LAMINAR HEAT-TRANSFER IN A RECTANGULAR DUCT WITH A NON-NEWTONIAN FLUID WITH TEMPERATURE-DEPENDENT VISCOSITY

The present study investigates the effect of the temperature-dependent and shear-thinning viscosity of a non-Newtonian fluid on the behavior of the laminar heat transfer and friction coefficients in a 2:1 rectangular duct. The H1 thermal boundary condition, corresponding to an axially-constant heat flux and a peripherally-constant temperature, was adopted for a top-wall-heated configuration. The present numerical results of local Nusselt numbers for a polyacrylamide (Separan AP-273) solution show 70-300% heat transfer enhancement over those of a constant-property fluid and give excellent agreement with recent experimental results. The heat transfer enhancement from the heated top wall is due to an increased velocity gradient near the wall, which is attributed to the combined effect of the temperature-dependent and shear-thinning viscosity. Two new correlations for the friction factor and the local Nusselt numbers in the 2:1 rectangular duct are proposed; these correlations cover both thermally-developing and thermally-fully-developed regions. This study also proposes the use of a temperature-dependent shear-thinning fluid in a rectangular duct in the design of a liquid cooling module for the computer industry.