EXPERIMENTAL AND NUMERICAL STUDY OF FRICTION FACTOR FOR A MODIFIED POWER-LAW FLUID IN A RECTANGULAR DUCT

Numerical solutions are presented for fully developed laminar flow for a modified power law fluid (MPL) in a rectangular duct. The solutions are applicable to pseudoplastic fluids over a wide shear rate range f rom Newtonian behavior at low shear rates, through a transition region , to power law behavior at higher shear rates. The analysis identified a dimensionless shear rate parameter that for a given set of operatin g conditions specifies where in the shear rate range a particular syst em is operating, that is, in the Newtonian, transition, or power law r egions. The numerical results of the friction factor times Reynolds nu mber for the Newtonian and power law region are compared with previous ly published results showing agreement within 0.05% in the Newtonian r egion and 0.9 and 5.1% in the power law region, respectively. Rheologi cal flow curves were measured for three CMC-7H4 solutions and were fou nd to be well represented by the MPL constitutive equation. The fricti on factor times Reynolds number values were measured in the transition region for which previous measurements were unavailable. Good agreeme nt was found between experiment and calculation, thus confirming the v alidity of the analysis.