Stratified Gas-liquid Flow Research Articles

On the effect of viscosity on stability of stratified gas—liquid flow—application to flow pattern transition at various pipe inclinations

A linear stability analysis, which takes into account the shear stresses, is presented and applied to the stability of stratified flow at various angles of inclinations. A combined model which uses the viscous and the inviscid Kelvin—Helmholtz stability analyses is suggested for the determination of the transition to slug and annular flows. The current results are compared with the simpler Taitel and Dukler model.

Stratified gas-liquid flow in downwardly inclined pipes

Measurements of liquid hold-up and pressure drop are reported for stratified flow in a slightly inclined (0.65° and 2.1°), 5 cm pipeline. Velocity profiles in the gas phase have been determined for a limited number of flow conditions. Semi-empirical correlations are proposed for the transition to slug flow, the interfacial friction factor and the liquid hold-up.

The role of interfacial friction on the shock wave propagation in stratified gas-liquid flow inside pressure tubes

The admission of the interfacial friction factor in the analysis of the shock wave propagation in the horizontal two-phase stratified flow systems is observed to weaken the shock wave travelling through the phases. A quasi-steady energy balance alludes the importance of the inclusion of the frictional loss in the shock wave phenomena in the horizontal two-phase flows. Finally the problem is dealt with a fuel bundle placed inside the pressure tube, as in a CANDU system to demonstrate experimentally the adverse effect of the pressure transients inside the fuel bundles during a LOCA (loss of coolant accident).

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.

A Study on Fluid Transient Peculiar to Gas-Liquid Stratified Two-Phase Flow : Verification of Its Existence and Examinations in Propriety of Analyses by Experiments

A Study on Fluid Transient Peculiar to Gas-Liquid Stratified Two-Phase Flow : Verification of Its Existence and Examinations in Propriety of Analyses by Experiments

Echanges de gaz dissous en ecoulements stratifies de gaz et de liquide

When carrying out experiments on absorption of oxygen or carbon dioxide in cocurrent stratified gas-liquid flows, we have determined absorption coefficient, interfacial shear stress and an interfacial roughness. Using these results, we perform a critical study of local absorption models with interfacial shear velocity and interfacial roughness as a scaling of turbulence of the liquid phase in the interfacial region. By these means we show the fundamental role of dissipative structures in absorption phenomena. We propose in conclusion a practical formula to calculate an absorption coefficient useful for very large variations of interfacial Reynolds number.

A model for stratified gas-liquid turbulent flow in ducts of arbitrary cross-section

We propose a theory to calculate the pressure gradient and the liquid fraction in two-phase gas-liquid fully developed stratified flow in a cylindrical duct of arbitrary cross-section and slope and its application to near horizontal ducts. Its validity is limited to Reynolds numbers high enough to ensure turbulent flow in both phases. Droplet entrainment or bubble inclusion have not been taken into account. The comparison between calculations and experimental values obtained with air and water in circular and rectangular ducts is very satisfactory.

One-dimensional two-fluid equations for horizontal stratified two-phase flow

Advanced computer codes for water reactor loss-of-coolant analysis are based on the use of the two-fluid model of two-phase flow, in which conservation equations are solved for the gas and liquid phases separately. The standard two-fluid equations, however, sometimes predict the growth of instabilities in the flow, and occasionally become improperly posed. These difficulties have in the past led to the proposal of several different forms for the conservations equations. To help resolve these uncertainties a widely accepted form of the one-dimensional two-fluid equations is used to calculate wave propagation speeds, and stability limits, for the illustrative case of a frictionless horizontal stratified gas-liquid flow. Calculated propagation velocities are shown to agree with the appropriate limit of an exact solution, and the predicted stability limits are found consistent with available observations on the stability of the stratified flow regime. These comparisons help improve confidence in the ability of the two-fluid equations to analyse more complex problems in transient two-phase flow.

