ANALYSIS OF MIXED FORCED CONVECTION OF A NON-NEWTONIAN FLUID IN A THICK CHANNEL UNDER SINUSOIDAL THERMAL EXCITATION

This study investigates mixed forced convection heat transfer of a non-Newtonian power-law fluid flowing in a thick-walled rectangular channel subjected to a sinusoidal wall temperature with a non-zero mean value. Viscous dissipation is fully taken into account, whereas axial conduction in the fluid is neglected under the assumption of high Peclet numbers. An asymptotic analytical solution for the temperature field is developed, from which the local Nusselt number is obtained, while the average Nusselt number is computed numerically. The influence of the power-law index n, Brinkman number Br, Peclet number Pe, and wall thickness ratio on heat transfer and temperature distribution is systematically analyzed. The results show that decreasing n (shear-thinning behavior) increases the velocity, reduces the bulk temperature, and significantly enhances the average Nusselt number, especially at higher dimensionless frequencies of the imposed sinusoidal temperature. The originality of this work lies in the simultaneous consideration of non-Newtonian rheology, viscous dissipation and conjugate heat transfer in a thick channel under sinusoidal thermal excitation, providing useful guidelines for the design and optimization of systems involving polymers, lubrication, compact heat exchangers and biomedical flows.