Heat-exchanger performance: Effect of orientation

For an extended-surface natural-convective type heat-exchanger in air, with its base at up to 40°C above the temperature of the ambient environment, the steady-state heat-transfer performances of the three most commonly employed orientations of the rectangular fins and base (namely vertical fins perpendicular to a vertical base, or protruding vertically upwards from a horizontal base, or horizontal fins attached to a vertical base) have been considered. The latter configuration is of no practical interest for the intended purpose because of its relatively inferior heat-transfer capabilities. If an optimal inter-fin separation of approximately 10 mm is adopted, all other conditions remaining invariant, a higher heat-transfer rate per unit base area is usually achieved from the array of fins when they are attached orthogonally to the vertical, rather than the horizontal, base; but this is not unequivocally so! More than 300 sets of experimental data, obtained from several different arrays of vertical rectangular highly polished duralumin fins protruding orthogonally either from a vertical, or upwards from a horizontal, rectangular highly polished duralumin base were assessed. The non-dimensional data correlations that emerged enable the average coefficient for heat-transfer from a finned surface to the ambient environment, for all the finned surfaces in these two types of configuration, to be easily predicted.