Numerical Analysis on Natural Convection Heat Transfer in a Single Circular Fin-Tube Heat Exchanger (Part 2): Correlations for Limiting Cases

This research focused on the correlations associated with the physics of natural convection in circular fin-tube models. The limiting conditions are defined by two conditions. The lower limit ([Formula: see text] → 1, s/D = finite value) corresponds to a horizontal circular tube, while the upper limit ([Formula: see text] → ∞, s/D << 1) corresponds to vertical flat plates. In this paper, we proposed a corrected correlation based on empirical result. The circular fin-tube heat exchanger was divided into the A and B types, the categorizing criteria being [Formula: see text] , where [Formula: see text] and [Formula: see text] refer to the diameter of the circular tube and the diameter of the circular fin, respectively. Moreover, with the computational fluid dynamics technique used to investigate the limiting conditions, the parametric range was extended substantially in this research for type B, namely 1.2 < [Formula: see text] ≤ 10. The complex correlation was also simplified to the form [Formula: see text] = [Formula: see text] , where [Formula: see text] and [Formula: see text] are the functions of the diameter ratio [Formula: see text].