(321i) Turbulent Drag Reduction, Flow Development, and Degradation of Polyox U310 Solutions in a Smooth Pipe | AIChE

(321i) Turbulent Drag Reduction, Flow Development, and Degradation of Polyox U310 Solutions in a Smooth Pipe


Attah, O., Massachusetts Institute of Technology
Gomes, R., Massachusetts Institute of Technology
Selvakumar, R., Massachusetts Institute of Technology
Mannarino, N., Massachusetts Institute of Technology
Turbulent drag reduction, flow development, and degradation of Polyox U310 solutions was studied by axial pressure profile measurements in a smooth, segmented, pipe with electro-polished bore of ID 4.58 mm and overall L/D 210. The test pipe assembly, of 7 identical segments, each of L/D 30 with a 0.38 mm ID pressure tap 2.4 L/D from its downstream end, was placed in a single-pass progressive cavity pump-driven flow system fed from a 200 liter tank that held premixed polymer solution. The U310 Polyox, MW ~10x106, was studied at concentrations C = 0.1 to 10 wppm in deionized water DW solvent.

At any fixed flowrate, individual friction factors for DW solvent were constant to within 1.2% for all tap pairs; and all DW friction factors adhered to the Prandtl-Karman law, 1/â??f = 4.0 log Reâ??f - 0.4, within ±0.2 1/â??f units for 500 < Reâ??f < 3000. Thus the present solvent flows were all fully-developed by the first tap pair 1&2 at mean L/D = 42, in accord with established entrance lengths of 25 â?? 40 L/D for Newtonian turbulent pipe flow.

Drag reduction by U310 solutions, described by flow enhancements aka â??slipâ? Sâ?? = (1/â??fp â?? 1/â??fn)Reâ??f , varied over almost the entire possible range 0 < Sâ?? < Sâ??mdr, from Sâ?? ~ 1 for C = 0.1 wppm at low Reâ??f ~ 500 in the polymeric regime to Sâ?? ~ 15 for C = 10 wppm at high Reâ??f ~ 2500, close to the maximum drag reduction asymptote, 1/â??f = 19.0 log Reâ??f - 32.4. Two distinct kinds of Sâ?? vs L/D behaviour, described by examples, were discerned:  (i) At low C and high Reâ??f, example C = 0.1 wppm and Reâ??f > 1000, Sâ?? was highest initially (L/D = 42) and decreased monotonically with increasing L/D to the end (L/D = 192), likely reflecting polymer degradation with increasing downstream distance, and yielding an apparent degradation rate constant kdeg ~ 4 1/s at wall shear stress Tw ~ 100 Pa. (ii) At high C and all Reâ??f, example C = 10 wppm and 500 < Reâ??f < 2500, Sâ?? was lowest initially (L/D = 42), increased with increasing L/D, and asymptotically attained a constant Sâ?? ~ Sâ??mdr for L/D > 132, which likely represents the entrance length required for fully developed turbulent flow at maximum drag reduction.