Numerical modeling of finned heat exchangers

Abstract

A numerical investigation of annular finned tubes was performed using the computational fluid dynamics (CFD) software ANSYS FLUENT. The effects of fin spacing, fin height, fin thickness, and fin material on the overall heat transfer and pressure drop were determined for a single row of finned tubes in crossflow.As fin height (hf) increased, the predicted overall heat transfer increased. The magnitude of the increase in overall heat transfer was larger for smaller fin spacing (s). A similar trend was seen with the pressure drop – as the fin height increased the pressure drop increased with the magnitude of the increase being more significant for smaller fin spacings. For a fin spacing over tube diameter ratio of greater than one-third, the increase in pressure drop with fin height is very small.The effect of the fin thickness on heat transfer and pressure drop was much less significant than the fin spacing and fin height. Increasing the fin thickness showed minor increases in heat transfer and modest increases in pressure drop. While heat transfer also increased as the thermal conductivity of the material increased, the results showed relatively small differences in the heat transfer for plain carbon steel, aluminum, and copper. This is because the thermal resistance from convection became much larger than the thermal resistance from conduction in the fin.For s/hf > 1.5 the pressure drop remains relatively constant. On the other hand, the heat transfer shows a significant decrease as the ratio of s/hf goes from 1.5 to 6. This suggests that for the range of parameters used in the simulations, there is no value to designing a finned tube with s/hf > 1.5.