Geometry effects on turbulent flow and heat transfer in internally finned tubes

A parametric study has been performed on turbulent flow and heat transfer i n internally finned tubes. For a rectangular fin profile, the effects of fi n number N, fin width s, fin height H, and helix angle gamma were numerical ly investigated for the conditions of N = 10 similar to 40, H =0.03 similar to 0.1, s = 0.05 similar to 0.22, gamma =10 deg similar to 40 deg, and Re = 40,000. In addition, the performance of three fin profiles-rectangle, tri angle, and round crest-with the same fin heights, width, and helix angles w ere compared for Reynolds numbers between 10,000 and 70,000. Rectangular an d triangular fins behave similarly; for some geometric conditions the round crest fin has lower friction factors and Nusselt numbers (17 and 10 percen t, respectively) than the rectangular fin. However, when the number of fins is large, the round crest fin can have larger friction factors (about 16 p ercent). Damping of turbulence energy in the interfin region is credited fo r the reversal of the typical trends.