(An) analysis of the stratified and nonstartified flow transition criterion in horizontal/inclined pipes

Abstract

The present studies are developed to present the two-step approach which is used in extending the phase-plane method and the hyperbolicity breaking concept for instability analyses of one-dimensional two-phase flow equations to the derivations of the new criterion for the stratified and non-stratified flow transition (e.g., onset of slugging), the critical flow condition criterion, and the flooding criterion. In the first step, more general forms for the onset of slugging critertion, the critical flow condition criterion, and the flooding criterion are derived based on the nonlinear analysis: more specifically, analyses of the phase-plane method and hyperbolicity breaking concept of the "inflected nodes" (neutral stability conditions) and "parallel lines" in the topological patterns of the linear system obtained from the transient one-dimensional two-phase flow equations of a two-fluid model. In the second step, through the introduction of simplifications and incorporation of a parameter (at the onset of slugging criterion) or an empirical constant (at the flooding criterion) into the general expression derived in the first step to satisfy a number of physical conditions a priori specified, new criteria for the onset of slugging and the onset of flooding have been derived. Validation of the present stratified and non-stratified flow transition criterion is achieved by comparison with the existing analytical criteria (Taitel & Dukler model and one-dimensional wave model) and experimental data from large test facilities (IFP, SINTEF, Harwell, Creare/PRC, ROSA & UPTF). The result of the validation shows good agreement at large pipe diameters and at high gas velocities. Present studies have revealed that the two-phase density ratio and pipe inclination angle are very important parameters that should be handled properly to determine the flow regime boundary correctly. Comparison between the present critical flow condition criterion with Gardner``s critical flow co...