Skip to main content

Research Repository

Advanced Search

A one-dimensional mechanistic model for tracking unsteady slug flow.

Padrino, Juan C.; Srinil, Narakorn; Kurushina, Victoria; Swailes, David; Pain, Christopher C.; Matar, Omar K.


Juan C. Padrino

Narakorn Srinil

Victoria Kurushina

David Swailes

Christopher C. Pain

Omar K. Matar


A novel one-dimensional slug tracking mechanistic model for unsteady, upward gas-liquid slug flow in inclined pipes is presented. The model stems from the first principles of mass and momentum conservation applied to a slug unit cell consisting of a slug body of liquid and a region of stratified flow containing an elongated bubble and a liquid film. The slug body front and rear are treated as surfaces of discontinuity where mass and momentum balances or "jump laws"are prescribed. The former is commonly applied in mechanistic models for slug flow, whereas the latter is typically overlooked, thereby leading to the assumption of a continuous pressure profile at these points or to the adoption of a pressure drop due to the fluid acceleration on a heuristic basis. Our analysis shows that this pressure change arises formally from the momentum jump law at the slug body front. The flow is assumed to be isothermal, the gas is compressible, the pressure drop in the elongated bubble region is accounted for, the film thickness is considered uniform, and weight effects in the pressure from the interface level are included. Besides specifying momentum jump laws at both borders of the slug body, another novel feature of the present model is that we avoid adopting the quasi-steady approximation for the elongated bubble-liquid film region, and thus the unsteady terms in the mass and momentum balances are kept. The present model requires empirical correlations for the slug body length and the elongated bubble nose velocity. The non-linear equations are discretized and solved simultaneously for all the slug unit cells filling the pipe. Timespace variation of the slug body and film lengths, liquid holdup and void fraction, and pressures, among other quantities, can be predicted, and model performance is evaluated by comparing with data in the literature.


PADRINO, J.C., SRINIL, N., KURUSHINA, V., SWAILES, D., PAIN, C.C. and MATAR, O.K. 2021. A one-dimensional mechanistic model for tracking unsteady slug flow. In Proceedings of the 2021 ASME international mechanical engineering congress and exposition (IMECE2021), 1-5 November 2021, [virtual event]. New York: ASME [online], volume 10: fluids engineering, article number V010T10A004. Available from:

Conference Name 2021 ASME international mechanical engineering congress and exposition (IMECE2021)
Conference Location [virtual event]
Start Date Nov 1, 2021
End Date Nov 5, 2021
Acceptance Date Jan 25, 2022
Online Publication Date Jan 25, 2022
Publication Date Dec 31, 2021
Deposit Date Feb 13, 2024
Publicly Available Date Mar 22, 2024
Publisher American Society of Mechanical Engineers (ASME)
Volume 10
ISBN 9780791885666
Keywords Fluid dynamics; Flow; Slug flow; Multi-phase flow; Pressure
Public URL


PADRINO 2021 A one-dimensional mechanistic (AAM) (3.1 Mb)

Copyright Statement
© ASME. All rights reserved.

Downloadable Citations