STUDY OF DRAG REDUCTION IN TURBULENT FLOW USING HIGH MOLECULAR WEIGHT POLYMERS

Drag reduction has been studied in a build-up closed loop water circulation system using two different types of polymers namely: carboxy methylcellulose CMC and Xanthan Gum, XG of molecular weight 0.4*106and 5.0*106g/mol respectively.The turbulent mode was produced via a positive displacement gear pump to avoid mechanical degradation of polymer chain during the experimented period. The  effect of polymer concentration was investigated over a range of (up to 300 ppm)at different flow rates up to 6 m3/h and Reynolds number grater than 33418.71 in a flow pipe diameter 1.25 inches. A gradual increase of drag reduction was achieved by increasing the polymer concentration and water flow rate. The drag reduction effectiveness of the lower molecular weight CMC additive is lower than for XG of higher molecular weight. The maximum percentage drag reduction values were achieved experimentally at 300 ppm polymer concentration and 6.0 m/h flow rate. Those are 16% and 23.3% for CMC and XG,respectively. The drag reduction performance for mixtures of the two polymers, CMC and XG was also studied during this work. The results show that it is possible to enhance the drag reduction effectiveness of CMC additive by mixing it with XG of high molecular weight.Part of the experimental work was devoted to study the performance of CMC and XG solutions as drag reducers with the existence of small amounts of sodium chloride to reduce the drag forces. The results show that sodium chloride acts as an inhibitor to the effectiveness of such additives, resulting in lower percentage drag reduction values. This could be attributed to the fact that CMC and XG additives as polyelectrolyte molecules collapse at more compact structure with the addition of sodium chloride as strong ionic salt.The time dependence of drag reduction effectiveness undergoes molecular shear degradation during turbulent flow. Thus, the percentage drag reduction reduces rapidly during the early stages of circulation for both additives. The degradation is more likely to occur at low concentration.A simple correlation equation was suggested to predict the effect of flow parameters, additive molecular weight and concentration, flow rate and finally sodium chloride molecular weight and concentration on percentage drag reduction. The results of the correlation showed satisfactory agreement between observed and predicted values with about 96% correlation coefficient for both CMC and XG additives