  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.
