(302h) Turbulent Dissolution, Drag Reduction and Degradation of Pipe Wall-Injected Polyox

Turbulent dissolution, drag reduction and degradation of wall-injected Polyox P309 solutions was studied by simultaneous axial pressure profile and flow visualization measurements at Reynolds numbers from 15000 to 150000 in a transparent test pipe of ID 16 mm and L/D 430.  Friction factors for solvent, deionized water, adhered to the Prandtl-Karman law for fully-developed turbulent flow in smooth pipes.  The P309 Polyox, of MW ~ 13x10⁶ with N_bb ~ 0.87x10⁶ backbone chain links, was injected as a concentrated solution C_inj = ei 500 or 1000 wppm through 6 equi-spaced circumferential ports at friction-normalized injection velocities V_inj⁺ ~ 1 << pipeline mean velocity V⁺ ~ 25.  Downstream polymer concentrations C_line varied from 0.2 to 20 wppm, exhibiting eventual fractional drag reductions DR_line from 0.10 to the asymptotic maximum drag reduction MDR ~ 0.80 possible at the present Re.  Polymer dissolution into the flow was assessed from the initial increase in fractional drag reduction towards the eventual downstream DR_line, which provided a characteristic development distance (L/D)_dr and also from flash photography which provided a characteristic distance (L/D)_pv where red-dyed strands of the injected solution disappeared.  Finally, at the lowest C_line and highest Re, drag reduction was observed to increase, peak, and then decline with increasing downstream distance.  Since the peak drag reduction corresponded roughly to the disappearance of the red-dyed strands, that is, to full polymer dissolution, the subsequent downstream decline in drag reduction could be ascribed to polyox degradation and used to estimate its kinetics.