Neima Brauner

Holdup of the liquid slug in two phase intermittent flow

Abstract A physical model for the prediction of gas holdup in liquid slugs in horizontal and vertical two phase pipe slug flow is presented. This model can also be used to yield the transition between elonganted bubbles and slug flow within the intermittent flow pattern. In addition a previously published model for predicting the stable slug length in vertical upward slug flow (Taitel et al. 1980) is extended here for the case of horizontal slug flow.

Identification of the range of ‘small diameters’ conduits, regarding two-phase flow pattern transitions

Abstract Integrated frame of both stability and well-posedness analyses is shown to predict the complete stratified/nonstratified transitional boundary over wide ranges of conduit size. It is shown that the stabilizing effects of surface tension associated with practically finite wave lengths must be considered. This explains the basic defficiency of all previous analyses which employed single stability criteria of infinite long waves. The range of ‘small diameters’ conduits, regarding flow pattern transition, is identified by Eotwos number smaller than unity.

Flow pattern transitions in two-phase liquid-liquid flow in horizontal tubes

Abstract As the various concepts and results experienced in gas-liquid two-phase flows cannot readily be translated to liquid-liquid systems, an attempt is made to form a basis for constructing a general two-fluid flow pattern map. The departure from a steady stratified configuration to other bounding flow patterns is analysed in view of the relationships between the instability criterion and the conditions for reality of characteristics, which evolve from exploring the stability and well-posedness of the governing equations. The transitional boundaries between the other flow patterns encountered in liquid-liquid systems are obtained based on mechanistic models. A parametric study made for wide ranges of geometry and physical properties, as encountered in liquid-liquid systems, is also included. Comparisons of the proposed transitional criteria with (limited) available data in liquid-liquid systems show reasonable agreement. The convergence of the general criteria to the extremes of gas-liquid data, on the one hand, and the data of highly viscous core flows, on the other hand, is satisfactory.

Stability analysis of stratfied liquid-liquid flow

Abstract Linear stability analysis is being widely used in exploring gas-liquid stratified/non-stratified transitions. As the present study relates to liquid-liquid two-phase systems, the stability characteristics of stratified layers are considered. In parallel, the conditions necessary for real characteristics are also explored. The relations between stability conditions and those for well-posedness are discussed in view of the implications for flow pattern transitions. The convergence of the stability conditions to various extremes is discussed. The integrated considerations of stability and well-posedness shed light on the physical sequences in flow pattern transitions, which so far have been studied by stability analysis alone. As liquid-liquid systems are involved, wide ranges of density and viscosity ratios are studied for various operational conditions.

Modeling of phase inversion phenomenon in two-phase pipe flows

Abstract Phase inversion in oil–water flow systems corresponds to the transitional boundary between oil-in-water dispersion and water-in-oil dispersion. In this study, the criterion of minimum of the system free energy is combined with a model for drop size in dense dispersions to predict the critical conditions for phase inversion. The model has been favorably compared with available data on the critical holdup for phase inversion. It also provides explanations of features of phase inversion phenomena in liquid–liquid pipe flows and in static mixers.

Characteristics of inclined thin films, waviness and the associated mass transfer

Abstract The relationship between the undulatory nature of inclined thin film flows and the transfer characteristics have been demonstrated and qualitatively established. This provides a basis for future analytical treatments of the hydrodynamics of wavy flows and their influence on the transport phenomena. The boundary between the smooth film entry region and the wavy region has been discussed with relation to various operation conditions. The waviness characteristics at the rippled region and their development have been broadly studied and discussed.

A physical model for predicting the minimum stable slug length

Abstract A physical model for the prediction of the minimum stable slug length in vertical and horizontal slug flows is presented. The model is based on a new concept of recurrent relaxation of the wall boundary-layer at the slug front and its redevelopment at the slug back. Due to the overlapping process in the developing region the probable average stable slug lengths should range between the predicted minimum stable slug length and twice this value. Comparisons with experimental data is satisfactory. The prediction of the slug length provides an improved method to effect closure for previously existing models for this flow pattern.

Slug/Churn transition in upward gas-liquid flow

Abstract A new predictive model for slug/churn transition is presented. It is suggested that the transition takes place when the gas void fraction within the liquid slug reaches the bubble maximum volumetric packing. The predicted boundary is compared with experimental results and shows satisfactory agreement. The model is extended to inclined pipes, and provides a quantitative explanation for the shrinkage and vanishing of the churn pattern in inclined pipes.

A two-fluid model for stratified flows with curved interfaces

Abstract This study is motivated by the need to develop a practical tool for predicting the interface shape in stratified flow of a general two-fluid system. A configuration of a curved interface is considered. A two-fluid model is used to solve the momentum equations for a variable interface curvature. Energy considerations provide a closure relation for the interface curvature. The analysis identifies all the input dimensionless parameters which determine the solution for the stratified flow pattern. When these are given, a complete solution of the problem is obtained, including the interface shape, in situ hold-up and pressure drop. The validity of the two-fluid model is evaluated by comparing its prediction with available experimental data and with the results of exact analytical solutions for laminar flows with curved interfaces. Thus, the conventional two-fluid model has been extended to tackle stratified flow with curved interfaces and various flow regimes, in which case analytical solutions are complicated and restricted to laminar flows.

Two-phase liquid-liquid annular flow

Abstract A simple predictive tool for analyzing the annular-core flow of two immiscible liquids is presented. The model puts under a common framework all possible flow situations of laminar-laminar, turbulent-turbulent or mixed flow regimes in the two phases involved for wide ranges of viscosity and density ratios. Comparison with available experimental data of pressure drop and in situ hold-up shows a satisfactory agreement. The potential of the core flow configuration for achieving pressure loss reduction and power saving in the transportation of very viscous oils is evaluated, addressing the problem of tube size scale-up.