POLYFLOW  evaluation of a typical wall shear rate
Considering a flow rate Q, and some geometric dimensions (width L, half height H, radius R), what is a typical wall shear rate gdot? The formulae below provide typical values; they assume that the geometry is smooth and that the viscosity is constant. For shearthinning materials, the actual wall shear rates can be some 50% larger. 2D planar flow (between two plates):  the flow rate Q is given per transverse unit of length [thus e.g. cm^3/s/cm]  the channel has a height 2H  the typical wall shear rate is given by gdot = 3.Q/(2.H^2) 2D axisymmetric flow (through a circular tube):  the flow rate concerns the whole circular cross section  the cross section has a radius R  the typical wall shear rate is given by gdot = 4.Q/(pi.R^3) 2D axisymmetric flow (through an annular tube):  the flow rate concerns the whole annular cross section  the cross section has an average radius R and an opening 2e  the typical wall shear rate is given by gdot = 3.Q/(4.pi.R.e^2) or Q/(4.R.e^2) 3D flow:  the flow rate concerns the actual cross section  the cross section has a length L and a width 2H (with H < L)  the typical wall shear rate is given by gdot = 3.Q/(2.L.H^2)  for an annular cross section, the actual geometry can be unrolled. 

