EFFECTS OF SHEAR THINNING ON LAMINAR HEAT-TRANSFER BEHAVIOR IN A RECTANGULAR DUCT

The fluid dynamic and heat transfer behavior of laminar non-Newtonian flow through noncircular ducts is of special interest because of their wide range of potential application to compact heat exchangers and in electronics cooling. The present study investigates the heat transfer characteristics for laminar forced convection of inelastic non-Newtonian fluids in a nonuniformly heated rectangular duct where the flow is hydrodynamically developed but thermally developing. The governing equations are solved by a finite volume method. Second-order accurate differencing schemes are employed for both the diffusion and convective terms. The effects of shear thinning, given by the Carreau equation, and the viscous dissipation, characterized by the Brinkman number, are examined via the friction factor, the Nusselt number, and the bulk fluid temperature. The results indicate that when viscous dissipation is present, the heat transfer from the heated surface of the duct is greatly enhanced with increased shear thinning of the fluid while the rate of increase of the bulk fluid temperature with axial distance will significantly decrease. Consequently, the use of a shear-thinning non-Newtonian fluid for heat transfer enhancement appears to be a very promising concept that is worthy of further study.