Heat Transfer Enhancement Analysis of a Rotating Twisted Tape Heat Exchanger Using an Al₂O₃/Graphene/Water Hybrid Nanofluid

Heat exchangers are widely used in thermal systems in the chemical, energy, and nuclear engineering sectors. To improve their thermal performance, this study investigates an effective heat transfer enhancement strategy based on the synergistic coupling of a rotating twisted tape and hybrid nanofluids. An experimental platform featuring a double-pipe heat exchanger equipped with a rotating twisted tape was developed, and a hybrid nanofluid composed of flake-shaped graphene and spherical alumina (Al₂O₃) nanoparticles was prepared. The influence of different nanoparticle compositions on the heat transfer and flow characteristics of the heat exchanger was systematically examined. The results indicate that hybrid nanofluids substantially enhance the thermal performance of the rotating twisted tape heat exchanger. As the Reynolds number increases from ۲۰,۰۰۰ to ۱۸۰,۰۰۰, the overall heat transfer coefficient obtained using the hybrid nanofluid containing ۱۲۰۰ g Al₂O₃ and ۶۰۰ g graphene increases by ۴۱.۱% to ۴۷.۵% compared pure water. In contrast, the enhancement ratios of the Nusselt number, friction factor, and Stanton number decrease from ۵۱.۶%, ۹۳.۷%, and ۸۲.۷% down to ۱۰.۰%, ۲۵.۶%, and ۳۴.۸%, respectively. This trend indicates a diminishing contribution from nanoparticle-induced conductive networks and micro-perturbation effects at higher Reynolds numbers. A Performance Evaluation Criterion (PEC) analysis shows that within the Reynolds number range around ۴۰,۰۰۰, the hybrid nanofluid achieves a ۲۱.۷% improvement in overall performance compared to water. This advantage gradually diminishes as the Reynolds number increases. An economic assessment based on the performance-to-price factor further reveals that within the favorable performance regime, lower-concentration formulations consisting of ۶۰۰ g of graphene combined with either ۶۰ g or ۱۲۰ g of Al₂O₃ provide the optimal balance between heat transfer enhancement and material cost among the tested formulations.

کلیدواژه ها:

Spinning ribbon heat exchanger ، Hybrid nanofluid ، Graphene nanoplatelets ، Al₂O₃ Nanoparticles ، Heat transfer fluid