Flow and heat transfer performances of directly printed curved-rectangular vortex generators in a compact fin-tube heat exchanger

Abstract

In this study, the flow and heat transfer characteristics of newly configured curved-rectangular vortex generators (VGs) in a compact fin-tube heat exchanger were numerically investigated. The proposed VGs were designed to be directly printed rather than being punched out from the plate fin surfaces. The influences of VGs on the overall flow structure and thermal mixing, and near-wall flow and thermal features were characterised in detail. The mechanisms of heat transfer enhancement were explored in terms of the secondary flow and field synergy theories. Results indicate two main mechanisms for the suppression of recirculation flows by applying VGs. The lowered local synergy angle rather than the enhanced local secondary flow intensity is the immediate mechanism for the enhanced heat transfer performance. Parametric analysis indicates that increasing VG height and radius increases both Nusselt number (Nu) and friction factor (f). An optimal VG configuration for the thermo-hydraulic performance is identified at the VG height ratio of 0.8 and radius ratio of 1.55, by which the obtained performance evaluation criterion (PEC) is about 1.3–1.5 times as that of the baseline over the tested Re range. Correlations are further developed to predict the Nu, f and PEC for future preliminary design purposes.