Effect of Molecular Weight on Turbulent Drag Reduction with Polyisobutylene Additives

 Turbulent drag-reduction efficiency of polyisobutylene with three different, very high molecular weights was studied in a build-up closed loop gas oil circulation system. The turbulent mode was produced via a positive displacement gear pump to avoid mechanical degradation of polymer chains during the experimental period. Three molecular weights 2.9*10⁶ ,5.9*10⁶ g/mol dissolved in reformate were used as additives in order to investigate the effect of molecular weight on drag-reduction rate and flow capacity increase. The effect of polymer concentration was investigated over a range up to 70 wppm. The gas oil flow conditions that were studied included Reynolds number 8341 to 17874 as well as inside pipe diameters 1.0, 1.25 and 2.0 inches. A gradual increase of drag reduction and throughput was achieved by
increasing the polymer concentration and gas oil flow rate and decreasing the pipe diameter  Friction factor was calculated from the experimental data. For untreated gas oil pipelining, friction factor values lies near Blasuis asymptotes. While by addition of polymer drag reducer into the flow, the friction factor values were positioned towards Virk maximum drag-reduction asymptotes,noticeably for the highest molecular weight type. Furthermore the investigation showed that the degree of molecular weight is significantly in drag reduction performance. Correlation equations were suggested to predict the effect of flow parameters, concentration, flow rate, pipe diameter and finally polymer molecular weight on pressure drop reduction. The results of the correlations showed good agreement between the observed and predicted pressure drop
reduction values, with a higher than 99.5 %. The presented data should be useful in possible field applications, in order to increase the flow capacity for crude oil and fractions transportation pipelines system, specially by use the 5.9*10 ⁶ molecular weight polyisobutylene additive.