Development of improved heat transfer of double helical pipe heat exchangers using nano-fluids and perforated curved tabulators

This study examines a helical double-pipe heat exchanger's thermal and fluid flow performance incorporating a curved perforated turbulator and hybrid nanofluids. Two nanofluids, Al 2 O 3 -TiO 2 /water, and Ag-HEG/water, were compared with pure water and a baseline case without a turbulator to evaluate heat transfer enhancement. The research is divided into two phases. In the first phase, the thermal and hydrothermal behavior of two hybrid nanofluids—Al 2 O 3 -TiO 2 /water and Ag-HEG/water—was evaluated and compared to pure water and a baseline case without turbulators to assess their effectiveness. In the second phase, the influence of nanoparticle volume concentration (φ 1 = φ 2 ) of the selected hybrid nanofluid according to the results obtained from the first section, Al 2 O 3 -TiO 2 /water, was analyzed over a range of 0.1–0.5. The curved turbulator, featuring inner ribs and perforations, was designed to induce swirl flows, enhance fluid mixing, and disrupt thermal boundary layers to improve heat transfer. The numerical analysis was performed using the finite volume method in a commercial code. The findings of the first section show that Al 2 O 3 -TiO 2 /water achieves the highest heat transfer rate; its heat transfer coefficient is about 1.04 %, 2.63 %, and 18.19 % greater than cases with Ag-HEG/water, pure water, and without turbulator, respectively at Re = 14,000. However, the thermal performance factor of the case without a turbulator is more significant than that of all models because of the high pressure drop in all cases, including the proposed turbulator. In the second phase, the outcomes illustrate that by raising the volume concentration of Al 2 O 3 -TiO 2 /water hybrid nanofluid from 0.1 to 0.3 (200 % growth) and 0.5 (400 % growth), the heat transfer coefficient augments by about 1.56 % and 3.65 %, respectively. Concerning the thermal performance factor, although increasing the volume concentration does not help to improve it compared to the case without a turbulator, expanding the volume concentration from 0.1 to 0.3 leads to an increase in the thermal performance factor by about 5.85 % at Re = 10,000.