Laminar Natural Convection from Two Vertically Attached Horizontal Cylinders Immersed in Unconfined Power-Law Fluids

Natural convection have emerging potential applications in non-Newtonian fluids. The apparent viscosity of a Power-law fluid exhibits a measurable variation with shear rates. Thus, the coupled velocity and thermal fields are further accentuated in Power-law fluids. Owing to the pragmatic significance, free convection from two vertically attached cylinders has been investigated numerically to elucidate the shear-thinning and shear-thickening behavior of a Power-law fluid using a modified Power-law model. Average Nusselt number shows a positive dependence on both Grashof and Prandtl numbers, whereas it shows an adverse dependence on Power-law index. Overall, shear-thinning behavior enhances the convection whereas shear-thickening behavior impedes it with reference to the generalized Newtonian fluids. Two competing mechanisms determine the resulting heat transfer: decreasing driving force due to preheating of the fluid by the lower cylinder and the mixed convection contribution due to the flow induced by the lower cylinder. As a result, the heat transfer from the upper cylinder has been strongly influenced by the plumes from the lower cylinder. Owing to the interaction of plumes, the heat transfer was found to decrease for both the cylinders compared to that of a single cylinder.