Laminar flow and convective heat transfer of non-Newtonian fluids in doubly connected ducts

A hybrid numerical–analytical solution based on the Generalized Integral Transform Technique (GITT) is obtained for laminar heat and fluid flow of power-law non-Newtonian fluids inside doubly connected ducts. The mathematical formulation is constructed in the cylindrical coordinates system in such a way that the solid surfaces are described in terms of internal and external radii as functions of the angular coordinate, thus avoiding discontinuities in the boundary conditions. An annular doubly connected duct of arbitrary geometric configuration is considered for the analysis of the fully developed velocity field, as well as for the temperature field under thermally developing flow with boundary conditions of prescribed wall temperature. For illustration purposes, the case of eccentric annular ducts is more closely analyzed in order to demonstrate the ability of the GITT approach in dealing with such class of problems. Numerical results for the velocity field, the product of the Fanning friction factor-Reynolds number, temperature field and Nusselt numbers were produced for different values of the governing parameters, i.e., eccentricity, radii ratio and power-law indices. Such results were examined against previously reported ones, providing critical comparisons in order to illustrate the adequacy of the employed integral transform approach.