Natural Convection Correlations of Circular Finned Tube Heat Exchanger

An experimental study has been conducted on natural convection heat transfer for seventeen kinds of circular finned tube heat exchanger. The transient method was used to obtain the heat transfer coefficient. The experimental data were presented and their characteristics lengths were discussed. The experimental data were presented and correlated in the ranges of 27 < Ra_Dh < 2300, 1.2 < D_o/D_i < 2.8, and 0.12 < P_f/D_i < 0.26. The Nusselt number correlated with the quarter power of the Rayleigh number, based on the hydraulic diameter, for the small diameter fins, the same as laminar natural convection; however, the correlation was with the half power for the large fin diameters and small fin pitches.