Steady-state free-convective cooling of heat exchangers with vertical rectangular fins: Effect of fin material

The steady-state rates of heat dissipation from an array of stainless-steel, vertical rectangular fins, under natural-convection conditions, have been measured experimentally when their base (which was either vertical or horizontal) was maintained at a uniform temperature of 20 or 40 K above that of the ambient environment. The fins were 3 mm thick and 500 mm long, and protruded 60 mm perpendicularly from the 500 mm x 190 mm rectangular base. For the vertically-based finned system, the optimal fin-separation Sopt corresponding to the maximum rate of heat loss to the ambient air was 12 ± 1 mm and remained almost invariant with respect to changes of the temperature excess [theta] above that of the ambient environment, for [theta] <= 40 K. However, for the orientation with vertical fins protruding upwards from the horizontal base, in this temperature range, Sopt increased from 20 ± 1 mm to 23 ± 1 mm when [theta] was reduced from 40 to 20 K. The present data have been compared with those previously obtained with similar configurations and orientations of duralumin fin arrays. Only relatively small reductions (~ 13·5 ± 3·5%) in the maximum rates of heat loss ensued, for the same value of [theta], when the heat exchanger was made of stainless steel rather than of duralumin, i.e. corresponding to a reduction of the material's thermal conductivity of more than 91%.