Intermittent gas-liquid flow in upward inclined pipes

Experimental measurements of flow patterns. pressure gradients and liquid holdup for intermittent two-phase flow in upward inclined pipes are reported. Comparison of this new experimental evidence is made with the Taitel & Dukler theory and the intermittent flow model as modified by Nicholsonet al.     

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.     

Flow pattern transition for gas-liquid flow in a vertical rod bundle

Experimental and analytical studies are presented directed to the prediction of flow pattern transitions in a vertical rod bundle array. The test section used consists of a 24 rod matrix on a square pitch in a cylindrical shell. Analytical models are given based on physical interpretation of the transition mechanisms. Data on rise velocities of small and large bubbles in rod bundles are also presented.     

Comparison of void fraction correlations for different flow patterns in horizontal and upward inclined pipes

A comparison of the performance of 68 void fraction correlations based on unbiased data set (2845 data points) covering wide range of parameters than previous assessments was made. A comprehensive literature search was undertaken for the available void fraction correlations and experimental void fraction data. After systematically refining the data, the performance of the correlations in correctly predicting the diverse data sets was evaluated. Comparisons between the correlations were made and appropriate recommendations drawn. The analysis showed that most of the correlations developed are very restricted in terms of handling a wide variety of data sets. Based on the observations made, an improved void fraction correlation which could acceptably handle all data sets regardless of flow patterns and inclination angles was suggested. It was shown that this correlation has the best predictive capability than all the correlations considered in this study.     

Pressure drop in two phase gas-liquid flow in inclined pipes

Two phase pressure loss data are presented for angles from vertical upward to vertical downward for co-current air-water flow in a 4.55 cm diameter pipe operating at about atmospheric pressure. Detailed comparison with data from the literature indicated a substantial measure of agreement and showed that the method of data presentation suggested eliminates any effect on pressure loss of diameter, liquid density and system, but not that of liquid phase viscosity: Specific details are given on aspects of the measured frictional pressure loss from which it is deduced how energy losses can be minimised in two phase systems. In particular a total flow velocity of 15 ms^?1 is recommended for most flow conditions in order to give a balance between flow capacity of the equipment and pressure loss.     

A model for slug frequency during gas-liquid flow in horizontal and near horizontal pipes

Slug formation is an entry region phenomena. Waves form on a growing stratified film eventually blocking the gas to form a slug. The liquid level drops when the slug is swept away and the waves disappear. Then the film rebuilds its level in a time equal to the inverse frequency. The process is modelled and the results shown to be in agreement with experiment.     

An improved semi-empirical friction model for gas-liquid two-phase flow in horizontal and near horizontal pipes

Pressure drop and liquid hold-up are two very important fluid flow parameters in design and control of multiphase flow pipelines. Friction factors play an important role in the accurate calculation of pressure drop. Various empirical and semi-empirical closure relations exist in the literature to calculate the liquid-wall, gas-wall and interfacial friction in two-phase pipe flow.However most of them are empirical correlations found under special experimental conditions. In this paper by modification of a friction model available in the literature, an improved semiempirical model is proposed. The proposed model is incorporated in the two-fluid correlations under equilibrium conditions and solved. Pressure gradient and velocity profiles are validated against experimental data. Using the improved model, the pressure gradient deviation from experiments diminishes by about 3%; the no-slip condition at the interface is satisfied and the velocity profile is predicted in better agreement with the experimental data.     

A flow pattern map for gas—liquid flow in horizontal pipes

Various flow pattern maps for two-phase gas—liquid flow in horizontal pipes are tested against the 5935 flow pattern observations presently contained in the UC Multiphase Pipe Flow Data Bank.A new flow regime correlation representing an extension of the work done by Govier and Aziz [3] is presented and is shown to be in better agreement with the data than the other correlations tested. A computer program for this correlation is included.It is also shown that there is no significant improvement obtained by including the effects of the physical properties of the fluids using any of the physical property parameters which have been proposed so far.     

Experimental study on oil–water flow in horizontal and slightly inclined pipes

Oil–water two-phase flow experiments were conducted in a 15 m long, 8.28 cm diameter, inclinable steel pipe using mineral oil (density of 830 kg/m³ and viscosity of 7.5 mPa s) and brine (density of 1060 kg/m³ and viscosity of 0.8 mPa s). Steady-state data on flow patterns, two-phase pressure gradient and holdup were obtained over the entire range of flow rates for pipe inclinations of −5°, −2°, −1.5°, 0°, 1°, 2° and 5°. The characterization of flow patterns and identification of their boundaries was achieved via observation of recorded movies and by analysis of the relative deviation from the homogeneous behavior. A stratified wavy flow pattern with no mixing at the interface was identified in downward and upward flow. Two gamma-ray densitometers allowed for accurate measurement of the absolute in situ volumetric fraction (holdup) of each phase for all flow patterns. Extensive results of holdup and two-phase pressure gradient as a function of the superficial velocities, flow pattern and inclinations are reported. The new experimental data are compared with results of a flow pattern dependent prediction model, which uses the area-averaged steady-state two-fluid model for stratified flow and the homogeneous model for dispersed flow. Prediction accuracies for oil/water holdups and pressure gradients are presented as function of pipe inclination for all flow patterns observed. There is scope for improvement for in particular dual-continuous flow patterns.     

