Structural stability and transient changes of the liquid level in stratified flow

Substantial changes of the liquid holdup along the pipe may take place due to small changes in gas or liquid flow rates. These changes can be attributed to the existence of multiple steady state solutions in stratified flow. It is aimed here to investigate the structural stability of stratified flow by applying the transient two-fluid model using the method of characteristics and to compare it to a simplified model used in the past for the structural stability analysis. It is shown here that the two approaches for structural stability analysis are consistent and in fact complement each other. The transient simulations performed with the two-fluid model have the advantage of following the transient changes in the liquid level along the pipe.