Nano-Fluid: Twisted Tape Inserts and Vortex Generators in Heat Exchanger

This project investigates heat transfer enhancement in a tubular heat exchanger using Computational Fluid Dynamics, with nanofluid flow as the central modelling theme. The working medium in the inner tube is a hot alumina (Al₂O₃) nanofluid — a base liquid carrying suspended nanoparticles that raise its effective thermal conductivity and alter its flow and heat-transfer behaviour relative to a conventional fluid. Treating this medium correctly is the core of the study, and it is combined with two passive enhancement devices, twisted-tape inserts and vortex generators, to examine how geometry and nanofluid properties together govern thermal performance.

Enhancing heat transfer in tubular exchangers is important across many industrial processes, where higher thermal efficiency translates directly into energy and cost savings. The configuration studied here has two sections: an inner passage carrying the hot alumina nanofluid and an outer passage carrying ambient air. As the nanofluid flows through the inner tube while the cooler air passes through the outer section, heat is transferred from the nanofluid to the air, and the simulation captures this cooling process and its effect on overall efficiency. The specific aim is to assess how the twisted-tape inserts and vortex generators reshape the flow patterns, heat-transfer characteristics and pressure drop within the tube.

The geometry was created in ANSYS Design Modeler and meshed in ANSYS Meshing with 4,427,809 elements. The simulation uses a pressure-based solver, appropriate for the incompressible flow typical of heat-exchanger applications, with a steady-state approach representing continuous operation under constant flow conditions. The RNG k-ε turbulence model is applied to capture the complex swirling and recirculating flow created by the inserts, and the energy equation is enabled to resolve the temperature field and heat transfer throughout the system.

The results give a detailed picture of the coupled flow and thermal behaviour. The pressure field shows high pressure near the vortex generators and low pressure in the core flow, with values ranging from about −544.64 Pa to 1960.45 Pa; the area-weighted average static pressure is 1953.92 Pa at the gas inlet and 206.98 Pa at the nanofluid inlet, with both outlets at atmospheric pressure. The temperature field clearly shows the cooling of the nanofluid as it traverses the tube, falling from 353.15 K at the inlet to 352.50 K at the outlet, while the air rises from 298.15 K to 323.31 K as it absorbs the transferred heat.

The velocity pathlines and contours reveal the complex flow induced by the geometry: the flow accelerates through the twisted-tape and vortex-generator regions, reaching velocities up to 0.5 m/s, and the twisted tape imposes a swirling motion that intensifies mixing and heat transfer. The turbulent kinetic energy peaks near the vortex generators and in their wakes, reaching up to 72.69 m²/s², and this elevated turbulence is what drives the enhanced mixing in those regions. The velocity vectors confirm zones of high velocity near the generators and in the core, clarifying the mechanisms responsible for the improved heat transfer.

Taken together, the results demonstrate the strong interplay between fluid flow and heat transfer in this configuration: the inserts and vortex generators create regions of high velocity and turbulence that directly enhance the cooling of the nanofluid. As a study in nanofluid flow modelling, the project shows how a nanofluid working medium, combined with passive turbulence-promoting geometry, can be represented in CFD to evaluate and optimise the thermal performance of tubular heat exchangers.