화학공학소재연구정보센터
Journal of Non-Newtonian Fluid Mechanics, Vol.104, No.1, 33-51, 2002
Birefringent strands in polymer flows in a co-rotating two-roll mill
Flow of a polymer solution in a co-rotating two-roll mill is studied as the speed of one of the rolls is varied. Optical experiments using aqueous solutions of PEO verify the presence of a "birefringent strand", caused by the elongation and alignment of polymer molecules downstream of a stagnation point in the nip. Measurements of its position and its parametric dependence on K, the ratio of roll speeds, are presented. A strand theory, in which the elastic stresses created by the polymer are approximated by a line discontinuity in shear-stress, is used to form governing differential equations for the strand velocity and position and the pressure gradient. Integration of the equations yields profiles of the strand position and velocity for given parameters K and lambda, a non-Newtonian parameter dependent on material properties of the polymer. Numerical results for the symmetric case (K = 1.0) compare well with previously published results; a best-fit to the corresponding experiment yields a value of lambda approximate to 10, which compares well with estimated values of apparent extensional viscosity and direct measurement of the strand thickness. The numerical solutions for K < 1.0 compare qualitatively but not quantitatively with the experimental strand profiles. The discrepancy is consistent with an approximate treatment of the shear-thinning behavior present in the experiments.