Paper
Flexible polymers exhibit pronounced drag reduction but weak resistance to mechanical shear, whereas rigid polymers exhibit remarkable resistance to mechanical shear but slightly weaker drag reduction. Therefore, mixing flexible and rigid polymers could offer improvements in comprehensive drag-reduction performance. This letter reports an experimental study on the drag-reduction performance of binary polyacrylamide (PAM) and xanthan gum (XG) solutions with the PAM concentration fixed at 10 ppm. From comparing curves of the drag reduction rate vs Reynolds number and shearing time, 70-ppm XG is the optimal choice for forming a binary polymer solution with 10-ppm PAM. This binary solution also offers drag-reduction effects equivalent to those of a pure 50-ppm PAM solution. Although it decreases with time, the synergistic coefficient still remains much larger than zero. This implies that the positive synergistic effect of the PAM–XG binary solution persists even under long-term shearing. These results offer a fundamental basis for developing high-performance polymer drag reducers.