Effect of Horizontal Spacing on Natural Convection from Two Horizontally Aligned Circular Cylinders in Non-Newtonian Power-Law Fluids

TL;DR

This study numerically investigates how horizontal spacing affects natural convection from two aligned cylinders in non-Newtonian Power-law fluids, revealing optimal spacing for maximum heat transfer and developing a useful correlation for Nusselt number.

Contribution

It provides new insights into the influence of horizontal spacing and non-Newtonian fluid behavior on natural convection, including a developed correlation for Nusselt number.

Findings

Heat transfer increases with Gr and Prandtl number.

Shear-thinning fluids enhance convection, shear-thickening impede it.

Optimal spacing maximizes heat transfer before decreasing again.

Abstract

Laminar natural convection from two horizontally aligned isothermal cylinders in unconfined Power-law fluids has been investigated numerically. The effect of horizontal spacing (0<=(S/D)<=10) on both momentum and heat transfer characteristics has been delineated under the following pertinent parameters: Grashof number (10<=Gr<=1e3), Prandtl number (0.71<=n<=100), and Power-law index (0.4<=n<=1.6). The heat transfer characteristics are elucidated in terms of isotherms, local Nusselt number (Nu) distributions and average Nusselt number values, whereas the flow characteristics are interpreted in terms of streamlines, pressure contours, local distribution of the pressure drag and skin-friction drag coefficients along with the total drag coefficient values. The average Nusselt number shows a positive dependence on both Gr and Pr whereas it shows an adverse dependence on Power-law index (n). Overall, shear-thinning (n<1) fluid behavior promotes the convection whereas shear-thickening (n>1) behavior impedes it with reference to a Newtonian fluid (n=1). Furthermore, owing to the formation of a chimney effect, the heat transfer increases with decrease in horizontal spacing (S/D) and reaches a maximum value corresponding to the optimal spacing whereas the heat transfer drops significantly with further decrease in S/D. Finally, a correlation for Nu has been developed, which can be useful to academic researchers and practicing engineers.