  The velocity and friction properties of laminar pipe flow of a viscoelastic
solution are bounded by the corresponding values for two Newtonian fluids,
namely, the solvent and a fluid with a viscosity identical to the total
viscosity of the solution. The lower friction factor for the flow of the
solution when compared to the latter is tracked to an increased strain rate
needed to enhance viscous dissipation. Lastly, we show analytically that the
effective viscosity varies similarly to the radial diagonal component of the
conformation tensor as observed numerically in turbulent flows, and give a
lucid interpretation of shear-thinning through a sequence of underlying
constitutive physical phenomena.
