Stratified Gas Liquid Two-phase Flow Research Articles

Experimental Investigation of Different Sub-Regimes in Horizontal Stratified and Intermittent Gas-Liquid Two-Phase Flow: Flow Map and Analysis of Pressure Drop Fluctuations

Experimental Investigation of Different Sub-Regimes in Horizontal Stratified and Intermittent Gas-Liquid Two-Phase Flow: Flow Map and Analysis of Pressure Drop Fluctuations

Corrosion behavior of 20# steel in aqueous CO2 solution under stratified gas-liquid two-phase flow condition

PurposeThis paper aims to investigate the corrosion rate, surface morphology and composition of corrosion products of 20# seamless steel in aqueous CO2 solution under stratified gas-liquid two-phase flow condition. The development of a corrosion products layer has also been discussed.Design/methodology/approachThe following methods were used: weight loss method, scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction.FindingsThe corrosion rate curve presents an irregular zigzag change trend with a gradual increase in time. The peak value of the corrosion rate appears when the corrosion time is 4 h and 8 h. The corrosion products layer is composed of two sub-layers: the inner dense layer that is about 6 µm thick and the outer loose layer that is about 9 µm thick when the corrosion time is 8 h. The main corrosion product are FeCO3 and Fe2O3.Originality/valueThe atomic ratio of Fe/C/O is relatively stable for the inner dense layer, but changes in thickness for the outer loose layer. There is a densification stage after a loose corrosion products layer forms, and it is periodic.

A horizontal stratified gas–liquid two-phase flow model for the two-fluid model in the WCOBRA/TRAC-TF2 PWR safety analysis code

For the two-phase flow in a horizontal pipe, individual phases may separate because of gravity. This horizontal stratification significantly impacts interfacial drag, interfacial heat transfer and wall drag of the two-phase flow. Due to the low interfacial drag and the low interfacial heat transfer, the horizontal stratification in reactor coolant systems is a highly important phenomenon during a postulated loss-of-coolant accident in PWR. The horizontal stratification also impacts other SBLOCA phenomena such as the offtake phenomenon and the cold leg direct contact condensation phenomenon.For the two-fluid model in the WCOBRA/TRAC-TF2 LOCA safety analysis computer code, a horizontal stratification criterion was developed following the inviscid Kelvin–Helmholtz neutral stability analysis. The horizontal stratification criterion combines the Taitel–Dukler model and the Wallis–Dobson model and captures the test data better. The stratification criterion was assessed against various experimental data with a wide range of pressures and pipe sizes. The stratification criterion also matches well with the transition boundaries predicted by the viscous Kelvin–Helmholtz model.The adequacy of the horizontal stratification model is confirmed by examining the predicted flow regime in a horizontal pipe with the measured data of the high pressure TPTF two-phase flow experiments. The void fractions for the horizontal flow are predicted with a good accuracy, which indicates that the interfacial drag and the wall drag in the two-fluid model are properly modeled and the two-fluid momentum equations with the hydraulic slope term reasonably capture the influence of inlet and outlet boundary conditions expected in the PWR LOCA simulation.

Heat transfer for fully developed stratified wavy gas–liquid two-phase flow in a circular cross-section receiver

Stratified gas–liquid two-phase flow occurs during the direct steam generation in the receivers. In order to understand how such a receiver can work under stratified two-phase flow regime forms, the numerical modeling of fully developed stratified wavy gas–liquid flow in a circular cross-section receiver is presented. The steady-state axial momentum and energy equation are coupled and solved together with a low Reynolds number k∼ɛ turbulence model for the eddy viscosity. The interface boundary conditions are more complex in the wavy flow than the smooth due to the unsteadiness of the wave motion itself. It is found that the interface configuration and wavy character must be taken into accounted for hydro and heat transfer simulation to be valid. Unfortunately, this has not been accounted for in all previous studies. The boundary conditions for the wave gas–liquid interface are devised from empirical consideration. In hydro dynamic simulation, the numerical calculations of global properties, such as pressure gradient and liquid holdup, shear stress distribution and the velocity field have been compared with the experimental data. In addition, for heat transfer simulation, the predictions of bulk and inside receiver wall temperature have been compared with the experimental result. It is concluded that a perfect agreement between this numerical calculation and experimental results could be achieved.

