Numerical analysis of thermo-hydraulic performance in double-twisted tube heat exchangers using Al ₂ O ₃ nanofluid: part 1 effect of configurations tube

This computational study investigates the thermo-hydraulic performance of five distinct double-tube heat exchanger configurations with twisted geometries: Double Circular Twisted Tube (DCTTHE), Double Elliptical Twisted Tube (DETTHE), Double Triangle Twisted Tube (DTTTHE), and Double Twisted Square Tube (DTSTHE). To improve heat transfer efficiency in compact systems without excessively increasing hydraulic losses. It is hypothesized that simultaneous twisting of both inner and outer tubes can intensify secondary flow structures, thereby significantly enhancing thermal performance compared to other geometrical configurations. A three-dimensional finite volume model, employing the standard k - ε turbulence model and validated against established literature, was used to simulate turbulent flow (Reynolds number range: 5,000–30,000) with Al 2 O 3 -water nanofluid at a 4 % volume concentration and a constant twist ratio of 5. The analysis focused on key performance metrics, including heat transfer rate, effectiveness, Nusselt number, and pressure drop. Results demonstrate that the DTSTHE configuration, characterized by the concurrent twisting of both inner and outer tubes, generated the most intense secondary flow and vortex structures. This led to superior thermal performance, achieving the highest heat exchanger effectiveness and overall performance factor across the studied Reynolds number range. However, this thermal enhancement was universally accompanied by an increased pressure drop, with the DTTTHE geometry exhibiting the most significant hydraulic penalty. The study concludes that the DTSTHE providing substantial heat transfer augmentation while maintaining a manageable pressure drop compared to other twisted geometries.