Mass transfer by cocurrent gas-liquid stratified flow

Mass transfer by cocurrent gas-liquid stratified flow

Mass transfer by cocurrent gas-liquid stratified flow

Mass transfer by cocurrent gas-liquid stratified flow

Laminar boundary layers of co-current gas-liquid stratified flows—II. Velocity measurements

An experimental investigation of the velocity distribution in the laminar boundary layer at a moving interface in co-current gas-liquid flow has been made. The velocity profiles were measured by hot wire technique at different distances from the initial phase interaction location. The experimental results compare well with theoretical predictions which are solutions of the Prandtl's equations.

Laminar boundary layers of co-current gas-liquid stratified flows—I. Theory

The flow in the developing laminar boundary layers on a flat moving gas-liquid interface is studied theoretically. Analysis of the equations shows that flows depend on two parameters, each less than unity. Using a perturbation method, an analytical solution with accuracy to the third power of the small parameters is obtained and is in close agreement with the exact solution of the problem.

Laminar boundary layers at a moving interface generated by counter-current gas-liquid stratified flow

An experimental and theoretical investigation of the velocity distribution in the laminar boundary layers at a moving interface generated by a counter-current gas-liquid stratified flow has been made. No similarity solution of the problem exists, as in the case of co-current motion of the phases. The solution is carried out by means of the perturbation method. A comparison of the theoretical results with experimental ones obtained by the use of hot-wire technique is performed.

The onset of natural convection and its enhancement of heat transfer in stratified gas-liquid flow

The results of heat-transfer experiments and flow visualization studies are presented, showing the onset of natural convection in the liquid layer of a horizontal stratified gas-liquid flow heated from below by means of a step change in the wall heat flux. The Nusselt numbers, Nu, for combined free and forced convection are shown to be functions of the Rayleigh number, Ra q , and the dimensionless axial distance, ξ. The data on the enhancement of heat transfer over that for the undisturbed flow (a Graetz problem) are well correlated by the dimensionless parameter ø = (Ra q/Nu) 1 4 /Nu Gz . The onset of natural convection occurs at ø = 2.+8 for the narrow range of Prandtl numbers studied (5 < Pr < 8), which is in good agreement with an available theoretical analysis of the onset of natural convection in channels of rectangular cross-section.

On the motion of a two-component stratified gas-liquid flow in a horizontal pipe

On the motion of a two-component stratified gas-liquid flow in a horizontal pipe

Surface Waves and Surfactant Effects in Horizontal Stratified Gas-Liquid Flow

Surface Waves and Surfactant Effects in Horizontal Stratified Gas-Liquid Flow

The enhancement of heat transfer by waves in stratified gas-liquid flow

An experimental investigation of heat transfer from a flat plate to horizontal cocurrent airwater flow has been carried out to assess the effects of the different flow regimes on the effectiveness of the heat transfer. The results for smooth liquid film flow and two-dimensional wavy flow of the liquid phase are shown to agree with the theoretical analysis of heat transfer to smooth films. Three-dimensional waves and roll waves are shown to increase the Nusselt number (compared with smooth films) by more than 100 per cent. By using a surface-active agent to stabilize the flow direct comparison between wavy flow heat transfer and smooth flow heat transfer is obtained. At sufficiently low gas phase Reynolds numbers and at sufficiently high wall heat fluxes Rayleigh-like instability due to buoyant forces is shown to occur.

Thermal entrance effects in stratified gas—liquid flow: experimental investigation

A study of heat transfer in the thermal entrance region for horizontal concurrent airwater flow over a flat plate has been carried out to complement theoretical studies of the phenomenon. Measurements of the heat transfer characteristics and fluid mechanics parameters have been made for constant wall temperature and constant wall heat flux boundary conditions. The results for smooth surfaces and for hydrodynamically unstable liquid films are compared with the theory for non-rippling films. Theory and experiment are compared in terms of dimensionless parameters that characterize the system, in terms of wall temperature and wall heat flux profiles and as local Nusselt numbers vs. position.