Low Dimensional Modeling of Transient Two Phase Flow in Pipelines

Abstract

Presented are reducedorder models of onedimensional transient twophase gas–liquid flow in pipelines. The proposed model is comprised of a steadystate multiphase flow mechanistic model in series with a transient singlephase flow model in transmission lines. The steadystate model used in our formulation is a multiphase flow mechanistic model. This model captures the steadystate pressure drop and liquid holdup estimation for all pipe inclinations. Our implementation of this model will be validated against the Stanford University multiphase flow database. The transient portion of our model is based on a transmission line modal model. The model parameters are realized by developing equivalent fluid properties that are a function of the steadystate pressure gradient and liquid holdup identified through the mechanistic model. The model ability to reproduce the dynamics of multiphase flow in pipes is evaluated upon comparison to olga, a commercial multiphase flow dynamic code, using different gas volume fractions (GVF). The two models show a good agreement of the steadystate response and the frequency of oscillation indicating a similar estimation of the transmission line natural frequency. However, they present a discrepancy in the overshoot values and the settling time due to a difference in the calculated damping ratio. The utility of the developed lowdimensional model is the reduced computational burden of estimating transient multiphase flow in transmission lines, thereby enabling realtime estimation of pressure and flow rate.