where Nu is the Nusselt number (Nu=hD/k dimensionless),
k is the thermal conductivity (W/m K), n is the flow
behaviour index (dimensionless), Gz is the Graetz number
(ρqCP/kL = π/4(Re Pr(d/L)) dimensionless), μ is the average
apparent viscosity (Pa s) and μw is the apparent viscosity at
the wall temperature (Pa s). This correlation presents values that
are different from those found in literature, particularly for the
dependence of the heat transfer coefficient on the viscosity.