【正文】 the way for subsequent research in the area, 本科畢業(yè)設(shè)計（論文）外文翻譯 5 and most of their transition criteria are still in use in more recent twophase flow models. Few years after that initial work, Taitel and coworkers extended the model for the vertical and near vertical case and Barnea extended the phenomenological approach to the whole range of pipe inclinations in the 1980s. These three works are monly referenced among researchers in the area, with a number of attempts at improvement. Additional steadystate prehensive mechanistic models for two phase flow in vertical wells, horizontal pipes and deviated wells were presented by Ansari, Xiao, Kaya and coworkers in the 1990s. All these mechanistic models were developed at the Tulsa University Fluid Flow Projects and are usually referred to as TUFFP models. Nowadays, there are also a number of mercially available two phase flow packages, which include various features intended to acplish specific tasks. Examples include OLGA, TACITE, PEPITE and PIPESIM, among others. Modern multiphase flow analysis models the flow of oil and gas through pipelines by invoking the basic principles of continuum mechanics and thermodynamics. Depending on how these equations are applied and how the interactions between phases are described, the most widely used twophase models are the homogeneous model (flow treated as a single phase with averaged fluid properties), driftflux model (flow described in terms of an averaged local velocity difference between the phases), separated model (phases considered to be flowing in separated zones of the channel) and twofluid model (a multifluid model that considers two flowing phases and their interactions). In the last decade, a great deal of attention has also been devoted to mechanistic or ‘phenomenological’ models – . models trying to capture specific features of individual flow patterns – in which simplified conservation 本科畢業(yè)設(shè)計（論文）外文翻譯 6 equations are invoked while the main focus is the prediction of pressure drop and holdup. However, in previous decades, the challenge of modelling twophase flows by invoking such fundamental laws had been circumvented by reliance on empirical and semiempirical correlations, especially in the oil industry. Perhaps one of the most fundamental and rigorous approaches to the study of largescale multiphase flow currently in use in the petroleum industry is the twofluid model. In the twofluid model, separate conservation equations (mass, momentum and energy) are written for each of the two phases for a total of six equations. These equations are coupled with terms describing the interaction between phases. In this twophase flow method of analysis, as well as in all the others, empiricism cannot be pletely avoided, since additional closure relationships are needed. Empiricism es into the picture during attempts to model the variety of constitutive relationships that show up in conservation equations. For instance, Ayala et have presented a unified twofluid model for the analysis of natural gas flow in pipeline in multiphase flow regimes. Their formulation assumes that both gas and its condensate are a continuum and invokes the basic laws of continuum mechanics in one dimension coupled with a thermodynamic phase behavior model. In their work, the required semiempirical relationships needed to give mathematical closure to the model are discussed in detail. Smallscale Interest and Computational Physics The study of smallscale multiphase flow has proved to be extremely difficult for researchers due to the elusive nature of the phenomena and the inherent limitations of experimental setups. A great deal of progress has been made on the development of useful smallscale experimental studies, but numerical experiments or models still remain the most effective way of studying 本科畢業(yè)設(shè)計（論文）外文翻譯 7 such detailed flow behaviour. The challenge of modelling smallscale multiphase flow resides in the finite nature of the puter power typically available to the modeller and the difficulty of tracking separated phases (and interfaces between them) with sharply different properties. The interplay of these two factors has historically limited the plexity of the systems that can be studied using smallscale simulation. However, during the last decade, major progress has been achieved by implementing a variety of numerical techniques, which typically depend upon the flow pattern type that prevails under the conditions of the study. The study of smallscale phenomena started when a group of scientists at the Los Alamos National Laboratory began to develop the basis of Computational Fluid Dynamics (CFD) in the early and mid1960s. In multiphase flow modelling within smallscale interest, the NavierStokes equations – with the appropriate boundary conditions – are solved through a suitable numerical method – . finite volumes, finite differences, finite elements or spectral methods. The main problem arises when considering that some boundary conditions are timedependent, since they are located at phase boundaries, which are free to move, deform, break up or coalesce. Different methods have been proposed。 here we mention a few of them. The most mon small