Turbulent Flow and Heat Transfer of Al₂O₃–CuO Hybrid Nanofluids in Helically Micro-Finned Tubes Using Mass-Based and Discrete-Phase Models

This numerical study investigates forced convective heat transfer and pressure drop in turbulent hybrid nanofluid flow through a helically finned tube with constant wall temperature. Both single-phase mass-based model (MBM) and discrete-phase method (DPM) approaches are employed to analyze and compare heat transfer characteristics in a three-dimensional helically micro-finned geometry. This study evaluated the effects of various volume flow rates between 0.4 to 1.2 m 3 /h (Reynolds numbers between 11510 to 34530) and nanoparticle concentrations ranging from 0.5% to 3% on water-base Al 2 O 3 –CuO hybrid nanofluids’ thermal and flow characteristics obtained from studied approaches. Results demonstrate that the utilized single-phase MBM predicts higher values for both average heat transfer coefficient and pressure drop compared to values obtained from the discrete phase method (DPM). For a 3.0% hybrid nanofluid, with volumetric flow rates ranging from 0.4 to 1.2 m 3 /h, the mean absolute percentage deviation (MAPD) in the average heat transfer coefficient between the multiphase DPM and single-phase MBM approaches, relative to pure water, is 1.5% to 7.5%. Also, by increasing the hybrid nanoparticle concentration from 0 to 3%, the deviation between single-phase and multi-phase approaches increases, reaching a maximum of 5.7% for the average heat transfer coefficient at a volume flow rate of 0.8 m 3 /h. However, at lower nanoparticle concentrations, both single-phase and multi-phase models produce similar results with minimal differences. The main novelty of the present work is that it compares the single-phase mass-based model with multi-phase DPM approaches. In addition, the combination of these modeling methods with the specific geometry of the present problem, turbulent regime, and the present hybrid nanofluid, for the first time in this study is considered. As a result, the single-phase approach offers a simpler and more cost-effective alternative to the more complex multi-phase methods for predicting nanofluid behavior in dilute solutions.