Gas flow regimes pdf

It has been possible to correlate the variations of NUT with the corrected pressure drop for one and several elementary cells. Experimental data show that the additivity of the performances of the cells is not satisfied because of the hydrodynamics phenomenum of liquid entrainment priming.

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Bookmarking Mendeley. This is the velocity the liquid would have in the pipeline, if only the liquid phase was present. Likewise, the superficial gas velocity is the velocity the gas would have, if only the gas phase was present.

Pipeline Profile Changes in elevation of the pipeline route play an important role in two-phase flow pipeline design and operation. The elevation profile, which represents the angle of inclination in every point of a pipeline, influences the liquid hold-up and determines the flow regime.

This in turn impacts the pressure loss incurred during the two-phase flow.

Liquid Hold-up Liquid hold-up is the accumulation of liquid in the pipeline because of the difference in velocity slip between the phases and the influence of gravity See Figure 3. Liquid holdup is usually larger than the liquid volume fraction. The only exception might be during a downward sloping flow at low velocity. Two-phase Flow Regimes The way in which liquid and gas simultaneously flow within a pipeline is characterized by what is known as flow regimes.

Flow regimes indicate the distribution of the phases over the cross sectional area of the pipeline. Many investigators, including a special institute at the University of Tulsa, have extensively analyzed two-phase flow patterns and regimes.

Some of the most commonly occurring two phase flow regimes in pipeline are: Bubble flow Annular dispersed flow Stratified or laminar flow Plug or churn flow Slug flow The relative positions of the liquid and gas as they move along the pipeline depend on whether the flow is horizontal or vertical.

Figure 4. Figure 6 exhibits a flow pattern map, which shows how flow behavior depends on the gas and liquid loading. Bubble flow In this type of flow, bubbles of gas flow along with the liquid at about the same velocity.

Flow Regimes

In horizontal pipelines gas bubbles move along the upper part of the pipe. Annular dispersed flow In this flow regime, the liquid flows along the wall of the pipe, while the gas flows at high velocity in the center of the pipe.

Stratified flow In stratified flow both gas and liquid flow separately with a distinct and relatively smooth interface between them. Gas flows in the upper part and liquid moves in the lower part of the pipe. Sometimes a wave is formed; it is then called stratified wavy flow. Plug or Churn flow This is similar to bubble flow, except that the gas bubbles coalesce into large bubbles or plugs.

In horizontal flow the plugs flow on the upper part of the pipe, while, in vertical flow, they tend to flow in the center of the pipe.

Slug flow Slug flow is similar to stratified wavy flow, except that the top of some waves touches the pipe wall and the flow tend to be alternative slugs of liquid and gas. In vertical flow, alternative slugs of liquid flow in the center of the pipe along with gas.

Two-phase Flow Pipeline Pressure Loss The pressure drop in a pipeline for two-phase flow is higher than that of single-phase flow. The increased pressure loss is essentially caused by the additional friction loss due to the formation of waves and slugs. A number of different correlation's have been developed by different authors to predict pressure loss in a pipeline for two-phase flow.

Some are more suitable than others for specific fluid types, giving varying levels of uncertainty. Usually companies develop their own correlation's for two-phase flow that can be generally applied. The behavior of a two-phase pipeline is normally evaluated using specialized process simulation computer packages.

The simulation package will take the input parameters and use two-phase flow equations and correlation's to determine the flow regimes, pressure loss and liquid hold-up for the pipeline. The graph in Figure 7 shows the required pipeline inlet pressure to achieve a fixed outlet pressure for a range of throughputs and pipeline diameters. This is a typical output and is invaluable in determining the optimum pipeline diameter. Two-phase Liquid Hold-up When designing a two-phase pipeline system, usually, a graph is generated showing how liquid hold-up volume varies with throughput and with varying pipeline diameters See Figure 8.

This is an invaluable piece of information. In a two-phase pipeline, one must first predict the amount of liquid expected to be present and then manage it. An understanding of how the anticipated liquid hold-up in a pipeline will vary with flow-rates will greatly help in formulating a suitable liquid management system.

This could perhaps include slug-catcher, pigging facilities or operational limits on ramp-up times. Two-Phase Applications Although it is more challenging to design and operate two-phase flow pipelines, they have been successfully built and operated throughout the world.

It used to be that in typical operations, two separate lines would automatically be built for gas and oil, transporting from the same source and often delivering to the same delivery point. However, where, construction costs are high, such as offshore, building a single two-phase pipeline rather than two separate lines is often the most economical approach.

Figure 9 illustrates an example of a two-phase pipeline system built offshore Denmark. This very large production system handles many fluid combinations. To be able to operate such a complex transport system one must be able to accurately predict and manage the pipelines. En savoir plus à propos de l'abonnement Scribd Bestsellers. Bien plus que des documents. Commencez l'essai gratuit Annulez à tout moment.

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Gas flow regimes pdf

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