Modeling the effects of oil viscosity and pipe inclination on flow characteristics and drag reduction in slug flow

Computational analysis along with extensive experimental investigation have been carried out to predict drag reduction in slug flow utilizing three types of oil with viscosities of 2.5 cP, 26 cP, and 50 cP in 10-cm ID, horizontal and 2-degree inclined pipes. Effects of oil viscosity and pipe inclination on each component of the total pressure drop in slug flow were determined. The impact of liquid viscosity and pipe inclination on the effectiveness of drag reducing agents (DRA) was also investigated. Predicted values were in good agreement with experimental results.; Results from both experiments and modeling showed that the accelerational component of pressure drop was dominant in low and moderate oil viscosities. This component reached values as high as 86% of total pressure drop. Most of the drag reduction took place in the accelerational component and reached values as high as 88% out of total drag reduction. As oil viscosity increased, the frictional component was found to increase dramatically and exceeded 40% of total pressure drop in the 50 cP oil.; The DRA was found more effective in reducing both frictional and gravitational components of total pressure drop in higher-viscosity oils than in lower ones. For example, at superficial liquid and gas velocities of 0.5 and 6 m/s frictional loss was reduced by a factor of 60% in the 26 cP oil when adding 50 ppm of the DRA. The corresponding value for the 2.5 cP oil was less than 10%. Meanwhile, the DRA was more effective in reducing accelerational component, hence total pressure drop, in the 2.5 cP oil than in the 26 cP oil.; Pressure drop increased significantly when pipe inclination was changed from horizontal to 2 degrees due to the presence of the gravitational component. This increase in pipe inclination was accompanied with a decrease in the velocity of the stratified film ahead of each slug. Thus resulting in an elevated accelerational pressure loss.; This work will help introduce new mechanisms for drag reduction in multiphase flow and provide a new mechanistic or empirical correlation to incorporate drag reduction in multiphase flow.