Study For The Characteristics Of Two-phase Slug Flows In Hilly Terrain Pipelines

Slug flow is one of the most typical and common patterns in air-oil-watermultiphase pipes flow, with the characteristics of intermittent appearance andun-regularization. This kind of intermittent makes holdup and pressure sharplyfluctuate in a pipe. This might make such equipments as oil pump in inlet andseparator of oil & gas in the exit of pipeline work under un-safe and un-steadyenvironment for long periods. With the development of the petroleum industry,pipelines become longer and longer. Hilly terrain pipeline is common. It isnecessary for us to study slug flow in it. An air-water test loop was established and adjusted gradually with a section ofslightly inclined pipeline. In order to measure the slug length and velocity, a set ofconductance probe and a high-speed computer-based data acquisition system aredesigned. The results shows that liquid-slug length conform to normal condition. Theliquid-slug length is longer in the upward section than that in the horizontalsection ahead, and then liquid-slug length decreases in downward section. Thelarger the inclined angle is, the greater the change extent of the liquid slug lengthis. In the same superficial liquid velocity, the liquid-slug average length decreasewith the increase of superficial air velocity by statistic. The relationship of theliquid slug velocity to the mixture velocity is obtained. It is found that liquid-slug frequency is independent of inclined angle ofpipeline. Slug flow happen due to the inlet effect. The liquid-slug frequencydecrease first and then increase by the increase of superficial air velocity. Theliquid-slug frequency increase by the increase of the superficial liquid velocity.The relationship between the liquid-slug frequency and the superficial liquidvelocity is obtained. The two-fluid model was adopted to calculate the pressure loss on an air-water two-phase flow. The result shows that model is good agreement with withexperimental result. In the model presented here the pressure gradient is given bythe sum of four terms, including the hydrostatic head loss in an inclined pipe, - â…¡ -Abstractfriction pressure loss caused by wall shear stress, viscous loss associated with theeddy motion in the mixing vortex, and the accelerational pressure loss due to gasexpansion. In all cases the largest contribution to the pressure drop was thefrictional loss within the slug. However, the additional viscous and accelerationalcomponents were also significant. The accelerational term typically accounts forup to 5% and the viscous loss accounts for up to 2% of the total pressure loss.