Rheological properties of polymer melts are often described with a lin
ear model, the two-parameter power-law model in industrial application
s, while the real polymer melts behave more or less nonlinearly, parti
cularly in the low shear rate regions. In a lot of real flows, such as
the simple pipe now, there is even a zero shear rate region. Therefor
e, the adequacy of this linear approximation has to be examined, in th
is paper, the polymer melt flow in a pipe is studied using the nonline
ar three-parameter Powell model. Numerical results are presented in se
veral graphs, which can be used in engineering calculations. A compari
son with the test data has been given. The restrictions of using the p
ower-law model and the impact in handling the experimental data are di
scussed.