Enhancement of heat transfer and hydrodynamic performance in a double tube heat exchanger using transverse and helical turbulators with nanofluid

Double tube heat exchangers (DTHEs) are widely used in industrial thermal systems, where improving heat transfer efficiency
is critical for energy savings. This numerical study investigates the thermal–hydraulic performance of transverse and helical turbulator inserts with different rib geometries (rectangular, triangular, oval, and trapezoidal) used in combination with
a water-based SiO2 nanofluid in a counterflow DTHE. Steady-state laminar simulations were performed in ANSYS Fluent
for Reynolds numbers between 400 and 2000. The results show that helical turbulators significantly outperform transverse
designs, with the triangular helical turbulator achieving up to a 565% increase in the Nusselt number compared to pure water
without inserts, while transverse trapezoidal turbulators reached a maximum enhancement of 470%. Owing to enhanced swirl
generation and boundary-layer disruption, helical turbulators also yielded superior thermal–hydraulic performance, achieving
a maximum performance evaluation criterion (PEC) of 3.17, compared to 1.9 for transverse configurations. These findings
demonstrate the effectiveness of helical turbulator designs combined with nanofluids for improving DTHE performance in
laminar-flow industrial applications.