Effect of novel turbulators on the hydrothermal performance of counterflow double tube heat exchanger using nanofluids

•Novel turbulator designs in DTHEs yield unprecedented enhancements in heat transfer rate.•Turbulator shapes analyzed with nanofluids CuO, SiO2, Al2O3 water-based nanofluids in a single-phase model; trapezoidal ribs outperform others in Nusselt number and friction factor.•Oval ribs in DTHEs demonstrate superior performance evaluation criteria across studied shapes.•Rib height was identified as the most influential geometrical parameter on heat transfer improvement. Double pipe heat exchangers are widely used across various industries. Enhancing their performance not only benefits these industries but also contributes to reduced fossil fuel consumption and pollution. This study employs the passive method with a combination turbulator insertion and nanofluid technique to enhance the heat transfer rate and improve the double tube heat exchanger performance. The novelty of this study lies in the use of new turbulator insertions and various nanofluids to investigate the heat transfer and fluid flow characteristics under laminar and counter flow configuration. The study examined four types of turbulator insertions, including triangular, rectangular, trapezoidal, and oval, in conjunction with CuO, SiO2, Al2O3 water-based nanofluids in a single-phase model. The findings revealed that the trapezoidal ribs exhibited higher Nusselt number and friction factor than the other rib shapes. Conversely, the oval ribs demonstrated a better performance evaluation criteria than the other rib shapes. Furthermore, the study explored different geometrical parameters such as rib width, height, and spacing, determining that rib height has the most significant impact on enhancing the heat transfer. The study achieved maximum performance evaluation criteria of 1.2 and 1.9 for SiO2 nanofluid without turbulator insertion and with turbulator insertion, respectively.