined physics governing gas-liquid interaction in the bend. The Weber numbers capture the two important forces (inertial and surface tension forces) which govern the formation of the liquid film thickness within the system while gas Froude number quantifies the interaction of two important forces (centrifugal and gravitational forces) which determines the distribution of the phases across a bend. The proposed liquid film thickness correlation was based on the experimental data obtained from a wide range of operating conditions. The liquid superficial velocities ranges from 0.02 to 0.2 m/s and gas superficial velocities from 3.5 to 16 m/s at different measurement locations of 45°, 90° and 135° of the bend with a diameter of 127 mm. The liquid film thickness in air-water and helium-water annular flow can be predicted by δ=28.4061(WeL)0.10318(WeG)-0.30954(FrG)-0.31423. The validation of the proposed correlation used to predict liquid film thickness in gas-liquid annular systems with different pipe diameters were examined against the available data in the literature. Good agreement was found between the predicted values of liquid film thickness with the experimental data at different measuring locations of the bend.