Experimental and Numerical Investigation of Stratified Gas–Liquid Flow in Downward-Inclined Pipes

This paper reports an experimental and numerical investigation of stratified gas–liquid two-phase flow in downward-inclined circular pipes. Reynolds averaged Navier–Stokes equations with the κ–ω turbulence model were solved by using the least-square finite-element method to simulate the stratified gas–liquid flow. Experiments were carried out in an air–water two-phase flow loop with a test section of 7.8-m-long circular pipe with 1 inch inner diameter for 3 downward-inclined angles, −2.5°, −5.0°, and −10.0°. The height of the liquid layer was measured by using a pulse–echo ultrasonic technique with a single fast transducer and a visualization technique with a high-speed digital camera. Numerical results for the liquid height and hold-up as a function of inclination angles were compared favorably with experimental results of the present study and literature data.

Interfacial shear stress in wavy stratified gas–liquid flow in horizontal pipes

The scope of this study was to improve the Andritsos-Hanratty model for estimating interfacial friction factor and pressure drop in horizontal stratified gas–liquid two-phase flow. New experimental results (focusing on the effects of gas density and surface tension), combined with experimental data available in the literature, permit the development of semi-theoretical correlations for the transition from smooth stratified to 2-D wave region and from the latter to large-amplitude wave region and of different empirical relations for the interfacial friction factor in the two wave regions. The transition correlations agree reasonably well with existing and new data obtained in this work and the modified relations give improved predictions for both liquid holdup and pressure drop during gas–liquid stratified flow in horizontal and slightly downward pipelines as deduced from a statistical analysis of the results.

Modelling of stratified gas–liquid two-phase flow in horizontal circular pipes

This paper reports numerical and experimental investigation of stratified gas–liquid two-phase flow in horizontal circular pipes. The Reynolds averaged Navier–Stokes equations (RANS) with the k– ω turbulence model for a fully developed stratified gas–liquid two-phase flow are solved by using the finite element method. A smooth interface surface is assumed without considering the effects of the interfacial waves. The continuity of the shear stress across the interface is enforced with the continuity of the velocity being automatically satisfied by the variational formulation. For each given interface position and longitudinal pressure gradient, an inner iteration loop runs to solve the non-linear equations. The Newton–Raphson scheme is used to solve the transcendental equations by an outer iteration to determine the interface position and pressure gradient for a given pair of volumetric flow rates. Favorable comparison of the numerical results with available experimental results indicates that the k– ω model can be applied for the numerical simulation of stratified gas–liquid two-phase flow.

A linear and non-linear analysis on interfacial instability of gas–liquid two-phase flow through a circular pipe

A linear instability analysis was conducted firstly on the interface of a stratified gas–liquid two-phase flow in a circular piper employing a two-fluid model. The constitutive equations simulation technique was discussed, and the dispersive equation of interfacial waves was derived. The effects of flow rates of gas and liquid, liquid viscosity, surface tension and tube inclination on the stability of interface were investigated. A set of non-linear hyperbolic governing equations was deduced from the complete two-fluid model equation by omitting the effect of the surface tension and assuming a quasi-steady-state for the gas phase. Using characteristic line and finite difference, the propagation and growth of the interfacial disturbances were investigated in terms of gas and liquid superficial velocities. Then the results of the non-linear stability analysis were compared with those obtained by the linear stability analysis and experimental data. The non-linear stability analysis not only confirms the conclusions reached by the linear instability analysis, but also gives an insight into the growth and propagation of the interfacial disturbances on the interface of a gas–liquid two-phase flow.

Mechanistic Model of Slugging Onset in Horizontal Circular Tubes

A new model of the transition mechanism from stratified gas-liquid two-phase flow into a slug pattern in horizontal circular tubes was developed. This model incorporated the contribution of liquid kinematic energy to wave growth on the interphase surface. The transition limit was numerically determined so as to allow a wave crest to reach the top wall of the horizontal tubes. Air-water experiments were performed to obtain data for comparison with model predictions. Three test sections were used. They had different inner diameters and the largest test section had a rod bundle inside it. Predictions of liquid flow rate at the flow pattern transition boundary, with given gas flow rates, were within data scatter of the experiments. This suggested that the present model satisfactorily described effects of tube size and internal structure on slugging onset in horizontal circular tubes.

Mechanistic model of slugging onset in horizontal circular tubes.

A new model of the transition mechanism from stratified gas-liquid two-phase flow into a slug pattern in horizontal circular tubes was developed. This model incorporated the contribution of liquid kinematic energy to wave growth on the interphase surface. The transition limit was numerically determined so as to allow a wave crest to reach the top wall of the horizontal tubes. Air-water experiments were performed to obtain data for comparison with model predictions. Three test sections were used. They had different inner diameters and the largest test section had a rod bundle inside it. Predictions of liquid flow rate at the flow pattern transition boundary, with given gas flow rates, were within data scatter of the experiments. This suggested that the present model satisfactorily described effects of tube size and internal structure on slugging onset in horizontal circular tubes.