Development of new correlations for annular flow

Annular two-phase flow has been vastly investigated due to its large and deep involvement in a large amount of industrial processes, for instance, petroleum, chemical, civil and nuclear industries, and particularly in boiling and condensing heat transfer equipment. Annular flow is characterized by a thin liquid film flowing on the pipe wall and a high velocity gas core flowing in its centre, which normally carries liquid droplets. This work reviews most of the recent literature on the matter, with emphasis in all important variables which control the annular flow. This work focuses on the processes occurring in the liquid–gas interface that cause droplet entrainment, addressing also the characterization of these entrained droplets. This paper shows the existing scattering when key variables expressions are compared to each other and it highlights the gaps of knowledge still existing. Additionally, based on some of the open experimental data, alternate equations for liquid film thickness, wave celerity, wave frequency, droplet sizes and total droplet amount, have been derived for annular flow. The performance of the correlations derived is shown to enhance the existing predictability. It is noteworthy that the correlations derived are based on non-dimensional numbers, which makes them suitable for their application to a broader set of scenarios (i.e., fluids, geometry and so on)