Effectiveness of Polyisobutylene as Drag Reducing Agent in Turbulent Pipe Flow

Izzat Niazi Slaiman
Prof. Dr. Jabir Shanshool

 Drag-reduction by the use of minor amount of polymeric additives is by far the most technique to reduce the frictional resistance and to save pumping power for turbulent pipe flow. In the present work, the turbulent drag-reduction effectiveness of polyisobutylene, type oppanol B 250 was studied in a build-up closed loop circulation system at different flowing conditions.The turbulent mode was produced via a positive displacement pump to avoid any shear degradation of polymer chains during the pumping stage. Drag-reduction results were assessed by measuring pressure drop over two test sections from the pipes.The effect of additives concentration was investigated over a range up to 50wppm in flowing gas oil, at flow rates 2.8 to 6.0m3/hr in four pipes of 19.05 to 50.80 mm I.D pipe. Moreover, the effect of kerosene solvent type was also studied in 31.75 mm I.D pipe for comparison purposes. A gradual increase of percentage drag-reduction was observed with increasing the polymer concentration and bulk velocity. The 31.75 mm pipeline shows higher drag-reduction compared to smaller pipe with 19.05 mm I.D pipe at given velocity. The drag-reduction in kerosene was slightly higher than that in gas oil due to the difference in their viscosities. The 50wppm polymer treated gas oil shows the greatest degree of calculated, fanning friction factor reduction,approaching the maximum drag-reduction, at higher flow rates in a 31.75 mm I.D pipe. A simple fitting was used to predict the friction factor as a function of Reynolds number. The results show good agreement with the corresponding data obtained on experimental bases. The drag-reduction results have been correlated based on modification of a theoretical model which requires knowledge of the wall shear rate, pressure drop and additive concentration. The results of the correlation showed acceptable agreement between the observed and predicted dragreduction values.The time dependence of drag-reduction effectiveness was studied in order to investigate the possible  molecular degradation of polymer additives during the circulation of solution.The experiments were carried out by using polyisobutylene with,three different molecular weights,type’s oppanol B  150,200 at concentration 50wppm and B
250 at different concentrations up to 50wppm.  It was found that the lower molecular weight polymers lost their activity faster than higher molecular weight B 250 type. Moreover, the rate of degradation is strongly dependent on pipe diameter. The time dependence degradation behavior of the three mentioned  polymers in turbulent flow was also analyzed by modifying the fractional exponential decay equation. The modified equation was found to fit the experimental data of the three polymer types better than the original equation.