Thermohydraulic assessment of a spiral-finned triple concentric tube heat exchanger using water-based Al₂O₃, CuO and TiO₂ nanofluids

Abstract

The purpose of this work is to quantitatively examine the thermohydraulic performance of a spiral-finned triple concentric tube heat exchanger using various nanofluids. Using ANSYS Fluent 2020 R1, a 3D model is constructed, and a single-phase nanofluid approach is employed to solve the steady, pressure-based RNG k–ε equations. The limited research on nanofluids and fin design in triple concentric heat exchangers leads to poor heat transfer optimization. This can be improved using CFD-based analysis to optimize nanofluid properties and fin configurations. The present study has been validated with the numerical work of Amanuel and Mishra et al. with an average deviation of 1%, while 9.39% for experimental work of Singh et al. due to differences in geometry, operating parameters, and boundary conditions between the studies. This is offered in good agreement taking into account to highlight the consistency of the numerical trends as well as the experimental study. However, the parallel flow scenarios with Reynolds numbers (Re) ranging from 2500 to 10000 are performed with an insulated outer wall at inlet temperatures of 333 K for the hot annulus, 303 K for the inner tube, and 313 K for the outer annulus, utilizing water and nanofluids of Al₂O₃, CuO, and TiO₂ at 0–3% volume. In comparison to the plain triple tube, the results indicate that the spiral fin increases the Nusselt number (Nu) by approximately 30–40%. Nanofluids also increase Nu, most notably at lower Re, with diminishing gains above 2%. As anticipated, the pressure drop increased with the Reynolds number and nanoparticle concentration, while the friction factor decreased with the Reynolds number but increased marginally with nanoparticle loading. A comparatively higher thermal performance factor (TPF) has been observed at low Reynolds numbers, which indicates that they effectively improve heat transfer at slower flow rates. Moreover, the nanoparticles generally aid in improving heat transfer, as seen by the fact that the nanofluids with the concentrations of 2% Al 2 O 3 and 2% TiO₂ tend to maintain better thermal performance than others. With a moderate pumping penalty and strong heat-transfer enhancement, the spiral fin geometry with 1–2% nanofluid offers the best overall performance–cost trade-of. The scope of triple concentric tubes heat exchangers improves thermal efficiency in low-energy systems; however, the heat transfer capabilities of these systems can be further enhanced by modifying geometries and utilizing nanofluids.