Numerical and experimental study of natural convection heat transfer characteristics for vertical annular finned tube heat exchanger

This study uses three-dimensional computational fluid dynamics (CFD) commercial package along with the inverse method and experimental data to investigate the natural convection heat transfer and fluid flow characteristics of the single-tube vertical annular finned tube heat exchanger for various values of fin spacing and tube diameter. The air temperature and velocity distributions, the fin surface temperature and the heat transfer coefficient on the fins are determined by the FLUENT along with various flow models in the box with the upward opening. The inverse method along with the finite difference method and the experimental temperature data is applied to determine the fin temperature and heat transfer coefficient for the smaller tube. More accurate results are obtained by the appropriate flow model, if the heat transfer coefficient obtained is close to the inverse results and matches existing correlations. The fin temperature obtained at the selected measurement locations coincides with the experimental data. The results show that the zero-equation turbulence model is more suitable for this problem than laminar and RNG k-ε turbulence models. The grid independence assumption cannot be appropriate. The proposed correlations between the Nusselt number and the Rayleigh number are close to FLUENT and inverse results.