Session: 08-07-01 Internal Flows & Fluid–Structure Interaction in Riser and Pipeline Systems

Submission Number: 181156

On the 1D Mathematical Modeling of Moving Liquid Slugs
and Gas Columns 

One-dimensional (1D) mathematical models have several advantages compared to three-dimensional (3D) CFD (computational fluid dynamics) simulations: the computation times are much shorter, the results are easier to understand and interpret (and therefore suitable for educational purposes), analytical solutions are (sometimes) possible.

A 1D model describing the propagation of individual liquid slugs in pipelines is presented.  These slugs are dangerous when hitting obstacles like orifices and bends.  The modelling of discontinuities at liquid-gas interfaces involves some fundamental issues.  Gas intrusion, momentum mixing, liquid holdup, friction and drag: all need special attention.   Underlying assumptions are verified in terms of length and time scales.  Validation of the model is against old and new experimental results.  In the old experiment, compressed air is used to shoot a single water slug into an upward sloping pipe with elbow and orifice at its upper end.  The test setup concerns a 12 m long pipe of 0.1 m diameter connected to a 0.5 m³ air vessel.  The 10 to 50 kg heavy slugs are initially at rest in the lower part of the system.  Because the upper end is closed by a flange with orifice, the water slug is expected not to hit the upstream elbow.  It causes - like a piston - a fast compression of the air column ahead of it.  Sometimes the slug bounces back and forth, which results in a pressure oscillation of serious amplitude.  The new experiment is in a 30 m long pipe with open end in which slug velocities up to 100 m/s were observed.

The model can also be applied to the rapid filling and emptying of pipes.  The research is of importance - next to water and air or oil and gas - for steam lines where liquid condensates may collect in lower parts after power failure.  Start-up of the system will then lead to rapid slug acceleration and potentially damaging impact on elbows, orifices, and machinery.

Presenting Author: Arris S. Tijsseling Eindhoven University of Technology

Presenting Author Biography: Arris Tijsseling is Associate Professor at Eindhoven University of Technology in The Netherlands.

Authors:

Arris S. Tijsseling Eindhoven University of Technology
Arnout M. Klinkenberg Equinor