Analysis of the effects of perforated annular fins on thermal-hydraulic performance and vortex generation in a double-pipe heat exchanger

Perforated structures are commonly incorporated into fins to enhance the thermal–hydraulic performance of heat exchangers. However, the influence of total porosity in perforated fins has often been overlooked in previous studies. Hence, this study conducts a systematic parametric analysis of the design of perforated annular fins, adopting a three-fold strategy: Design 1 varies the porosity by changing the hole number, Design 2 by changing the hole diameter, and Design 3 examines the combined influence of hole number and diameter while maintaining a fixed porosity. To obtain a high-fidelity numerical simulation of such complex turbulent flows, the SST k-? turbulence model was adopted. Moreover, the numerical model is validated against empirical correlations and available experimental data. The results demonstrated that the introduction of perforations reduces the recirculation zone and transverse vortices behind the fins, while simultaneously disrupting the low velocity region upstream of the annular fins and generating additional local flow disturbances and longitudinal vortices. Both the average Nusselt number (Nu¯[jls-end-space/]) and pressure drop (?p[jls-end-space/]) decrease with the increase of porosity. However, when porosity is fixed, the increase in heat transfer enhancement and pressure drop caused by changes in the number and size of holes is limited, which means that porosity is the key factor dominating performance in this design. Furthermore, under the present fin geometry parameters, Reynolds number (Re) range, and thermal boundary conditions, a porosity of 0.2 provides the highest PEC value in this study, reaching 1.186 at Re = 4540. © 2026 Published by Elsevier Ltd.