Natural Convection in Power-Law Fluids from a Pair of Two Attached Horizontal Cylinders

Abstract

Laminar natural convection in unconfined power-law fluids from two attached horizontal cylinders has been investigated numerically to elucidate the non-Newtonian behavior of the fluid over a wide range of pertinent parameters: Grashof number (10 to 105), Prandtl number (0.71 to 100), and power-law index (0.2 to1.8). The heat transfer characteristics are elucidated in terms of isotherms, local Nusselt number distributions, and average Nusselt number values, whereas the flow characteristics are interpreted in terms of streamlines, local distribution of the pressure drag, and skin friction drag coefficients along with the total drag coefficient values. Under identical conditions, the average Nusselt number shows a positive dependence on both Grashof and Prandtl number, whereas it shows an adverse dependence on power-law index. Overall, shear-thickening fluid behavior impedes the convection heat transfer, whereas shear-thinning fluid behavior promotes it with reference to the Newtonian fluids. The heat transfer from an individual cylinder in attached condition has been degraded compared to the case of a single horizontal cylinder. Furthermore, the heat transfer rate of the top cylinder is reduced by 29%–41% relative to that of the bottom cylinder due to preheating of the thermal plume.