Natural Convection Around Three Horizontal Cylinders in Vertical Array: A Numerical Approach

The present numerical study explores the flow physics and heat transfer characteristics around three unconfined inline horizontally placed cylinders arranged in a vertical array subjected to ambient air. It investigates the effect of Rayleigh number (i.e., 10² ≤ Ra ≤ 10⁶) and the center-to-center spacing (1≤ S/D ≤ 9). The study shows that the augmentation or reduction of heat transfer rate from an individual cylinder in the array to that of a single unconfined cylinder under identical conditions strongly depends on the separation distance and Rayleigh number. Moreover, the average Nu from the bottom cylinder deteriorates only at very close spacing, whereas after S/D ≥ 3, it attains an asymptotic value to that of a single cylinder. The heat transfer rates from the middle and top cylinders relative to a single cylinder also deteriorate drastically at close spacing. In contrast, a slight enhancement is observed at relatively large spacing and higher Ra.