CONJUGATE HEAT-TRANSFER OF A FINNED TUBE .A. HEAT-TRANSFER BEHAVIOR AND OCCURRENCE OF HEAT-TRANSFER REVERSAL

The conjugate heat transfer in a high-performance finned-tube heat exchanger element was calculated for three-dimensional thermally and hydrodynamically developing laminar flows. The influence of Reynolds number Re and a fin efficiency parameter Fi (ratio of fin to fluid conductivity times fin thickness to fin pitch) on the heat transfer behavior has been studied. Flow patterns, pressure distribution, Nusselt number distribution, heat flux distribution, and fin efficiency are presented. The part of the fin upstream of the tube is much more efficient than the downstream part. A unique heat transfer phenomenon, a directional reversal of the heat transfer, occurred locally on the fin in the tube wake for small Fi and large Re. This can be interpreted as three-dimensional interaction of convection and the fin conduction in the tube wake, when the flow is dominated by a strong horseshoe vortex and a dead water zone with recirculation.