HEAT-TRANSFER MECHANISM FOR NEWTONIAN AND NON-NEWTONIAN FLUIDS IN 2 1RECTANGULAR DUCTS/

A numerical study has been performed on the heat transfer mechanism of Newtonian and non-Newtonian fluids in 2: 1 horizontal rectangular duc ts. The effects of temperature dependence of viscosity, shear thinning , and buoyancy-induced secondary flow are all considered. Experimental data for Newtonian fluid, water, and non-Newtonian fluid, Separan AP- 273 solution (0.1%), were chosen for the comparison with the numerical results. For water, the present numerical results are all in good agr eement with the experimental data. The heat transfer enhancement is ca used by the buoyancy-induced secondary flow. For Separan AP-273 soluti on (0.1%), the present numerical results agree with the experimental d ata in the region near the entrance, but the present modeling underest imates the value of Nu in the fully-developed region. In the region ne ar the entrance, the heat transfer enhancement is caused mainly by the axial velocity distortion, which is mainly due to the temperature dep endence of viscosity. The effect of buoyancy-induced secondary flow ar e much weaker in the case for Separan solution rather than that for wa ter. It is mainly caused by the relatively high viscosity of fluid aro und the central zone of rectangular duct. (C) 1998 Elsevier Science Lt d. All rights reserved.