Laminar heat transfer to viscous non-Newtonian fluids in non-circular ducts

A computational and experimental study was made of the steady developing laminar convective heat transfer to viscous non-Newtonian fluids described by the power law model flowing in straight channels of circular and several non-circular cross-sections. In the numerical study the governing conservation equations in three dimensions subject to suitable boundary conditions were solved after appropriate discretization, using the Galerkin finite element method. Fourteen different cross-sectional geometries were studied numerically. Effects of temperature-dependent apparent viscosity, viscous dissipation as well as Prandtl number were included in the model. The thermal boundary conditions tested were: uniform wall temperature and uniform wall heat flux on the entire duct surface. Predicted velocity fields, pressure drop, and heat transfer distributions were compared with available data and simulation results as appropriate. Results are presented on the comparative thermal performance of various cross-sectional ducts.In the experimental study the critical Reynolds numbers were measured for distilled water flowing through a semi-circular and an equilateral triangular duct. Local Nusselt number distributions are presented for ducts with the horizontal bottom plane sides subjected to uniform heat flux while the rest of the channel is well insulated. The measured pressure drop and Nusselt number distribution for Carbopol solutions compared very well with the numerical predictions