On the transition between slug flow and two-layer flow of a gas-liquid mixture in a horizontal tube

The conditions necessary for the existence of slug flow are considered and the boundary of the region of its existence is constructed. Comparison with the author's own data and published experimental data reveals agreement of the results.     

A three-layer model for solid-liquid flow in horizontal pipes

A three-layer model for solid-liquid flow in horizontal pipes is proposed. This model overcomes the limitations of the two-layer model. The model predictions exhibit satisfactory agreement with the experimental data and existing correlations.     

Flow pattern,void fraction and pressure drop of refrigerant two-phase flow in a horizontal pipe—I. Experimental data

Experiments with refrigerant two-phase flow in a horizontal pipe have been performed and data on flow pattern, void fraction and pressure drop have been obtained. Refrigerants used were R12 and R22, and the range of saturation pressure was from 5.7 to 19.6 bar.In this paper, the experimental equipment and procedure are described in detail, and the data are both tabulated and presented graphically.     

Drift-flux correlation for gas-liquid two-phase flow in a horizontal pipe

A drift-flux correlation has been often used to predict void fraction of gas-liquid two-phase flow in a horizontal channel due to its simplicity and practicality. The drift-flux correlation includes two important drift-flux parameters, namely, the distribution parameter and void-fraction-weighted-mean drift velocity. In this study, an extensive literature survey for horizontal two-phase flow is conducted to establish void fraction database and to acquire existing drift-flux correlations. A total of 566 data is collected from 12 data sources and 4 flow-regime-dependent and 1 flow-regime-independent drift-flux correlations are identified. The predictive capability of the existing drift-flux correlations is assessed using the collected data. It is pointed out that the drift velocity determined by a regression analysis may include a significant error due to a compensation error between distribution parameter and drift velocity. In this study, a simple flow-regime-independent drift-flux correlation is developed. In the modeling approach, the void-fraction-weighted mean drift velocity is approximated to be 0 m/s, whereas the distribution parameter is given as a simple function of the ratio of non-dimensional superficial gas velocity to non-dimensional mixture volumetric flux. The newly developed correlation shows an excellent predictive capability of void fraction for horizontal two-phase flow. Mean absolute error (or bias), standard deviation (random error), mean relative deviation and mean absolute relative deviation of the correlation are 0.0487, 0.0985, 0.0758 and 0.206, respectively. The prediction accuracy of the correlation is similar to the correlation of Chexal et al. (1991), which was formulated based on the drift-flux parameters by means of many cascading constitutive relationships with numerous empirical parameters.     

Effect of pipe diameter on flow patterns for air-water flow in horizontal pipes

New results are presented on interfacial patterns observed for air and water flowing in horizontal 2.54 and 9.53 cm pipelines close to atmospheric conditions. This work differs from previous studies in that measurements of pressure fluctuations at two locations separated in the streamwise direction are used to detect slugs. The liquid flow needed to initiate slugs at low gas velocities is strongly affected by pipe diameter and appears to depend on a linear instability. At high gas velocities the transition is approximately independent of pipe diameter and is explained by a nonlinear mechanism associated with the coalescence of roll waves. The initiation of slugs in the annular flow regime is determined to occur at much lower liquid flows than had been reported by previous investigators. The transition from stratified to annular flow is different in smaller-diameter pipes than in larger pipes because wave wetting plays a more important role.     

An analysis of holdup in horizontal two-phase gas-liquid flow

The Butterworth form of correlation for holdup in two-phase gas-liquid flow is justified theoretically for certain conditions. In addition, a wide range of experimental data were used to show that holdup data may be broadly classified into three major groups based on the flow pattern, and different relationships were found to represent the data in each group. Thus for slug and plug flow, the holdup is given by the Armand type of equation; for stratified flow the holdup is given by the theoretical equations which are derived while annular flow data are satisfactorily represented by a semi-empirical correlation.     

Structure of thin liquid films in gas-liquid horizontal flow

The structure of the liquid film in horizontal annular flow is studied visually using the refractive index matching technique. The liquid film is found to contain significant amount of air bubbles, which are continuously entrained, broken up and released by the rolling motion within the film. A new conceptual picture of the gas-liquid interface is presented.     

Flow pattern transitions in vertical and upwardly inclined lines

Additional data has been obtained on flow pattern transitions during cocurrent gas-liquid flow in vertical and upwardly inclined lines. These data, together with those previously available in the literature, have enabled the development of improved dimensionless correlations for flow pattern boundaries. The individual boundary lines bave been combined into simple overall flow pattern maps.