Effects of Different Fin Spacings on the Nusselt Number and Reynolds Number in Perforated Finned Heat Exchangers

In this study, the effect of holes placed on perforated finned heat exchangers on convective heat transfer was experimentally investigated. Six-millimeter-diameter holes were opened on each circular fin on a heating tube in order to increase convective heat transfer. These holes were placed on the circular fins in such a way as to follow each other at the same chosen angle. The holes created turbulence in a region near the heating tube surface on the bottom of the fin. Experiments were then performed to analyze the effect of this turbulence on heat transfer and pressure drop. These experiments were carried out at five different fin spacings at the angular locations of 30° and 60° in order to determine the optimum fin spacing. Moreover, further experiments were carried out for counterflow and parallel-flow arrangements to determine the effects of the flow directions of the heating fluid and heated fluid. Results show an increase in Nusselt number with increasing modified Reynolds number. In addition, when different fin spacing to heating tube external diameter ratios were examined, at a ratio of 0.414 and angular locations of 30° and 60°, 11% and 8.6% increase in heat transfer were obtained, respectively, for parallel-flow arrangement compared to counterflow. For parallel flow, pressure drop values were 3.5% and 3.8% lower at 30° and 60°, respectively.