The effect of surface activeagents on friction reduction in pipe liquid flow

Rana Zuhair Mohammed
Prof. Dr. Jabir Shanshool

The turbulent drag-reduction effectiveness of two anionicsurfactants, Sodium Dodecy -Benzene Sulfonate (SDBS) and Sodium laureth sulfate (SLES) has been studied in a build up closed loop water circulation system, the turbulent mode wasproduced via a positive displacement gear pump to avoidmechanical degradation surfactant molecules during theexperimental period. Drag- reduction results were assessed bymeasuring the pressure drop over 2m test section. The effect ofadditive concentration was investigated over a range of 50 to250ppm by weight in flowing tap-water at flow rates of 2.0 to 6.0 m 3 /hr in a 0.0508 m(2 inch) pipe diameter. A gradualincrease of percentage drag - reduction and flow capacity(throughput) was achieved by increasing the detergentconcentration and water flow rate, reaching up to 38.36% dragreduction and 30.49% throughput increase. The SDBS detergentgave high drag -reduction values and therefore it's more effectivethan SLES detergent at the optimum condition. The effectivenessof these anionic surfactants could be attributed to the shearstability of micelles structure as a result of rod shaped micellesforming.In order to investigate the performance of the anionic surfactants as drag reducers in the flowing saline water, the screening studies were carried out in presence of small amountsof sodium chloride or calcium chloride. A gradual decline ofdetergent effectiveness was noticed by increasing the saltconcentration in water. This observation my be due to less shearstability of micelles structure as a result of presence of suchstrong ionic salts. Calcium chloride caused higher inhibition of drag reduction effectiveness by the detergents than sodiumchloride. Since, calcium chloride forms with the anionicdetergent insoluble salts leading to deactivate such drag reducers. Friction factor was calculated from experimental dataobserved at different flowing conditions. For untreated waterpipelining friction factors values lies near Blasius asymptotes.While, the increasing the detergent concentrations at highReynolds number causes  decreasing the friction factor valuestoward Virk asymptote line, which was never reached. The presence of sodium chloride and calcium chloride is small amounts result in values positioned toward Blasius asymptote indicating the less effectiveness detergent additives as drag reducers. A simple correlation equation was suggested to predict the effect of flow parameters, detergent molecular weight and concentration, water flow rate and salt concentration on drag reduction effectiveness of anionic detergents. The results of correlation showed good agreement between the experimentally observed and predicted percentage drag reduction values wit higher than 94.758%.                                                                    

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