Jorge Luis Baliño

Modeling and simulation of severe slugging in air-water systems including inertial effects

Abstract A mathematical model and numerical simulations corresponding to severe slugging in air-water pipeline-riser systems are presented. The mathematical model considers continuity equations for liquid and gas phases, with a simplified momentum equation for the mixture. A drift-flux model, evaluated for the local conditions in the riser, is used as a closure law. In many models appearing in the literature, propagation of pressure waves is neglected both in the pipeline and in the riser. Besides, variations of void fraction in the stratified flow in the pipeline are also neglected and the void fraction obtained from the stationary state is used in the simulations. This paper shows an improvement in a model previously published by the author, including inertial effects. In the riser, inertial terms are taken into account by using the rigid water-hammer approximation. In the pipeline, the local acceleration of the water and gas phases are included in the momentum equations for stratified flow, allowing to calculate the instantaneous values of pressure drop and void fraction. The developed model predicts the location of the liquid accumulation front in the pipeline and the liquid level in the riser, so it is possible to determine which type of severe slugging occurs in the system. A comparison is made with experimental results published in literature including a choke valve and gas injection at the bottom of the riser, showing very good results for slugging cycle and stability maps. Simulations were also made assessing the effect of different strategies to mitigate severe slugging, such as choking, gas injection and increase in separation pressure, showing correct trends.

Modeling One-Dimensional Incompressible Duct Flows

In this paper a Bond Graph methodology described in a previous contribution is used to model incompressible one-dimensional duct flows with rigid walls. Since the volumetric flow is independent of position, the balance equations can be simplified. The volumetric flow and a nodal vector of entropy are defined as Bond Graph state variables. The state equations and the coupling with the inertial and entropy ports are modeled with true bond graph elements. Keywords— Bond Graphs, incompressible flow, one-dimensional duct flow, Finite Elements.

Linear stability analysis for severe slugging: sensitivity to void fraction and friction pressure drop correlations

In this paper a numerical linear stability analysis is performed on a mathematical model for the two-phase flow in a pipeline-riser system. Void fraction is a key variable, as it influences the mixture properties and slip between the phases. Friction two-phase pressure drop is also an important variable as it is necessary, for instance, to determine the pumping power in multiphase processes. For a correct prediction of the stability behaviour of a pipeline-riser flow, preventing the occurrence of severe slugging, it is important to assess the sensitivity of the system response to different void fraction and friction pressure drop correlations. Three void fraction (Bendiksen, 1984; Chexal et al., 1997; Bhagwat and Ghajar, 2014) and two friction pressure drop correlations [homogeneous and Muller-Steinhagen and Heck (1986)] are implemented. The resulting stability maps and state variables profiles for vertical risers are compared for the different correlations. For the void fraction sensitivity study, results show that the different correlations give similar stability maps, with very small differences in the near horizontal branch (low gas superficial velocities) of the stability boundary and slight differences in the near vertical branch (low liquid superficial velocities). For the friction pressure drop sensitivity study, results show that it does not affect significantly the stability maps because the mass fluxes are low and the main contribution to the total pressure drop comes from the gravitational term. The different correlations show the right experimental trend by increasing the unstable region as the equivalent buffer length in the pipeline is increased.

Finite Element Formulation for Computational Fluid Dynamics Framed Within the Bond Graph Theory

A true bond graph based methodology is used to frame a Finite Element formulation for Computational Fluid Dynamic problems. A single-phase, single-component, multidimensional compressible flow with viscosity and thermal effects is considered first, resulting state equations in terms of nodal vectors of mass, velocity, and entropy. The methodology is also applied to an incompressible flow, showing the role of pressure as external function acting to satisfy the incompressibility condition; for this case, the state equations are expressed in terms of nodal vectors of pressure, velocity, and entropy. A Galerkin method results for the linear momentum equation, while Petrov–Galerkin method results for the mass (or pressure, in case of incompressible flow) and entropy balance equations.

Assessment of Uncertainties and Parameter Estimation in a Offshore Gas Pipeline

Natural gas has a great importance in actual economy, and its transport is done usually through pipeline networks. The operation of a gas pipeline uses numerical models for calculation of intermediate properties, prediction of future behavior and estimation of the integrated flow capacity. These models are based on physical assumptions, closure laws and field measurements of boundary conditions such as pressure, flow, temperature and composition of the natural gas. This paper presents a development proposed for state and parameter estimation based on the implementation of an extended Kalman filter, in order to determine appropriate values for the flow parameters and use of complementary measurements in the boundary conditions. These results are compared to the ones obtained by using the Equal Error Fraction Method. It was found reduced pressure and flow systematic errors when the Kalman filter was used to estimate parameters.