Optimal configuration of helically finned tubes for enhanced thermal performance of Al2O3–CuO/water multi-phase hybrid nanofluids in turbulent flow: a discrete phase method approach

Purpose This study aims to investigate the flow and heat transfer characteristics of tubes equipped with helical micro-fins in various configurations to improve their hydrodynamic and thermal performance. Design/methodology/approach Seven cases were studied: a tube without fins (Case 1) and tubes with nine helical micro-fins in different configurations (Cases 2–7). Their thermal and hydrodynamic behavior was evaluated at Reynolds numbers from 11,510 to 34,530. To investigate the effects of helical micro-fins on thermal performance and turbulent flow in tubes, a multi-phase hybrid nanofluid, composed of Al2O3 and CuO nanoparticles in water was chosen as the working fluid. The discrete phase model (DPM) was used to simulate flow and heat transfer for various micro-fin configurations. The performance evaluation criteria (PEC) was used to assess the optimal micro-finned tube design by balancing heat transfer enhancement and pressure drop increase. Findings Depending on the fin configurations, implementing helical micro-fins in tubes can enhance or diminish hydrodynamic and thermal performance compared to finless tubes. The spacing between individual fins in each fin group (α) and the spacing between adjacent fin groups (β) significantly affect both the heat transfer coefficient and the pressure drop. Increasing the distance between fin groups while decreasing the distance between fins within groups boosts the convective heat transfer coefficient on average by 10.1% in Case 6 and 11.4% in Case 7, compared to the uniform fin distribution in Case 4. Moreover, this research demonstrated that selecting an optimal helical fin configuration can enhance the PEC of the best configuration (Case 7) by up to 9.0% compared to uniform helical micro-fins and 4.6% compared to finless tubes. Originality/value To the best of the authors’ knowledge, this work is original in that, for the first time, it systematically investigates the combined effects of varying both intra-group (α) and inter-group (β) spacing of helical micro-fins on the thermal and hydrodynamic performance of tubes using a multi-phase hybrid nanofluid. Unlike previous studies that considered uniform fin distributions or single nanofluid phases, this study uniquely uses Al2O3–CuO/water as the working fluid and uses the DPM to simulate particle dynamics and heat transfer.